// SPDX-License-Identifier: GPL-2.0
/*
 * Shared application/kernel submission and completion ring pairs, for
 * supporting fast/efficient IO.
 *
 * A note on the read/write ordering memory barriers that are matched between
 * the application and kernel side.
 *
 * After the application reads the CQ ring tail, it must use an
 * appropriate smp_rmb() to pair with the smp_wmb() the kernel uses
 * before writing the tail (using smp_load_acquire to read the tail will
 * do). It also needs a smp_mb() before updating CQ head (ordering the
 * entry load(s) with the head store), pairing with an implicit barrier
 * through a control-dependency in io_get_cqe (smp_store_release to
 * store head will do). Failure to do so could lead to reading invalid
 * CQ entries.
 *
 * Likewise, the application must use an appropriate smp_wmb() before
 * writing the SQ tail (ordering SQ entry stores with the tail store),
 * which pairs with smp_load_acquire in io_get_sqring (smp_store_release
 * to store the tail will do). And it needs a barrier ordering the SQ
 * head load before writing new SQ entries (smp_load_acquire to read
 * head will do).
 *
 * When using the SQ poll thread (IORING_SETUP_SQPOLL), the application
 * needs to check the SQ flags for IORING_SQ_NEED_WAKEUP *after*
 * updating the SQ tail; a full memory barrier smp_mb() is needed
 * between.
 *
 * Also see the examples in the liburing library:
 *
 *      git://git.kernel.dk/liburing
 *
 * io_uring also uses READ/WRITE_ONCE() for _any_ store or load that happens
 * from data shared between the kernel and application. This is done both
 * for ordering purposes, but also to ensure that once a value is loaded from
 * data that the application could potentially modify, it remains stable.
 *
 * Copyright (C) 2018-2019 Jens Axboe
 * Copyright (c) 2018-2019 Christoph Hellwig
 */
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/errno.h>
#include <linux/syscalls.h>
#include <linux/compat.h>
#include <net/compat.h>
#include <linux/refcount.h>
#include <linux/uio.h>
#include <linux/bits.h>

#include <linux/sched/signal.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/percpu.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/bvec.h>
#include <linux/net.h>
#include <net/sock.h>
#include <net/af_unix.h>
#include <net/scm.h>
#include <linux/anon_inodes.h>
#include <linux/sched/mm.h>
#include <linux/uaccess.h>
#include <linux/nospec.h>
#include <linux/sizes.h>
#include <linux/hugetlb.h>
#include <linux/highmem.h>
#include <linux/namei.h>
#include <linux/fsnotify.h>
#include <linux/fadvise.h>
#include <linux/eventpoll.h>
#include <linux/splice.h>
#include <linux/task_work.h>
#include <linux/pagemap.h>
#include <linux/io_uring.h>
#include <linux/tracehook.h>

#define CREATE_TRACE_POINTS
#include <trace/events/io_uring.h>

#include <uapi/linux/io_uring.h>

#include "internal.h"
#include "io-wq.h"

#define IORING_MAX_ENTRIES      32768
#define IORING_MAX_CQ_ENTRIES   (2 * IORING_MAX_ENTRIES)
#define IORING_SQPOLL_CAP_ENTRIES_VALUE 8

/*
 * Shift of 9 is 512 entries, or exactly one page on 64-bit archs
 */
#define IORING_FILE_TABLE_SHIFT 9
#define IORING_MAX_FILES_TABLE  (1U << IORING_FILE_TABLE_SHIFT)
#define IORING_FILE_TABLE_MASK  (IORING_MAX_FILES_TABLE - 1)
#define IORING_MAX_FIXED_FILES  (64 * IORING_MAX_FILES_TABLE)
#define IORING_MAX_RESTRICTIONS (IORING_RESTRICTION_LAST + \
                                 IORING_REGISTER_LAST + IORING_OP_LAST)

#define IO_RSRC_TAG_TABLE_SHIFT 9
#define IO_RSRC_TAG_TABLE_MAX   (1U << IO_RSRC_TAG_TABLE_SHIFT)
#define IO_RSRC_TAG_TABLE_MASK  (IO_RSRC_TAG_TABLE_MAX - 1)

#define IORING_MAX_REG_BUFFERS  (1U << 14)

#define SQE_VALID_FLAGS (IOSQE_FIXED_FILE|IOSQE_IO_DRAIN|IOSQE_IO_LINK| \
                                IOSQE_IO_HARDLINK | IOSQE_ASYNC | \
                                IOSQE_BUFFER_SELECT)
#define IO_REQ_CLEAN_FLAGS (REQ_F_BUFFER_SELECTED | REQ_F_NEED_CLEANUP | \
                                REQ_F_POLLED | REQ_F_INFLIGHT | REQ_F_CREDS)

#define IO_TCTX_REFS_CACHE_NR   (1U << 10)

struct io_uring {
        u32 head ____cacheline_aligned_in_smp;
        u32 tail ____cacheline_aligned_in_smp;
};

/*
 * This data is shared with the application through the mmap at offsets
 * IORING_OFF_SQ_RING and IORING_OFF_CQ_RING.
 *
 * The offsets to the member fields are published through struct
 * io_sqring_offsets when calling io_uring_setup.
 */
struct io_rings {
        /*
         * Head and tail offsets into the ring; the offsets need to be
         * masked to get valid indices.
         *
         * The kernel controls head of the sq ring and the tail of the cq ring,
         * and the application controls tail of the sq ring and the head of the
         * cq ring.
         */
        struct io_uring         sq, cq;
        /*
         * Bitmasks to apply to head and tail offsets (constant, equals
         * ring_entries - 1)
         */
        u32                     sq_ring_mask, cq_ring_mask;
        /* Ring sizes (constant, power of 2) */
        u32                     sq_ring_entries, cq_ring_entries;
        /*
         * Number of invalid entries dropped by the kernel due to
         * invalid index stored in array
         *
         * Written by the kernel, shouldn't be modified by the
         * application (i.e. get number of "new events" by comparing to
         * cached value).
         *
         * After a new SQ head value was read by the application this
         * counter includes all submissions that were dropped reaching
         * the new SQ head (and possibly more).
         */
        u32                     sq_dropped;
        /*
         * Runtime SQ flags
         *
         * Written by the kernel, shouldn't be modified by the
         * application.
         *
         * The application needs a full memory barrier before checking
         * for IORING_SQ_NEED_WAKEUP after updating the sq tail.
         */
        u32                     sq_flags;
        /*
         * Runtime CQ flags
         *
         * Written by the application, shouldn't be modified by the
         * kernel.
         */
        u32                     cq_flags;
        /*
         * Number of completion events lost because the queue was full;
         * this should be avoided by the application by making sure
         * there are not more requests pending than there is space in
         * the completion queue.
         *
         * Written by the kernel, shouldn't be modified by the
         * application (i.e. get number of "new events" by comparing to
         * cached value).
         *
         * As completion events come in out of order this counter is not
         * ordered with any other data.
         */
        u32                     cq_overflow;
        /*
         * Ring buffer of completion events.
         *
         * The kernel writes completion events fresh every time they are
         * produced, so the application is allowed to modify pending
         * entries.
         */
        struct io_uring_cqe     cqes[] ____cacheline_aligned_in_smp;
};

enum io_uring_cmd_flags {
        IO_URING_F_NONBLOCK             = 1,
        IO_URING_F_COMPLETE_DEFER       = 2,
};

struct io_mapped_ubuf {
        u64             ubuf;
        u64             ubuf_end;
        unsigned int    nr_bvecs;
        unsigned long   acct_pages;
        struct bio_vec  bvec[];
};

struct io_ring_ctx;

struct io_overflow_cqe {
        struct io_uring_cqe cqe;
        struct list_head list;
};

struct io_fixed_file {
        /* file * with additional FFS_* flags */
        unsigned long file_ptr;
};

struct io_rsrc_put {
        struct list_head list;
        u64 tag;
        union {
                void *rsrc;
                struct file *file;
                struct io_mapped_ubuf *buf;
        };
};

struct io_file_table {
        /* two level table */
        struct io_fixed_file **files;
};

struct io_rsrc_node {
        struct percpu_ref               refs;
        struct list_head                node;
        struct list_head                rsrc_list;
        struct io_rsrc_data             *rsrc_data;
        struct llist_node               llist;
        bool                            done;
};

typedef void (rsrc_put_fn)(struct io_ring_ctx *ctx, struct io_rsrc_put *prsrc);

struct io_rsrc_data {
        struct io_ring_ctx              *ctx;

        u64                             **tags;
        unsigned int                    nr;
        rsrc_put_fn                     *do_put;
        atomic_t                        refs;
        struct completion               done;
        bool                            quiesce;
};

struct io_buffer {
        struct list_head list;
        __u64 addr;
        __u32 len;
        __u16 bid;
};

struct io_restriction {
        DECLARE_BITMAP(register_op, IORING_REGISTER_LAST);
        DECLARE_BITMAP(sqe_op, IORING_OP_LAST);
        u8 sqe_flags_allowed;
        u8 sqe_flags_required;
        bool registered;
};

enum {
        IO_SQ_THREAD_SHOULD_STOP = 0,
        IO_SQ_THREAD_SHOULD_PARK,
};

struct io_sq_data {
        refcount_t              refs;
        atomic_t                park_pending;
        struct mutex            lock;

        /* ctx's that are using this sqd */
        struct list_head        ctx_list;

        struct task_struct      *thread;
        struct wait_queue_head  wait;

        unsigned                sq_thread_idle;
        int                     sq_cpu;
        pid_t                   task_pid;
        pid_t                   task_tgid;

        unsigned long           state;
        struct completion       exited;
};

#define IO_IOPOLL_BATCH                 8
#define IO_COMPL_BATCH                  32
#define IO_REQ_CACHE_SIZE               32
#define IO_REQ_ALLOC_BATCH              8

struct io_comp_state {
        struct io_kiocb         *reqs[IO_COMPL_BATCH];
        unsigned int            nr;
        /* inline/task_work completion list, under ->uring_lock */
        struct list_head        free_list;
};

struct io_submit_link {
        struct io_kiocb         *head;
        struct io_kiocb         *last;
};

struct io_submit_state {
        struct blk_plug         plug;
        struct io_submit_link   link;

        /*
         * io_kiocb alloc cache
         */
        void                    *reqs[IO_REQ_CACHE_SIZE];
        unsigned int            free_reqs;

        bool                    plug_started;

        /*
         * Batch completion logic
         */
        struct io_comp_state    comp;

        /*
         * File reference cache
         */
        struct file             *file;
        unsigned int            fd;
        unsigned int            file_refs;
        unsigned int            ios_left;
};

struct io_ring_ctx {
        /* const or read-mostly hot data */
        struct {
                struct percpu_ref       refs;

                struct io_rings         *rings;
                unsigned int            flags;
                unsigned int            compat: 1;
                unsigned int            drain_next: 1;
                unsigned int            eventfd_async: 1;
                unsigned int            restricted: 1;
                unsigned int            off_timeout_used: 1;
                unsigned int            drain_active: 1;
        } ____cacheline_aligned_in_smp;

        /* submission data */
        struct {
                struct mutex            uring_lock;

                /*
                 * Ring buffer of indices into array of io_uring_sqe, which is
                 * mmapped by the application using the IORING_OFF_SQES offset.
                 *
                 * This indirection could e.g. be used to assign fixed
                 * io_uring_sqe entries to operations and only submit them to
                 * the queue when needed.
                 *
                 * The kernel modifies neither the indices array nor the entries
                 * array.
                 */
                u32                     *sq_array;
                struct io_uring_sqe     *sq_sqes;
                unsigned                cached_sq_head;
                unsigned                sq_entries;
                struct list_head        defer_list;

                /*
                 * Fixed resources fast path, should be accessed only under
                 * uring_lock, and updated through io_uring_register(2)
                 */
                struct io_rsrc_node     *rsrc_node;
                struct io_file_table    file_table;
                unsigned                nr_user_files;
                unsigned                nr_user_bufs;
                struct io_mapped_ubuf   **user_bufs;

                struct io_submit_state  submit_state;
                struct list_head        timeout_list;
                struct list_head        cq_overflow_list;
                struct xarray           io_buffers;
                struct xarray           personalities;
                u32                     pers_next;
                unsigned                sq_thread_idle;
        } ____cacheline_aligned_in_smp;

        /* IRQ completion list, under ->completion_lock */
        struct list_head        locked_free_list;
        unsigned int            locked_free_nr;

        const struct cred       *sq_creds;      /* cred used for __io_sq_thread() */
        struct io_sq_data       *sq_data;       /* if using sq thread polling */

        struct wait_queue_head  sqo_sq_wait;
        struct list_head        sqd_list;

        unsigned long           check_cq_overflow;

        struct {
                unsigned                cached_cq_tail;
                unsigned                cq_entries;
                struct eventfd_ctx      *cq_ev_fd;
                struct wait_queue_head  poll_wait;
                struct wait_queue_head  cq_wait;
                unsigned                cq_extra;
                atomic_t                cq_timeouts;
                struct fasync_struct    *cq_fasync;
                unsigned                cq_last_tm_flush;
        } ____cacheline_aligned_in_smp;

        struct {
                spinlock_t              completion_lock;

                /*
                 * ->iopoll_list is protected by the ctx->uring_lock for
                 * io_uring instances that don't use IORING_SETUP_SQPOLL.
                 * For SQPOLL, only the single threaded io_sq_thread() will
                 * manipulate the list, hence no extra locking is needed there.
                 */
                struct list_head        iopoll_list;
                struct hlist_head       *cancel_hash;
                unsigned                cancel_hash_bits;
                bool                    poll_multi_queue;
        } ____cacheline_aligned_in_smp;

        struct io_restriction           restrictions;

        /* slow path rsrc auxilary data, used by update/register */
        struct {
                struct io_rsrc_node             *rsrc_backup_node;
                struct io_mapped_ubuf           *dummy_ubuf;
                struct io_rsrc_data             *file_data;
                struct io_rsrc_data             *buf_data;

                struct delayed_work             rsrc_put_work;
                struct llist_head               rsrc_put_llist;
                struct list_head                rsrc_ref_list;
                spinlock_t                      rsrc_ref_lock;
        };

        /* Keep this last, we don't need it for the fast path */
        struct {
                #if defined(CONFIG_UNIX)
                        struct socket           *ring_sock;
                #endif
                /* hashed buffered write serialization */
                struct io_wq_hash               *hash_map;

                /* Only used for accounting purposes */
                struct user_struct              *user;
                struct mm_struct                *mm_account;

                /* ctx exit and cancelation */
                struct llist_head               fallback_llist;
                struct delayed_work             fallback_work;
                struct work_struct              exit_work;
                struct list_head                tctx_list;
                struct completion               ref_comp;
        };
};

struct io_uring_task {
        /* submission side */
        int                     cached_refs;
        struct xarray           xa;
        struct wait_queue_head  wait;
        const struct io_ring_ctx *last;
        struct io_wq            *io_wq;
        struct percpu_counter   inflight;
        atomic_t                inflight_tracked;
        atomic_t                in_idle;

        spinlock_t              task_lock;
        struct io_wq_work_list  task_list;
        unsigned long           task_state;
        struct callback_head    task_work;
};

/*
 * First field must be the file pointer in all the
 * iocb unions! See also 'struct kiocb' in <linux/fs.h>
 */
struct io_poll_iocb {
        struct file                     *file;
        struct wait_queue_head          *head;
        __poll_t                        events;
        bool                            done;
        bool                            canceled;
        struct wait_queue_entry         wait;
};

struct io_poll_update {
        struct file                     *file;
        u64                             old_user_data;
        u64                             new_user_data;
        __poll_t                        events;
        bool                            update_events;
        bool                            update_user_data;
};

struct io_close {
        struct file                     *file;
        int                             fd;
};

struct io_timeout_data {
        struct io_kiocb                 *req;
        struct hrtimer                  timer;
        struct timespec64               ts;
        enum hrtimer_mode               mode;
};

struct io_accept {
        struct file                     *file;
        struct sockaddr __user          *addr;
        int __user                      *addr_len;
        int                             flags;
        unsigned long                   nofile;
};

struct io_sync {
        struct file                     *file;
        loff_t                          len;
        loff_t                          off;
        int                             flags;
        int                             mode;
};

struct io_cancel {
        struct file                     *file;
        u64                             addr;
};

struct io_timeout {
        struct file                     *file;
        u32                             off;
        u32                             target_seq;
        struct list_head                list;
        /* head of the link, used by linked timeouts only */
        struct io_kiocb                 *head;
};

struct io_timeout_rem {
        struct file                     *file;
        u64                             addr;

        /* timeout update */
        struct timespec64               ts;
        u32                             flags;
};

struct io_rw {
        /* NOTE: kiocb has the file as the first member, so don't do it here */
        struct kiocb                    kiocb;
        u64                             addr;
        u64                             len;
};

struct io_connect {
        struct file                     *file;
        struct sockaddr __user          *addr;
        int                             addr_len;
};

struct io_sr_msg {
        struct file                     *file;
        union {
                struct compat_msghdr __user     *umsg_compat;
                struct user_msghdr __user       *umsg;
                void __user                     *buf;
        };
        int                             msg_flags;
        int                             bgid;
        size_t                          len;
        struct io_buffer                *kbuf;
};

struct io_open {
        struct file                     *file;
        int                             dfd;
        struct filename                 *filename;
        struct open_how                 how;
        unsigned long                   nofile;
};

struct io_rsrc_update {
        struct file                     *file;
        u64                             arg;
        u32                             nr_args;
        u32                             offset;
};

struct io_fadvise {
        struct file                     *file;
        u64                             offset;
        u32                             len;
        u32                             advice;
};

struct io_madvise {
        struct file                     *file;
        u64                             addr;
        u32                             len;
        u32                             advice;
};

struct io_epoll {
        struct file                     *file;
        int                             epfd;
        int                             op;
        int                             fd;
        struct epoll_event              event;
};

struct io_splice {
        struct file                     *file_out;
        struct file                     *file_in;
        loff_t                          off_out;
        loff_t                          off_in;
        u64                             len;
        unsigned int                    flags;
};

struct io_provide_buf {
        struct file                     *file;
        __u64                           addr;
        __u32                           len;
        __u32                           bgid;
        __u16                           nbufs;
        __u16                           bid;
};

struct io_statx {
        struct file                     *file;
        int                             dfd;
        unsigned int                    mask;
        unsigned int                    flags;
        const char __user               *filename;
        struct statx __user             *buffer;
};

struct io_shutdown {
        struct file                     *file;
        int                             how;
};

struct io_rename {
        struct file                     *file;
        int                             old_dfd;
        int                             new_dfd;
        struct filename                 *oldpath;
        struct filename                 *newpath;
        int                             flags;
};

struct io_unlink {
        struct file                     *file;
        int                             dfd;
        int                             flags;
        struct filename                 *filename;
};

struct io_completion {
        struct file                     *file;
        struct list_head                list;
        u32                             cflags;
};

struct io_async_connect {
        struct sockaddr_storage         address;
};

struct io_async_msghdr {
        struct iovec                    fast_iov[UIO_FASTIOV];
        /* points to an allocated iov, if NULL we use fast_iov instead */
        struct iovec                    *free_iov;
        struct sockaddr __user          *uaddr;
        struct msghdr                   msg;
        struct sockaddr_storage         addr;
};

struct io_async_rw {
        struct iovec                    fast_iov[UIO_FASTIOV];
        const struct iovec              *free_iovec;
        struct iov_iter                 iter;
        size_t                          bytes_done;
        struct wait_page_queue          wpq;
};

enum {
        REQ_F_FIXED_FILE_BIT    = IOSQE_FIXED_FILE_BIT,
        REQ_F_IO_DRAIN_BIT      = IOSQE_IO_DRAIN_BIT,
        REQ_F_LINK_BIT          = IOSQE_IO_LINK_BIT,
        REQ_F_HARDLINK_BIT      = IOSQE_IO_HARDLINK_BIT,
        REQ_F_FORCE_ASYNC_BIT   = IOSQE_ASYNC_BIT,
        REQ_F_BUFFER_SELECT_BIT = IOSQE_BUFFER_SELECT_BIT,

        /* first byte is taken by user flags, shift it to not overlap */
        REQ_F_FAIL_BIT          = 8,
        REQ_F_INFLIGHT_BIT,
        REQ_F_CUR_POS_BIT,
        REQ_F_NOWAIT_BIT,
        REQ_F_LINK_TIMEOUT_BIT,
        REQ_F_NEED_CLEANUP_BIT,
        REQ_F_POLLED_BIT,
        REQ_F_BUFFER_SELECTED_BIT,
        REQ_F_LTIMEOUT_ACTIVE_BIT,
        REQ_F_COMPLETE_INLINE_BIT,
        REQ_F_REISSUE_BIT,
        REQ_F_DONT_REISSUE_BIT,
        REQ_F_CREDS_BIT,
        /* keep async read/write and isreg together and in order */
        REQ_F_ASYNC_READ_BIT,
        REQ_F_ASYNC_WRITE_BIT,
        REQ_F_ISREG_BIT,

        /* not a real bit, just to check we're not overflowing the space */
        __REQ_F_LAST_BIT,
};

enum {
        /* ctx owns file */
        REQ_F_FIXED_FILE        = BIT(REQ_F_FIXED_FILE_BIT),
        /* drain existing IO first */
        REQ_F_IO_DRAIN          = BIT(REQ_F_IO_DRAIN_BIT),
        /* linked sqes */
        REQ_F_LINK              = BIT(REQ_F_LINK_BIT),
        /* doesn't sever on completion < 0 */
        REQ_F_HARDLINK          = BIT(REQ_F_HARDLINK_BIT),
        /* IOSQE_ASYNC */
        REQ_F_FORCE_ASYNC       = BIT(REQ_F_FORCE_ASYNC_BIT),
        /* IOSQE_BUFFER_SELECT */
        REQ_F_BUFFER_SELECT     = BIT(REQ_F_BUFFER_SELECT_BIT),

        /* fail rest of links */
        REQ_F_FAIL              = BIT(REQ_F_FAIL_BIT),
        /* on inflight list, should be cancelled and waited on exit reliably */
        REQ_F_INFLIGHT          = BIT(REQ_F_INFLIGHT_BIT),
        /* read/write uses file position */
        REQ_F_CUR_POS           = BIT(REQ_F_CUR_POS_BIT),
        /* must not punt to workers */
        REQ_F_NOWAIT            = BIT(REQ_F_NOWAIT_BIT),
        /* has or had linked timeout */
        REQ_F_LINK_TIMEOUT      = BIT(REQ_F_LINK_TIMEOUT_BIT),
        /* needs cleanup */
        REQ_F_NEED_CLEANUP      = BIT(REQ_F_NEED_CLEANUP_BIT),
        /* already went through poll handler */
        REQ_F_POLLED            = BIT(REQ_F_POLLED_BIT),
        /* buffer already selected */
        REQ_F_BUFFER_SELECTED   = BIT(REQ_F_BUFFER_SELECTED_BIT),
        /* linked timeout is active, i.e. prepared by link's head */
        REQ_F_LTIMEOUT_ACTIVE   = BIT(REQ_F_LTIMEOUT_ACTIVE_BIT),
        /* completion is deferred through io_comp_state */
        REQ_F_COMPLETE_INLINE   = BIT(REQ_F_COMPLETE_INLINE_BIT),
        /* caller should reissue async */
        REQ_F_REISSUE           = BIT(REQ_F_REISSUE_BIT),
        /* don't attempt request reissue, see io_rw_reissue() */
        REQ_F_DONT_REISSUE      = BIT(REQ_F_DONT_REISSUE_BIT),
        /* supports async reads */
        REQ_F_ASYNC_READ        = BIT(REQ_F_ASYNC_READ_BIT),
        /* supports async writes */
        REQ_F_ASYNC_WRITE       = BIT(REQ_F_ASYNC_WRITE_BIT),
        /* regular file */
        REQ_F_ISREG             = BIT(REQ_F_ISREG_BIT),
        /* has creds assigned */
        REQ_F_CREDS             = BIT(REQ_F_CREDS_BIT),
};

struct async_poll {
        struct io_poll_iocb     poll;
        struct io_poll_iocb     *double_poll;
};

typedef void (*io_req_tw_func_t)(struct io_kiocb *req);

struct io_task_work {
        union {
                struct io_wq_work_node  node;
                struct llist_node       fallback_node;
        };
        io_req_tw_func_t                func;
};

enum {
        IORING_RSRC_FILE                = 0,
        IORING_RSRC_BUFFER              = 1,
};

/*
 * NOTE! Each of the iocb union members has the file pointer
 * as the first entry in their struct definition. So you can
 * access the file pointer through any of the sub-structs,
 * or directly as just 'ki_filp' in this struct.
 */
struct io_kiocb {
        union {
                struct file             *file;
                struct io_rw            rw;
                struct io_poll_iocb     poll;
                struct io_poll_update   poll_update;
                struct io_accept        accept;
                struct io_sync          sync;
                struct io_cancel        cancel;
                struct io_timeout       timeout;
                struct io_timeout_rem   timeout_rem;
                struct io_connect       connect;
                struct io_sr_msg        sr_msg;
                struct io_open          open;
                struct io_close         close;
                struct io_rsrc_update   rsrc_update;
                struct io_fadvise       fadvise;
                struct io_madvise       madvise;
                struct io_epoll         epoll;
                struct io_splice        splice;
                struct io_provide_buf   pbuf;
                struct io_statx         statx;
                struct io_shutdown      shutdown;
                struct io_rename        rename;
                struct io_unlink        unlink;
                /* use only after cleaning per-op data, see io_clean_op() */
                struct io_completion    compl;
        };

        /* opcode allocated if it needs to store data for async defer */
        void                            *async_data;
        u8                              opcode;
        /* polled IO has completed */
        u8                              iopoll_completed;

        u16                             buf_index;
        u32                             result;

        struct io_ring_ctx              *ctx;
        unsigned int                    flags;
        atomic_t                        refs;
        struct task_struct              *task;
        u64                             user_data;

        struct io_kiocb                 *link;
        struct percpu_ref               *fixed_rsrc_refs;

        /* used with ctx->iopoll_list with reads/writes */
        struct list_head                inflight_entry;
        struct io_task_work             io_task_work;
        /* for polled requests, i.e. IORING_OP_POLL_ADD and async armed poll */
        struct hlist_node               hash_node;
        struct async_poll               *apoll;
        struct io_wq_work               work;
        const struct cred               *creds;

        /* store used ubuf, so we can prevent reloading */
        struct io_mapped_ubuf           *imu;
};

struct io_tctx_node {
        struct list_head        ctx_node;
        struct task_struct      *task;
        struct io_ring_ctx      *ctx;
};

struct io_defer_entry {
        struct list_head        list;
        struct io_kiocb         *req;
        u32                     seq;
};

struct io_op_def {
        /* needs req->file assigned */
        unsigned                needs_file : 1;
        /* hash wq insertion if file is a regular file */
        unsigned                hash_reg_file : 1;
        /* unbound wq insertion if file is a non-regular file */
        unsigned                unbound_nonreg_file : 1;
        /* opcode is not supported by this kernel */
        unsigned                not_supported : 1;
        /* set if opcode supports polled "wait" */
        unsigned                pollin : 1;
        unsigned                pollout : 1;
        /* op supports buffer selection */
        unsigned                buffer_select : 1;
        /* do prep async if is going to be punted */
        unsigned                needs_async_setup : 1;
        /* should block plug */
        unsigned                plug : 1;
        /* size of async data needed, if any */
        unsigned short          async_size;
};

static const struct io_op_def io_op_defs[] = {
        [IORING_OP_NOP] = {},
        [IORING_OP_READV] = {
                .needs_file             = 1,
                .unbound_nonreg_file    = 1,
                .pollin                 = 1,
                .buffer_select          = 1,
                .needs_async_setup      = 1,
                .plug                   = 1,
                .async_size             = sizeof(struct io_async_rw),
        },
        [IORING_OP_WRITEV] = {
                .needs_file             = 1,
                .hash_reg_file          = 1,
                .unbound_nonreg_file    = 1,
                .pollout                = 1,
                .needs_async_setup      = 1,
                .plug                   = 1,
                .async_size             = sizeof(struct io_async_rw),
        },
        [IORING_OP_FSYNC] = {
                .needs_file             = 1,
        },
        [IORING_OP_READ_FIXED] = {
                .needs_file             = 1,
                .unbound_nonreg_file    = 1,
                .pollin                 = 1,
                .plug                   = 1,
                .async_size             = sizeof(struct io_async_rw),
        },
        [IORING_OP_WRITE_FIXED] = {
                .needs_file             = 1,
                .hash_reg_file          = 1,
                .unbound_nonreg_file    = 1,
                .pollout                = 1,
                .plug                   = 1,
                .async_size             = sizeof(struct io_async_rw),
        },
        [IORING_OP_POLL_ADD] = {
                .needs_file             = 1,
                .unbound_nonreg_file    = 1,
        },
        [IORING_OP_POLL_REMOVE] = {},
        [IORING_OP_SYNC_FILE_RANGE] = {
                .needs_file             = 1,
        },
        [IORING_OP_SENDMSG] = {
                .needs_file             = 1,
                .unbound_nonreg_file    = 1,
                .pollout                = 1,
                .needs_async_setup      = 1,
                .async_size             = sizeof(struct io_async_msghdr),
        },
        [IORING_OP_RECVMSG] = {
                .needs_file             = 1,
                .unbound_nonreg_file    = 1,
                .pollin                 = 1,
                .buffer_select          = 1,
                .needs_async_setup      = 1,
                .async_size             = sizeof(struct io_async_msghdr),
        },
        [IORING_OP_TIMEOUT] = {
                .async_size             = sizeof(struct io_timeout_data),
        },
        [IORING_OP_TIMEOUT_REMOVE] = {
                /* used by timeout updates' prep() */
        },
        [IORING_OP_ACCEPT] = {
                .needs_file             = 1,
                .unbound_nonreg_file    = 1,
                .pollin                 = 1,
        },
        [IORING_OP_ASYNC_CANCEL] = {},
        [IORING_OP_LINK_TIMEOUT] = {
                .async_size             = sizeof(struct io_timeout_data),
        },
        [IORING_OP_CONNECT] = {
                .needs_file             = 1,
                .unbound_nonreg_file    = 1,
                .pollout                = 1,
                .needs_async_setup      = 1,
                .async_size             = sizeof(struct io_async_connect),
        },
        [IORING_OP_FALLOCATE] = {
                .needs_file             = 1,
        },
        [IORING_OP_OPENAT] = {},
        [IORING_OP_CLOSE] = {},
        [IORING_OP_FILES_UPDATE] = {},
        [IORING_OP_STATX] = {},
        [IORING_OP_READ] = {
                .needs_file             = 1,
                .unbound_nonreg_file    = 1,
                .pollin                 = 1,
                .buffer_select          = 1,
                .plug                   = 1,
                .async_size             = sizeof(struct io_async_rw),

        },
        [IORING_OP_WRITE] = {
                .needs_file             = 1,
                .unbound_nonreg_file    = 1,
                .pollout                = 1,
                .plug                   = 1,
                .async_size             = sizeof(struct io_async_rw),
        },
        [IORING_OP_FADVISE] = {
                .needs_file             = 1,
        },
        [IORING_OP_MADVISE] = {},
        [IORING_OP_SEND] = {
                .needs_file             = 1,
                .unbound_nonreg_file    = 1,
                .pollout                = 1,
        },
        [IORING_OP_RECV] = {
                .needs_file             = 1,
                .unbound_nonreg_file    = 1,
                .pollin                 = 1,
                .buffer_select          = 1,
        },
        [IORING_OP_OPENAT2] = {
        },
        [IORING_OP_EPOLL_CTL] = {
                .unbound_nonreg_file    = 1,
        },
        [IORING_OP_SPLICE] = {
                .needs_file             = 1,
                .hash_reg_file          = 1,
                .unbound_nonreg_file    = 1,
        },
        [IORING_OP_PROVIDE_BUFFERS] = {},
        [IORING_OP_REMOVE_BUFFERS] = {},
        [IORING_OP_TEE] = {
                .needs_file             = 1,
                .hash_reg_file          = 1,
                .unbound_nonreg_file    = 1,
        },
        [IORING_OP_SHUTDOWN] = {
                .needs_file             = 1,
        },
        [IORING_OP_RENAMEAT] = {},
        [IORING_OP_UNLINKAT] = {},
};

static bool io_disarm_next(struct io_kiocb *req);
static void io_uring_del_tctx_node(unsigned long index);
static void io_uring_try_cancel_requests(struct io_ring_ctx *ctx,
                                         struct task_struct *task,
                                         bool cancel_all);
static void io_uring_cancel_generic(bool cancel_all, struct io_sq_data *sqd);
static struct io_rsrc_node *io_rsrc_node_alloc(struct io_ring_ctx *ctx);

static bool io_cqring_fill_event(struct io_ring_ctx *ctx, u64 user_data,
                                 long res, unsigned int cflags);
static void io_put_req(struct io_kiocb *req);
static void io_put_req_deferred(struct io_kiocb *req, int nr);
static void io_dismantle_req(struct io_kiocb *req);
static void io_put_task(struct task_struct *task, int nr);
static struct io_kiocb *io_prep_linked_timeout(struct io_kiocb *req);
static void io_queue_linked_timeout(struct io_kiocb *req);
static int __io_register_rsrc_update(struct io_ring_ctx *ctx, unsigned type,
                                     struct io_uring_rsrc_update2 *up,
                                     unsigned nr_args);
static void io_clean_op(struct io_kiocb *req);
static struct file *io_file_get(struct io_submit_state *state,
                                struct io_kiocb *req, int fd, bool fixed);
static void __io_queue_sqe(struct io_kiocb *req);
static void io_rsrc_put_work(struct work_struct *work);

static void io_req_task_queue(struct io_kiocb *req);
static void io_submit_flush_completions(struct io_ring_ctx *ctx);
static bool io_poll_remove_waitqs(struct io_kiocb *req);
static int io_req_prep_async(struct io_kiocb *req);

static void io_fallback_req_func(struct work_struct *unused);

static struct kmem_cache *req_cachep;

static const struct file_operations io_uring_fops;

struct sock *io_uring_get_socket(struct file *file)
{
#if defined(CONFIG_UNIX)
        if (file->f_op == &io_uring_fops) {
                struct io_ring_ctx *ctx = file->private_data;

                return ctx->ring_sock->sk;
        }
#endif
        return NULL;
}
EXPORT_SYMBOL(io_uring_get_socket);

#define io_for_each_link(pos, head) \
        for (pos = (head); pos; pos = pos->link)

static inline void io_req_set_rsrc_node(struct io_kiocb *req)
{
        struct io_ring_ctx *ctx = req->ctx;

        if (!req->fixed_rsrc_refs) {
                req->fixed_rsrc_refs = &ctx->rsrc_node->refs;
                percpu_ref_get(req->fixed_rsrc_refs);
        }
}

static void io_refs_resurrect(struct percpu_ref *ref, struct completion *compl)
{
        bool got = percpu_ref_tryget(ref);

        /* already at zero, wait for ->release() */
        if (!got)
                wait_for_completion(compl);
        percpu_ref_resurrect(ref);
        if (got)
                percpu_ref_put(ref);
}

static bool io_match_task(struct io_kiocb *head, struct task_struct *task,
                          bool cancel_all)
{
        struct io_kiocb *req;

        if (task && head->task != task)
                return false;
        if (cancel_all)
                return true;

        io_for_each_link(req, head) {
                if (req->flags & REQ_F_INFLIGHT)
                        return true;
        }
        return false;
}

static inline void req_set_fail(struct io_kiocb *req)
{
        req->flags |= REQ_F_FAIL;
}

static void io_ring_ctx_ref_free(struct percpu_ref *ref)
{
        struct io_ring_ctx *ctx = container_of(ref, struct io_ring_ctx, refs);

        complete(&ctx->ref_comp);
}

static inline bool io_is_timeout_noseq(struct io_kiocb *req)
{
        return !req->timeout.off;
}

static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
{
        struct io_ring_ctx *ctx;
        int hash_bits;

        ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
        if (!ctx)
                return NULL;

        /*
         * Use 5 bits less than the max cq entries, that should give us around
         * 32 entries per hash list if totally full and uniformly spread.
         */
        hash_bits = ilog2(p->cq_entries);
        hash_bits -= 5;
        if (hash_bits <= 0)
                hash_bits = 1;
        ctx->cancel_hash_bits = hash_bits;
        ctx->cancel_hash = kmalloc((1U << hash_bits) * sizeof(struct hlist_head),
                                        GFP_KERNEL);
        if (!ctx->cancel_hash)
                goto err;
        __hash_init(ctx->cancel_hash, 1U << hash_bits);

        ctx->dummy_ubuf = kzalloc(sizeof(*ctx->dummy_ubuf), GFP_KERNEL);
        if (!ctx->dummy_ubuf)
                goto err;
        /* set invalid range, so io_import_fixed() fails meeting it */
        ctx->dummy_ubuf->ubuf = -1UL;

        if (percpu_ref_init(&ctx->refs, io_ring_ctx_ref_free,
                            PERCPU_REF_ALLOW_REINIT, GFP_KERNEL))
                goto err;

        ctx->flags = p->flags;
        init_waitqueue_head(&ctx->sqo_sq_wait);
        INIT_LIST_HEAD(&ctx->sqd_list);
        init_waitqueue_head(&ctx->poll_wait);
        INIT_LIST_HEAD(&ctx->cq_overflow_list);
        init_completion(&ctx->ref_comp);
        xa_init_flags(&ctx->io_buffers, XA_FLAGS_ALLOC1);
        xa_init_flags(&ctx->personalities, XA_FLAGS_ALLOC1);
        mutex_init(&ctx->uring_lock);
        init_waitqueue_head(&ctx->cq_wait);
        spin_lock_init(&ctx->completion_lock);
        INIT_LIST_HEAD(&ctx->iopoll_list);
        INIT_LIST_HEAD(&ctx->defer_list);
        INIT_LIST_HEAD(&ctx->timeout_list);
        spin_lock_init(&ctx->rsrc_ref_lock);
        INIT_LIST_HEAD(&ctx->rsrc_ref_list);
        INIT_DELAYED_WORK(&ctx->rsrc_put_work, io_rsrc_put_work);
        init_llist_head(&ctx->rsrc_put_llist);
        INIT_LIST_HEAD(&ctx->tctx_list);
        INIT_LIST_HEAD(&ctx->submit_state.comp.free_list);
        INIT_LIST_HEAD(&ctx->locked_free_list);
        INIT_DELAYED_WORK(&ctx->fallback_work, io_fallback_req_func);
        return ctx;
err:
        kfree(ctx->dummy_ubuf);
        kfree(ctx->cancel_hash);
        kfree(ctx);
        return NULL;
}

static void io_account_cq_overflow(struct io_ring_ctx *ctx)
{
        struct io_rings *r = ctx->rings;

        WRITE_ONCE(r->cq_overflow, READ_ONCE(r->cq_overflow) + 1);
        ctx->cq_extra--;
}

static bool req_need_defer(struct io_kiocb *req, u32 seq)
{
        if (unlikely(req->flags & REQ_F_IO_DRAIN)) {
                struct io_ring_ctx *ctx = req->ctx;

                return seq + READ_ONCE(ctx->cq_extra) != ctx->cached_cq_tail;
        }

        return false;
}

static void io_req_track_inflight(struct io_kiocb *req)
{
        if (!(req->flags & REQ_F_INFLIGHT)) {
                req->flags |= REQ_F_INFLIGHT;
                atomic_inc(&current->io_uring->inflight_tracked);
        }
}

static void io_prep_async_work(struct io_kiocb *req)
{
        const struct io_op_def *def = &io_op_defs[req->opcode];
        struct io_ring_ctx *ctx = req->ctx;

        if (!(req->flags & REQ_F_CREDS)) {
                req->flags |= REQ_F_CREDS;
                req->creds = get_current_cred();
        }

        req->work.list.next = NULL;
        req->work.flags = 0;
        if (req->flags & REQ_F_FORCE_ASYNC)
                req->work.flags |= IO_WQ_WORK_CONCURRENT;

        if (req->flags & REQ_F_ISREG) {
                if (def->hash_reg_file || (ctx->flags & IORING_SETUP_IOPOLL))
                        io_wq_hash_work(&req->work, file_inode(req->file));
        } else if (!req->file || !S_ISBLK(file_inode(req->file)->i_mode)) {
                if (def->unbound_nonreg_file)
                        req->work.flags |= IO_WQ_WORK_UNBOUND;
        }

        switch (req->opcode) {
        case IORING_OP_SPLICE:
        case IORING_OP_TEE:
                if (!S_ISREG(file_inode(req->splice.file_in)->i_mode))
                        req->work.flags |= IO_WQ_WORK_UNBOUND;
                break;
        }
}

static void io_prep_async_link(struct io_kiocb *req)
{
        struct io_kiocb *cur;

        if (req->flags & REQ_F_LINK_TIMEOUT) {
                struct io_ring_ctx *ctx = req->ctx;

                spin_lock_irq(&ctx->completion_lock);
                io_for_each_link(cur, req)
                        io_prep_async_work(cur);
                spin_unlock_irq(&ctx->completion_lock);
        } else {
                io_for_each_link(cur, req)
                        io_prep_async_work(cur);
        }
}

static void io_queue_async_work(struct io_kiocb *req)
{
        struct io_ring_ctx *ctx = req->ctx;
        struct io_kiocb *link = io_prep_linked_timeout(req);
        struct io_uring_task *tctx = req->task->io_uring;

        BUG_ON(!tctx);
        BUG_ON(!tctx->io_wq);

        /* init ->work of the whole link before punting */
        io_prep_async_link(req);

        /*
         * Not expected to happen, but if we do have a bug where this _can_
         * happen, catch it here and ensure the request is marked as
         * canceled. That will make io-wq go through the usual work cancel
         * procedure rather than attempt to run this request (or create a new
         * worker for it).
         */
        if (WARN_ON_ONCE(!same_thread_group(req->task, current)))
                req->work.flags |= IO_WQ_WORK_CANCEL;

        trace_io_uring_queue_async_work(ctx, io_wq_is_hashed(&req->work), req,
                                        &req->work, req->flags);
        io_wq_enqueue(tctx->io_wq, &req->work);
        if (link)
                io_queue_linked_timeout(link);
}

static void io_kill_timeout(struct io_kiocb *req, int status)
        __must_hold(&req->ctx->completion_lock)
{
        struct io_timeout_data *io = req->async_data;

        if (hrtimer_try_to_cancel(&io->timer) != -1) {
                atomic_set(&req->ctx->cq_timeouts,
                        atomic_read(&req->ctx->cq_timeouts) + 1);
                list_del_init(&req->timeout.list);
                io_cqring_fill_event(req->ctx, req->user_data, status, 0);
                io_put_req_deferred(req, 1);
        }
}

static void io_queue_deferred(struct io_ring_ctx *ctx)
{
        while (!list_empty(&ctx->defer_list)) {
                struct io_defer_entry *de = list_first_entry(&ctx->defer_list,
                                                struct io_defer_entry, list);

                if (req_need_defer(de->req, de->seq))
                        break;
                list_del_init(&de->list);
                io_req_task_queue(de->req);
                kfree(de);
        }
}

static void io_flush_timeouts(struct io_ring_ctx *ctx)
{
        u32 seq = ctx->cached_cq_tail - atomic_read(&ctx->cq_timeouts);

        while (!list_empty(&ctx->timeout_list)) {
                u32 events_needed, events_got;
                struct io_kiocb *req = list_first_entry(&ctx->timeout_list,
                                                struct io_kiocb, timeout.list);

                if (io_is_timeout_noseq(req))
                        break;

                /*
                 * Since seq can easily wrap around over time, subtract
                 * the last seq at which timeouts were flushed before comparing.
                 * Assuming not more than 2^31-1 events have happened since,
                 * these subtractions won't have wrapped, so we can check if
                 * target is in [last_seq, current_seq] by comparing the two.
                 */
                events_needed = req->timeout.target_seq - ctx->cq_last_tm_flush;
                events_got = seq - ctx->cq_last_tm_flush;
                if (events_got < events_needed)
                        break;

                list_del_init(&req->timeout.list);
                io_kill_timeout(req, 0);
        }
        ctx->cq_last_tm_flush = seq;
}

static void __io_commit_cqring_flush(struct io_ring_ctx *ctx)
{
        if (ctx->off_timeout_used)
                io_flush_timeouts(ctx);
        if (ctx->drain_active)
                io_queue_deferred(ctx);
}

static inline void io_commit_cqring(struct io_ring_ctx *ctx)
{
        if (unlikely(ctx->off_timeout_used || ctx->drain_active))
                __io_commit_cqring_flush(ctx);
        /* order cqe stores with ring update */
        smp_store_release(&ctx->rings->cq.tail, ctx->cached_cq_tail);
}

static inline bool io_sqring_full(struct io_ring_ctx *ctx)
{
        struct io_rings *r = ctx->rings;

        return READ_ONCE(r->sq.tail) - ctx->cached_sq_head == ctx->sq_entries;
}

static inline unsigned int __io_cqring_events(struct io_ring_ctx *ctx)
{
        return ctx->cached_cq_tail - READ_ONCE(ctx->rings->cq.head);
}

static inline struct io_uring_cqe *io_get_cqe(struct io_ring_ctx *ctx)
{
        struct io_rings *rings = ctx->rings;
        unsigned tail, mask = ctx->cq_entries - 1;

        /*
         * writes to the cq entry need to come after reading head; the
         * control dependency is enough as we're using WRITE_ONCE to
         * fill the cq entry
         */
        if (__io_cqring_events(ctx) == ctx->cq_entries)
                return NULL;

        tail = ctx->cached_cq_tail++;
        return &rings->cqes[tail & mask];
}

static inline bool io_should_trigger_evfd(struct io_ring_ctx *ctx)
{
        if (likely(!ctx->cq_ev_fd))
                return false;
        if (READ_ONCE(ctx->rings->cq_flags) & IORING_CQ_EVENTFD_DISABLED)
                return false;
        return !ctx->eventfd_async || io_wq_current_is_worker();
}

static void io_cqring_ev_posted(struct io_ring_ctx *ctx)
{
        /* see waitqueue_active() comment */
        smp_mb();

        if (waitqueue_active(&ctx->cq_wait))
                wake_up(&ctx->cq_wait);
        if (ctx->sq_data && waitqueue_active(&ctx->sq_data->wait))
                wake_up(&ctx->sq_data->wait);
        if (io_should_trigger_evfd(ctx))
                eventfd_signal(ctx->cq_ev_fd, 1);
        if (waitqueue_active(&ctx->poll_wait)) {
                wake_up_interruptible(&ctx->poll_wait);
                kill_fasync(&ctx->cq_fasync, SIGIO, POLL_IN);
        }
}

static void io_cqring_ev_posted_iopoll(struct io_ring_ctx *ctx)
{
        /* see waitqueue_active() comment */
        smp_mb();

        if (ctx->flags & IORING_SETUP_SQPOLL) {
                if (waitqueue_active(&ctx->cq_wait))
                        wake_up(&ctx->cq_wait);
        }
        if (io_should_trigger_evfd(ctx))
                eventfd_signal(ctx->cq_ev_fd, 1);
        if (waitqueue_active(&ctx->poll_wait)) {
                wake_up_interruptible(&ctx->poll_wait);
                kill_fasync(&ctx->cq_fasync, SIGIO, POLL_IN);
        }
}

/* Returns true if there are no backlogged entries after the flush */
static bool __io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force)
{
        unsigned long flags;
        bool all_flushed, posted;

        if (!force && __io_cqring_events(ctx) == ctx->cq_entries)
                return false;

        posted = false;
        spin_lock_irqsave(&ctx->completion_lock, flags);
        while (!list_empty(&ctx->cq_overflow_list)) {
                struct io_uring_cqe *cqe = io_get_cqe(ctx);
                struct io_overflow_cqe *ocqe;

                if (!cqe && !force)
                        break;
                ocqe = list_first_entry(&ctx->cq_overflow_list,
                                        struct io_overflow_cqe, list);
                if (cqe)
                        memcpy(cqe, &ocqe->cqe, sizeof(*cqe));
                else
                        io_account_cq_overflow(ctx);

                posted = true;
                list_del(&ocqe->list);
                kfree(ocqe);
        }

        all_flushed = list_empty(&ctx->cq_overflow_list);
        if (all_flushed) {
                clear_bit(0, &ctx->check_cq_overflow);
                WRITE_ONCE(ctx->rings->sq_flags,
                           ctx->rings->sq_flags & ~IORING_SQ_CQ_OVERFLOW);
        }

        if (posted)
                io_commit_cqring(ctx);
        spin_unlock_irqrestore(&ctx->completion_lock, flags);
        if (posted)
                io_cqring_ev_posted(ctx);
        return all_flushed;
}

static bool io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force)
{
        bool ret = true;

        if (test_bit(0, &ctx->check_cq_overflow)) {
                /* iopoll syncs against uring_lock, not completion_lock */
                if (ctx->flags & IORING_SETUP_IOPOLL)
                        mutex_lock(&ctx->uring_lock);
                ret = __io_cqring_overflow_flush(ctx, force);
                if (ctx->flags & IORING_SETUP_IOPOLL)
                        mutex_unlock(&ctx->uring_lock);
        }

        return ret;
}

/*
 * Shamelessly stolen from the mm implementation of page reference checking,
 * see commit f958d7b528b1 for details.
 */
#define req_ref_zero_or_close_to_overflow(req)  \
        ((unsigned int) atomic_read(&(req->refs)) + 127u <= 127u)

static inline bool req_ref_inc_not_zero(struct io_kiocb *req)
{
        return atomic_inc_not_zero(&req->refs);
}

static inline bool req_ref_sub_and_test(struct io_kiocb *req, int refs)
{
        WARN_ON_ONCE(req_ref_zero_or_close_to_overflow(req));
        return atomic_sub_and_test(refs, &req->refs);
}

static inline bool req_ref_put_and_test(struct io_kiocb *req)
{
        WARN_ON_ONCE(req_ref_zero_or_close_to_overflow(req));
        return atomic_dec_and_test(&req->refs);
}

static inline void req_ref_put(struct io_kiocb *req)
{
        WARN_ON_ONCE(req_ref_put_and_test(req));
}

static inline void req_ref_get(struct io_kiocb *req)
{
        WARN_ON_ONCE(req_ref_zero_or_close_to_overflow(req));
        atomic_inc(&req->refs);
}

static bool io_cqring_event_overflow(struct io_ring_ctx *ctx, u64 user_data,
                                     long res, unsigned int cflags)
{
        struct io_overflow_cqe *ocqe;

        ocqe = kmalloc(sizeof(*ocqe), GFP_ATOMIC | __GFP_ACCOUNT);
        if (!ocqe) {
                /*
                 * If we're in ring overflow flush mode, or in task cancel mode,
                 * or cannot allocate an overflow entry, then we need to drop it
                 * on the floor.
                 */
                io_account_cq_overflow(ctx);
                return false;
        }
        if (list_empty(&ctx->cq_overflow_list)) {
                set_bit(0, &ctx->check_cq_overflow);
                WRITE_ONCE(ctx->rings->sq_flags,
                           ctx->rings->sq_flags | IORING_SQ_CQ_OVERFLOW);

        }
        ocqe->cqe.user_data = user_data;
        ocqe->cqe.res = res;
        ocqe->cqe.flags = cflags;
        list_add_tail(&ocqe->list, &ctx->cq_overflow_list);
        return true;
}

static inline bool __io_cqring_fill_event(struct io_ring_ctx *ctx, u64 user_data,
                                          long res, unsigned int cflags)
{
        struct io_uring_cqe *cqe;

        trace_io_uring_complete(ctx, user_data, res, cflags);

        /*
         * If we can't get a cq entry, userspace overflowed the
         * submission (by quite a lot). Increment the overflow count in
         * the ring.
         */
        cqe = io_get_cqe(ctx);
        if (likely(cqe)) {
                WRITE_ONCE(cqe->user_data, user_data);
                WRITE_ONCE(cqe->res, res);
                WRITE_ONCE(cqe->flags, cflags);
                return true;
        }
        return io_cqring_event_overflow(ctx, user_data, res, cflags);
}

/* not as hot to bloat with inlining */
static noinline bool io_cqring_fill_event(struct io_ring_ctx *ctx, u64 user_data,
                                          long res, unsigned int cflags)
{
        return __io_cqring_fill_event(ctx, user_data, res, cflags);
}

static void io_req_complete_post(struct io_kiocb *req, long res,
                                 unsigned int cflags)
{
        struct io_ring_ctx *ctx = req->ctx;
        unsigned long flags;

        spin_lock_irqsave(&ctx->completion_lock, flags);
        __io_cqring_fill_event(ctx, req->user_data, res, cflags);
        /*
         * If we're the last reference to this request, add to our locked
         * free_list cache.
         */
        if (req_ref_put_and_test(req)) {
                if (req->flags & (REQ_F_LINK | REQ_F_HARDLINK)) {
                        if (req->flags & (REQ_F_LINK_TIMEOUT | REQ_F_FAIL))
                                io_disarm_next(req);
                        if (req->link) {
                                io_req_task_queue(req->link);
                                req->link = NULL;
                        }
                }
                io_dismantle_req(req);
                io_put_task(req->task, 1);
                list_add(&req->compl.list, &ctx->locked_free_list);
                ctx->locked_free_nr++;
        } else {
                if (!percpu_ref_tryget(&ctx->refs))
                        req = NULL;
        }
        io_commit_cqring(ctx);
        spin_unlock_irqrestore(&ctx->completion_lock, flags);

        if (req) {
                io_cqring_ev_posted(ctx);
                percpu_ref_put(&ctx->refs);
        }
}

static inline bool io_req_needs_clean(struct io_kiocb *req)
{
        return req->flags & IO_REQ_CLEAN_FLAGS;
}

static void io_req_complete_state(struct io_kiocb *req, long res,
                                  unsigned int cflags)
{
        if (io_req_needs_clean(req))
                io_clean_op(req);
        req->result = res;
        req->compl.cflags = cflags;
        req->flags |= REQ_F_COMPLETE_INLINE;
}

static inline void __io_req_complete(struct io_kiocb *req, unsigned issue_flags,
                                     long res, unsigned cflags)
{
        if (issue_flags & IO_URING_F_COMPLETE_DEFER)
                io_req_complete_state(req, res, cflags);
        else
                io_req_complete_post(req, res, cflags);
}

static inline void io_req_complete(struct io_kiocb *req, long res)
{
        __io_req_complete(req, 0, res, 0);
}

static void io_req_complete_failed(struct io_kiocb *req, long res)
{
        req_set_fail(req);
        io_put_req(req);
        io_req_complete_post(req, res, 0);
}

static void io_flush_cached_locked_reqs(struct io_ring_ctx *ctx,
                                        struct io_comp_state *cs)
{
        spin_lock_irq(&ctx->completion_lock);
        list_splice_init(&ctx->locked_free_list, &cs->free_list);
        ctx->locked_free_nr = 0;
        spin_unlock_irq(&ctx->completion_lock);
}

/* Returns true IFF there are requests in the cache */
static bool io_flush_cached_reqs(struct io_ring_ctx *ctx)
{
        struct io_submit_state *state = &ctx->submit_state;
        struct io_comp_state *cs = &state->comp;
        int nr;

        /*
         * If we have more than a batch's worth of requests in our IRQ side
         * locked cache, grab the lock and move them over to our submission
         * side cache.
         */
        if (READ_ONCE(ctx->locked_free_nr) > IO_COMPL_BATCH)
                io_flush_cached_locked_reqs(ctx, cs);

        nr = state->free_reqs;
        while (!list_empty(&cs->free_list)) {
                struct io_kiocb *req = list_first_entry(&cs->free_list,
                                                struct io_kiocb, compl.list);

                list_del(&req->compl.list);
                state->reqs[nr++] = req;
                if (nr == ARRAY_SIZE(state->reqs))
                        break;
        }

        state->free_reqs = nr;
        return nr != 0;
}

static struct io_kiocb *io_alloc_req(struct io_ring_ctx *ctx)
{
        struct io_submit_state *state = &ctx->submit_state;

        BUILD_BUG_ON(ARRAY_SIZE(state->reqs) < IO_REQ_ALLOC_BATCH);

        if (!state->free_reqs) {
                gfp_t gfp = GFP_KERNEL | __GFP_NOWARN;
                int ret, i;

                if (io_flush_cached_reqs(ctx))
                        goto got_req;

                ret = kmem_cache_alloc_bulk(req_cachep, gfp, IO_REQ_ALLOC_BATCH,
                                            state->reqs);

                /*
                 * Bulk alloc is all-or-nothing. If we fail to get a batch,
                 * retry single alloc to be on the safe side.
                 */
                if (unlikely(ret <= 0)) {
                        state->reqs[0] = kmem_cache_alloc(req_cachep, gfp);
                        if (!state->reqs[0])
                                return NULL;
                        ret = 1;
                }

                /*
                 * Don't initialise the fields below on every allocation, but
                 * do that in advance and keep valid on free.
                 */
                for (i = 0; i < ret; i++) {
                        struct io_kiocb *req = state->reqs[i];

                        req->ctx = ctx;
                        req->link = NULL;
                        req->async_data = NULL;
                        /* not necessary, but safer to zero */
                        req->result = 0;
                }
                state->free_reqs = ret;
        }
got_req:
        state->free_reqs--;
        return state->reqs[state->free_reqs];
}

static inline void io_put_file(struct file *file)
{
        if (file)
                fput(file);
}

static void io_dismantle_req(struct io_kiocb *req)
{
        unsigned int flags = req->flags;

        if (io_req_needs_clean(req))
                io_clean_op(req);
        if (!(flags & REQ_F_FIXED_FILE))
                io_put_file(req->file);
        if (req->fixed_rsrc_refs)
                percpu_ref_put(req->fixed_rsrc_refs);
        if (req->async_data) {
                kfree(req->async_data);
                req->async_data = NULL;
        }
}

/* must to be called somewhat shortly after putting a request */
static inline void io_put_task(struct task_struct *task, int nr)
{
        struct io_uring_task *tctx = task->io_uring;

        percpu_counter_sub(&tctx->inflight, nr);
        if (unlikely(atomic_read(&tctx->in_idle)))
                wake_up(&tctx->wait);
        put_task_struct_many(task, nr);
}

static void __io_free_req(struct io_kiocb *req)
{
        struct io_ring_ctx *ctx = req->ctx;

        io_dismantle_req(req);
        io_put_task(req->task, 1);

        kmem_cache_free(req_cachep, req);
        percpu_ref_put(&ctx->refs);
}

static inline void io_remove_next_linked(struct io_kiocb *req)
{
        struct io_kiocb *nxt = req->link;

        req->link = nxt->link;
        nxt->link = NULL;
}

static bool io_kill_linked_timeout(struct io_kiocb *req)
        __must_hold(&req->ctx->completion_lock)
{
        struct io_kiocb *link = req->link;

        /*
         * Can happen if a linked timeout fired and link had been like
         * req -> link t-out -> link t-out [-> ...]
         */
        if (link && (link->flags & REQ_F_LTIMEOUT_ACTIVE)) {
                struct io_timeout_data *io = link->async_data;

                io_remove_next_linked(req);
                link->timeout.head = NULL;
                if (hrtimer_try_to_cancel(&io->timer) != -1) {
                        io_cqring_fill_event(link->ctx, link->user_data,
                                             -ECANCELED, 0);
                        io_put_req_deferred(link, 1);
                        return true;
                }
        }
        return false;
}

static void io_fail_links(struct io_kiocb *req)
        __must_hold(&req->ctx->completion_lock)
{
        struct io_kiocb *nxt, *link = req->link;

        req->link = NULL;
        while (link) {
                nxt = link->link;
                link->link = NULL;

                trace_io_uring_fail_link(req, link);
                io_cqring_fill_event(link->ctx, link->user_data, -ECANCELED, 0);
                io_put_req_deferred(link, 2);
                link = nxt;
        }
}

static bool io_disarm_next(struct io_kiocb *req)
        __must_hold(&req->ctx->completion_lock)
{
        bool posted = false;

        if (likely(req->flags & REQ_F_LINK_TIMEOUT))
                posted = io_kill_linked_timeout(req);
        if (unlikely((req->flags & REQ_F_FAIL) &&
                     !(req->flags & REQ_F_HARDLINK))) {
                posted |= (req->link != NULL);
                io_fail_links(req);
        }
        return posted;
}

static struct io_kiocb *__io_req_find_next(struct io_kiocb *req)
{
        struct io_kiocb *nxt;

        /*
         * If LINK is set, we have dependent requests in this chain. If we
         * didn't fail this request, queue the first one up, moving any other
         * dependencies to the next request. In case of failure, fail the rest
         * of the chain.
         */
        if (req->flags & (REQ_F_LINK_TIMEOUT | REQ_F_FAIL)) {
                struct io_ring_ctx *ctx = req->ctx;
                unsigned long flags;
                bool posted;

                spin_lock_irqsave(&ctx->completion_lock, flags);
                posted = io_disarm_next(req);
                if (posted)
                        io_commit_cqring(req->ctx);
                spin_unlock_irqrestore(&ctx->completion_lock, flags);
                if (posted)
                        io_cqring_ev_posted(ctx);
        }
        nxt = req->link;
        req->link = NULL;
        return nxt;
}

static inline struct io_kiocb *io_req_find_next(struct io_kiocb *req)
{
        if (likely(!(req->flags & (REQ_F_LINK|REQ_F_HARDLINK))))
                return NULL;
        return __io_req_find_next(req);
}

static void ctx_flush_and_put(struct io_ring_ctx *ctx)
{
        if (!ctx)
                return;
        if (ctx->submit_state.comp.nr) {
                mutex_lock(&ctx->uring_lock);
                io_submit_flush_completions(ctx);
                mutex_unlock(&ctx->uring_lock);
        }
        percpu_ref_put(&ctx->refs);
}

static void tctx_task_work(struct callback_head *cb)
{
        struct io_ring_ctx *ctx = NULL;
        struct io_uring_task *tctx = container_of(cb, struct io_uring_task,
                                                  task_work);

        while (1) {
                struct io_wq_work_node *node;

                spin_lock_irq(&tctx->task_lock);
                node = tctx->task_list.first;
                INIT_WQ_LIST(&tctx->task_list);
                spin_unlock_irq(&tctx->task_lock);

                while (node) {
                        struct io_wq_work_node *next = node->next;
                        struct io_kiocb *req = container_of(node, struct io_kiocb,
                                                            io_task_work.node);

                        if (req->ctx != ctx) {
                                ctx_flush_and_put(ctx);
                                ctx = req->ctx;
                                percpu_ref_get(&ctx->refs);
                        }
                        req->io_task_work.func(req);
                        node = next;
                }
                if (wq_list_empty(&tctx->task_list)) {
                        spin_lock_irq(&tctx->task_lock);
                        clear_bit(0, &tctx->task_state);
                        if (wq_list_empty(&tctx->task_list)) {
                                spin_unlock_irq(&tctx->task_lock);
                                break;
                        }
                        spin_unlock_irq(&tctx->task_lock);
                        /* another tctx_task_work() is enqueued, yield */
                        if (test_and_set_bit(0, &tctx->task_state))
                                break;
                }
                cond_resched();
        }

        ctx_flush_and_put(ctx);
}

static void io_req_task_work_add(struct io_kiocb *req)
{
        struct task_struct *tsk = req->task;
        struct io_uring_task *tctx = tsk->io_uring;
        enum task_work_notify_mode notify;
        struct io_wq_work_node *node;
        unsigned long flags;

        WARN_ON_ONCE(!tctx);

        spin_lock_irqsave(&tctx->task_lock, flags);
        wq_list_add_tail(&req->io_task_work.node, &tctx->task_list);
        spin_unlock_irqrestore(&tctx->task_lock, flags);

        /* task_work already pending, we're done */
        if (test_bit(0, &tctx->task_state) ||
            test_and_set_bit(0, &tctx->task_state))
                return;

        if (unlikely(tsk->flags & PF_EXITING))
                goto fail;

        /*
         * SQPOLL kernel thread doesn't need notification, just a wakeup. For
         * all other cases, use TWA_SIGNAL unconditionally to ensure we're
         * processing task_work. There's no reliable way to tell if TWA_RESUME
         * will do the job.
         */
        notify = (req->ctx->flags & IORING_SETUP_SQPOLL) ? TWA_NONE : TWA_SIGNAL;
        if (!task_work_add(tsk, &tctx->task_work, notify)) {
                wake_up_process(tsk);
                return;
        }
fail:
        clear_bit(0, &tctx->task_state);
        spin_lock_irqsave(&tctx->task_lock, flags);
        node = tctx->task_list.first;
        INIT_WQ_LIST(&tctx->task_list);
        spin_unlock_irqrestore(&tctx->task_lock, flags);

        while (node) {
                req = container_of(node, struct io_kiocb, io_task_work.node);
                node = node->next;
                if (llist_add(&req->io_task_work.fallback_node,
                              &req->ctx->fallback_llist))
                        schedule_delayed_work(&req->ctx->fallback_work, 1);
        }
}

static void io_req_task_cancel(struct io_kiocb *req)
{
        struct io_ring_ctx *ctx = req->ctx;

        /* ctx is guaranteed to stay alive while we hold uring_lock */
        mutex_lock(&ctx->uring_lock);
        io_req_complete_failed(req, req->result);
        mutex_unlock(&ctx->uring_lock);
}

static void io_req_task_submit(struct io_kiocb *req)
{
        struct io_ring_ctx *ctx = req->ctx;

        /* ctx stays valid until unlock, even if we drop all ours ctx->refs */
        mutex_lock(&ctx->uring_lock);
        if (!(req->task->flags & PF_EXITING) && !req->task->in_execve)
                __io_queue_sqe(req);
        else
                io_req_complete_failed(req, -EFAULT);
        mutex_unlock(&ctx->uring_lock);
}

static void io_req_task_queue_fail(struct io_kiocb *req, int ret)
{
        req->result = ret;
        req->io_task_work.func = io_req_task_cancel;
        io_req_task_work_add(req);
}

static void io_req_task_queue(struct io_kiocb *req)
{
        req->io_task_work.func = io_req_task_submit;
        io_req_task_work_add(req);
}

static void io_req_task_queue_reissue(struct io_kiocb *req)
{
        req->io_task_work.func = io_queue_async_work;
        io_req_task_work_add(req);
}

static inline void io_queue_next(struct io_kiocb *req)
{
        struct io_kiocb *nxt = io_req_find_next(req);

        if (nxt)
                io_req_task_queue(nxt);
}

static void io_free_req(struct io_kiocb *req)
{
        io_queue_next(req);
        __io_free_req(req);
}

struct req_batch {
        struct task_struct      *task;
        int                     task_refs;
        int                     ctx_refs;
};

static inline void io_init_req_batch(struct req_batch *rb)
{
        rb->task_refs = 0;
        rb->ctx_refs = 0;
        rb->task = NULL;
}

static void io_req_free_batch_finish(struct io_ring_ctx *ctx,
                                     struct req_batch *rb)
{
        if (rb->task)
                io_put_task(rb->task, rb->task_refs);
        if (rb->ctx_refs)
                percpu_ref_put_many(&ctx->refs, rb->ctx_refs);
}

static void io_req_free_batch(struct req_batch *rb, struct io_kiocb *req,
                              struct io_submit_state *state)
{
        io_queue_next(req);
        io_dismantle_req(req);

        if (req->task != rb->task) {
                if (rb->task)
                        io_put_task(rb->task, rb->task_refs);
                rb->task = req->task;
                rb->task_refs = 0;
        }
        rb->task_refs++;
        rb->ctx_refs++;

        if (state->free_reqs != ARRAY_SIZE(state->reqs))
                state->reqs[state->free_reqs++] = req;
        else
                list_add(&req->compl.list, &state->comp.free_list);
}

static void io_submit_flush_completions(struct io_ring_ctx *ctx)
{
        struct io_comp_state *cs = &ctx->submit_state.comp;
        int i, nr = cs->nr;
        struct req_batch rb;

        spin_lock_irq(&ctx->completion_lock);
        for (i = 0; i < nr; i++) {
                struct io_kiocb *req = cs->reqs[i];

                __io_cqring_fill_event(ctx, req->user_data, req->result,
                                        req->compl.cflags);
        }
        io_commit_cqring(ctx);
        spin_unlock_irq(&ctx->completion_lock);
        io_cqring_ev_posted(ctx);

        io_init_req_batch(&rb);
        for (i = 0; i < nr; i++) {
                struct io_kiocb *req = cs->reqs[i];

                /* submission and completion refs */
                if (req_ref_sub_and_test(req, 2))
                        io_req_free_batch(&rb, req, &ctx->submit_state);
        }

        io_req_free_batch_finish(ctx, &rb);
        cs->nr = 0;
}

/*
 * Drop reference to request, return next in chain (if there is one) if this
 * was the last reference to this request.
 */
static inline struct io_kiocb *io_put_req_find_next(struct io_kiocb *req)
{
        struct io_kiocb *nxt = NULL;

        if (req_ref_put_and_test(req)) {
                nxt = io_req_find_next(req);
                __io_free_req(req);
        }
        return nxt;
}

static inline void io_put_req(struct io_kiocb *req)
{
        if (req_ref_put_and_test(req))
                io_free_req(req);
}

static void io_free_req_deferred(struct io_kiocb *req)
{
        req->io_task_work.func = io_free_req;
        io_req_task_work_add(req);
}

static inline void io_put_req_deferred(struct io_kiocb *req, int refs)
{
        if (req_ref_sub_and_test(req, refs))
                io_free_req_deferred(req);
}

static unsigned io_cqring_events(struct io_ring_ctx *ctx)
{
        /* See comment at the top of this file */
        smp_rmb();
        return __io_cqring_events(ctx);
}

static inline unsigned int io_sqring_entries(struct io_ring_ctx *ctx)
{
        struct io_rings *rings = ctx->rings;

        /* make sure SQ entry isn't read before tail */
        return smp_load_acquire(&rings->sq.tail) - ctx->cached_sq_head;
}

static unsigned int io_put_kbuf(struct io_kiocb *req, struct io_buffer *kbuf)
{
        unsigned int cflags;

        cflags = kbuf->bid << IORING_CQE_BUFFER_SHIFT;
        cflags |= IORING_CQE_F_BUFFER;
        req->flags &= ~REQ_F_BUFFER_SELECTED;
        kfree(kbuf);
        return cflags;
}

static inline unsigned int io_put_rw_kbuf(struct io_kiocb *req)
{
        struct io_buffer *kbuf;

        kbuf = (struct io_buffer *) (unsigned long) req->rw.addr;
        return io_put_kbuf(req, kbuf);
}

static inline bool io_run_task_work(void)
{
        if (test_thread_flag(TIF_NOTIFY_SIGNAL) || current->task_works) {
                __set_current_state(TASK_RUNNING);
                tracehook_notify_signal();
                return true;
        }

        return false;
}

/*
 * Find and free completed poll iocbs
 */
static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
                               struct list_head *done, bool resubmit)
{
        struct req_batch rb;
        struct io_kiocb *req;

        /* order with ->result store in io_complete_rw_iopoll() */
        smp_rmb();

        io_init_req_batch(&rb);
        while (!list_empty(done)) {
                int cflags = 0;

                req = list_first_entry(done, struct io_kiocb, inflight_entry);
                list_del(&req->inflight_entry);

                if (READ_ONCE(req->result) == -EAGAIN && resubmit &&
                    !(req->flags & REQ_F_DONT_REISSUE)) {
                        req->iopoll_completed = 0;
                        req_ref_get(req);
                        io_req_task_queue_reissue(req);
                        continue;
                }

                if (req->flags & REQ_F_BUFFER_SELECTED)
                        cflags = io_put_rw_kbuf(req);

                __io_cqring_fill_event(ctx, req->user_data, req->result, cflags);
                (*nr_events)++;

                if (req_ref_put_and_test(req))
                        io_req_free_batch(&rb, req, &ctx->submit_state);
        }

        io_commit_cqring(ctx);
        io_cqring_ev_posted_iopoll(ctx);
        io_req_free_batch_finish(ctx, &rb);
}

static int io_do_iopoll(struct io_ring_ctx *ctx, unsigned int *nr_events,
                        long min, bool resubmit)
{
        struct io_kiocb *req, *tmp;
        LIST_HEAD(done);
        bool spin;
        int ret;

        /*
         * Only spin for completions if we don't have multiple devices hanging
         * off our complete list, and we're under the requested amount.
         */
        spin = !ctx->poll_multi_queue && *nr_events < min;

        ret = 0;
        list_for_each_entry_safe(req, tmp, &ctx->iopoll_list, inflight_entry) {
                struct kiocb *kiocb = &req->rw.kiocb;

                /*
                 * Move completed and retryable entries to our local lists.
                 * If we find a request that requires polling, break out
                 * and complete those lists first, if we have entries there.
                 */
                if (READ_ONCE(req->iopoll_completed)) {
                        list_move_tail(&req->inflight_entry, &done);
                        continue;
                }
                if (!list_empty(&done))
                        break;

                ret = kiocb->ki_filp->f_op->iopoll(kiocb, spin);
                if (ret < 0)
                        break;

                /* iopoll may have completed current req */
                if (READ_ONCE(req->iopoll_completed))
                        list_move_tail(&req->inflight_entry, &done);

                if (ret && spin)
                        spin = false;
                ret = 0;
        }

        if (!list_empty(&done))
                io_iopoll_complete(ctx, nr_events, &done, resubmit);

        return ret;
}

/*
 * We can't just wait for polled events to come to us, we have to actively
 * find and complete them.
 */
static void io_iopoll_try_reap_events(struct io_ring_ctx *ctx)
{
        if (!(ctx->flags & IORING_SETUP_IOPOLL))
                return;

        mutex_lock(&ctx->uring_lock);
        while (!list_empty(&ctx->iopoll_list)) {
                unsigned int nr_events = 0;

                io_do_iopoll(ctx, &nr_events, 0, false);

                /* let it sleep and repeat later if can't complete a request */
                if (nr_events == 0)
                        break;
                /*
                 * Ensure we allow local-to-the-cpu processing to take place,
                 * in this case we need to ensure that we reap all events.
                 * Also let task_work, etc. to progress by releasing the mutex
                 */
                if (need_resched()) {
                        mutex_unlock(&ctx->uring_lock);
                        cond_resched();
                        mutex_lock(&ctx->uring_lock);
                }
        }
        mutex_unlock(&ctx->uring_lock);
}

static int io_iopoll_check(struct io_ring_ctx *ctx, long min)
{
        unsigned int nr_events = 0;
        int ret = 0;

        /*
         * We disallow the app entering submit/complete with polling, but we
         * still need to lock the ring to prevent racing with polled issue
         * that got punted to a workqueue.
         */
        mutex_lock(&ctx->uring_lock);
        /*
         * Don't enter poll loop if we already have events pending.
         * If we do, we can potentially be spinning for commands that
         * already triggered a CQE (eg in error).
         */
        if (test_bit(0, &ctx->check_cq_overflow))
                __io_cqring_overflow_flush(ctx, false);
        if (io_cqring_events(ctx))
                goto out;
        do {
                /*
                 * If a submit got punted to a workqueue, we can have the
                 * application entering polling for a command before it gets
                 * issued. That app will hold the uring_lock for the duration
                 * of the poll right here, so we need to take a breather every
                 * now and then to ensure that the issue has a chance to add
                 * the poll to the issued list. Otherwise we can spin here
                 * forever, while the workqueue is stuck trying to acquire the
                 * very same mutex.
                 */
                if (list_empty(&ctx->iopoll_list)) {
                        u32 tail = ctx->cached_cq_tail;

                        mutex_unlock(&ctx->uring_lock);
                        io_run_task_work();
                        mutex_lock(&ctx->uring_lock);

                        /* some requests don't go through iopoll_list */
                        if (tail != ctx->cached_cq_tail ||
                            list_empty(&ctx->iopoll_list))
                                break;
                }
                ret = io_do_iopoll(ctx, &nr_events, min, true);
        } while (!ret && nr_events < min && !need_resched());
out:
        mutex_unlock(&ctx->uring_lock);
        return ret;
}

static void kiocb_end_write(struct io_kiocb *req)
{
        /*
         * Tell lockdep we inherited freeze protection from submission
         * thread.
         */
        if (req->flags & REQ_F_ISREG) {
                struct super_block *sb = file_inode(req->file)->i_sb;

                __sb_writers_acquired(sb, SB_FREEZE_WRITE);
                sb_end_write(sb);
        }
}

#ifdef CONFIG_BLOCK
static bool io_resubmit_prep(struct io_kiocb *req)
{
        struct io_async_rw *rw = req->async_data;

        if (!rw)
                return !io_req_prep_async(req);
        /* may have left rw->iter inconsistent on -EIOCBQUEUED */
        iov_iter_revert(&rw->iter, req->result - iov_iter_count(&rw->iter));
        return true;
}

static bool io_rw_should_reissue(struct io_kiocb *req)
{
        umode_t mode = file_inode(req->file)->i_mode;
        struct io_ring_ctx *ctx = req->ctx;

        if (!S_ISBLK(mode) && !S_ISREG(mode))
                return false;
        if ((req->flags & REQ_F_NOWAIT) || (io_wq_current_is_worker() &&
            !(ctx->flags & IORING_SETUP_IOPOLL)))
                return false;
        /*
         * If ref is dying, we might be running poll reap from the exit work.
         * Don't attempt to reissue from that path, just let it fail with
         * -EAGAIN.
         */
        if (percpu_ref_is_dying(&ctx->refs))
                return false;
        /*
         * Play it safe and assume not safe to re-import and reissue if we're
         * not in the original thread group (or in task context).
         */
        if (!same_thread_group(req->task, current) || !in_task())
                return false;
        return true;
}
#else
static bool io_resubmit_prep(struct io_kiocb *req)
{
        return false;
}
static bool io_rw_should_reissue(struct io_kiocb *req)
{
        return false;
}
#endif

static void io_fallback_req_func(struct work_struct *work)
{
        struct io_ring_ctx *ctx = container_of(work, struct io_ring_ctx,
                                                fallback_work.work);
        struct llist_node *node = llist_del_all(&ctx->fallback_llist);
        struct io_kiocb *req, *tmp;

        percpu_ref_get(&ctx->refs);
        llist_for_each_entry_safe(req, tmp, node, io_task_work.fallback_node)
                req->io_task_work.func(req);
        percpu_ref_put(&ctx->refs);
}

static void __io_complete_rw(struct io_kiocb *req, long res, long res2,
                             unsigned int issue_flags)
{
        int cflags = 0;

        if (req->rw.kiocb.ki_flags & IOCB_WRITE)
                kiocb_end_write(req);
        if (res != req->result) {
                if ((res == -EAGAIN || res == -EOPNOTSUPP) &&
                    io_rw_should_reissue(req)) {
                        req->flags |= REQ_F_REISSUE;
                        return;
                }
                req_set_fail(req);
        }
        if (req->flags & REQ_F_BUFFER_SELECTED)
                cflags = io_put_rw_kbuf(req);
        __io_req_complete(req, issue_flags, res, cflags);
}

static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
{
        struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw.kiocb);

        __io_complete_rw(req, res, res2, 0);
}

static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2)
{
        struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw.kiocb);

        if (kiocb->ki_flags & IOCB_WRITE)
                kiocb_end_write(req);
        if (unlikely(res != req->result)) {
                if (!(res == -EAGAIN && io_rw_should_reissue(req) &&
                    io_resubmit_prep(req))) {
                        req_set_fail(req);
                        req->flags |= REQ_F_DONT_REISSUE;
                }
        }

        WRITE_ONCE(req->result, res);
        /* order with io_iopoll_complete() checking ->result */
        smp_wmb();
        WRITE_ONCE(req->iopoll_completed, 1);
}

/*
 * After the iocb has been issued, it's safe to be found on the poll list.
 * Adding the kiocb to the list AFTER submission ensures that we don't
 * find it from a io_do_iopoll() thread before the issuer is done
 * accessing the kiocb cookie.
 */
static void io_iopoll_req_issued(struct io_kiocb *req)
{
        struct io_ring_ctx *ctx = req->ctx;
        const bool in_async = io_wq_current_is_worker();

        /* workqueue context doesn't hold uring_lock, grab it now */
        if (unlikely(in_async))
                mutex_lock(&ctx->uring_lock);

        /*
         * Track whether we have multiple files in our lists. This will impact
         * how we do polling eventually, not spinning if we're on potentially
         * different devices.
         */
        if (list_empty(&ctx->iopoll_list)) {
                ctx->poll_multi_queue = false;
        } else if (!ctx->poll_multi_queue) {
                struct io_kiocb *list_req;
                unsigned int queue_num0, queue_num1;

                list_req = list_first_entry(&ctx->iopoll_list, struct io_kiocb,
                                                inflight_entry);

                if (list_req->file != req->file) {
                        ctx->poll_multi_queue = true;
                } else {
                        queue_num0 = blk_qc_t_to_queue_num(list_req->rw.kiocb.ki_cookie);
                        queue_num1 = blk_qc_t_to_queue_num(req->rw.kiocb.ki_cookie);
                        if (queue_num0 != queue_num1)
                                ctx->poll_multi_queue = true;
                }
        }

        /*
         * For fast devices, IO may have already completed. If it has, add
         * it to the front so we find it first.
         */
        if (READ_ONCE(req->iopoll_completed))
                list_add(&req->inflight_entry, &ctx->iopoll_list);
        else
                list_add_tail(&req->inflight_entry, &ctx->iopoll_list);

        if (unlikely(in_async)) {
                /*
                 * If IORING_SETUP_SQPOLL is enabled, sqes are either handle
                 * in sq thread task context or in io worker task context. If
                 * current task context is sq thread, we don't need to check
                 * whether should wake up sq thread.
                 */
                if ((ctx->flags & IORING_SETUP_SQPOLL) &&
                    wq_has_sleeper(&ctx->sq_data->wait))
                        wake_up(&ctx->sq_data->wait);

                mutex_unlock(&ctx->uring_lock);
        }
}

static inline void io_state_file_put(struct io_submit_state *state)
{
        if (state->file_refs) {
                fput_many(state->file, state->file_refs);
                state->file_refs = 0;
        }
}

/*
 * Get as many references to a file as we have IOs left in this submission,
 * assuming most submissions are for one file, or at least that each file
 * has more than one submission.
 */
static struct file *__io_file_get(struct io_submit_state *state, int fd)
{
        if (!state)
                return fget(fd);

        if (state->file_refs) {
                if (state->fd == fd) {
                        state->file_refs--;
                        return state->file;
                }
                io_state_file_put(state);
        }
        state->file = fget_many(fd, state->ios_left);
        if (unlikely(!state->file))
                return NULL;

        state->fd = fd;
        state->file_refs = state->ios_left - 1;
        return state->file;
}

static bool io_bdev_nowait(struct block_device *bdev)
{
        return !bdev || blk_queue_nowait(bdev_get_queue(bdev));
}

/*
 * If we tracked the file through the SCM inflight mechanism, we could support
 * any file. For now, just ensure that anything potentially problematic is done
 * inline.
 */
static bool __io_file_supports_async(struct file *file, int rw)
{
        umode_t mode = file_inode(file)->i_mode;

        if (S_ISBLK(mode)) {
                if (IS_ENABLED(CONFIG_BLOCK) &&
                    io_bdev_nowait(I_BDEV(file->f_mapping->host)))
                        return true;
                return false;
        }
        if (S_ISSOCK(mode))
                return true;
        if (S_ISREG(mode)) {
                if (IS_ENABLED(CONFIG_BLOCK) &&
                    io_bdev_nowait(file->f_inode->i_sb->s_bdev) &&
                    file->f_op != &io_uring_fops)
                        return true;
                return false;
        }

        /* any ->read/write should understand O_NONBLOCK */
        if (file->f_flags & O_NONBLOCK)
                return true;

        if (!(file->f_mode & FMODE_NOWAIT))
                return false;

        if (rw == READ)
                return file->f_op->read_iter != NULL;

        return file->f_op->write_iter != NULL;
}

static bool io_file_supports_async(struct io_kiocb *req, int rw)
{
        if (rw == READ && (req->flags & REQ_F_ASYNC_READ))
                return true;
        else if (rw == WRITE && (req->flags & REQ_F_ASYNC_WRITE))
                return true;

        return __io_file_supports_async(req->file, rw);
}

static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        struct io_ring_ctx *ctx = req->ctx;
        struct kiocb *kiocb = &req->rw.kiocb;
        struct file *file = req->file;
        unsigned ioprio;
        int ret;

        if (!(req->flags & REQ_F_ISREG) && S_ISREG(file_inode(file)->i_mode))
                req->flags |= REQ_F_ISREG;

        kiocb->ki_pos = READ_ONCE(sqe->off);
        if (kiocb->ki_pos == -1 && !(file->f_mode & FMODE_STREAM)) {
                req->flags |= REQ_F_CUR_POS;
                kiocb->ki_pos = file->f_pos;
        }
        kiocb->ki_hint = ki_hint_validate(file_write_hint(kiocb->ki_filp));
        kiocb->ki_flags = iocb_flags(kiocb->ki_filp);
        ret = kiocb_set_rw_flags(kiocb, READ_ONCE(sqe->rw_flags));
        if (unlikely(ret))
                return ret;

        /* don't allow async punt for O_NONBLOCK or RWF_NOWAIT */
        if ((kiocb->ki_flags & IOCB_NOWAIT) || (file->f_flags & O_NONBLOCK))
                req->flags |= REQ_F_NOWAIT;

        ioprio = READ_ONCE(sqe->ioprio);
        if (ioprio) {
                ret = ioprio_check_cap(ioprio);
                if (ret)
                        return ret;

                kiocb->ki_ioprio = ioprio;
        } else
                kiocb->ki_ioprio = get_current_ioprio();

        if (ctx->flags & IORING_SETUP_IOPOLL) {
                if (!(kiocb->ki_flags & IOCB_DIRECT) ||
                    !kiocb->ki_filp->f_op->iopoll)
                        return -EOPNOTSUPP;

                kiocb->ki_flags |= IOCB_HIPRI;
                kiocb->ki_complete = io_complete_rw_iopoll;
                req->iopoll_completed = 0;
        } else {
                if (kiocb->ki_flags & IOCB_HIPRI)
                        return -EINVAL;
                kiocb->ki_complete = io_complete_rw;
        }

        if (req->opcode == IORING_OP_READ_FIXED ||
            req->opcode == IORING_OP_WRITE_FIXED) {
                req->imu = NULL;
                io_req_set_rsrc_node(req);
        }

        req->rw.addr = READ_ONCE(sqe->addr);
        req->rw.len = READ_ONCE(sqe->len);
        req->buf_index = READ_ONCE(sqe->buf_index);
        return 0;
}

static inline void io_rw_done(struct kiocb *kiocb, ssize_t ret)
{
        switch (ret) {
        case -EIOCBQUEUED:
                break;
        case -ERESTARTSYS:
        case -ERESTARTNOINTR:
        case -ERESTARTNOHAND:
        case -ERESTART_RESTARTBLOCK:
                /*
                 * We can't just restart the syscall, since previously
                 * submitted sqes may already be in progress. Just fail this
                 * IO with EINTR.
                 */
                ret = -EINTR;
                fallthrough;
        default:
                kiocb->ki_complete(kiocb, ret, 0);
        }
}

static void kiocb_done(struct kiocb *kiocb, ssize_t ret,
                       unsigned int issue_flags)
{
        struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw.kiocb);
        struct io_async_rw *io = req->async_data;
        bool check_reissue = kiocb->ki_complete == io_complete_rw;

        /* add previously done IO, if any */
        if (io && io->bytes_done > 0) {
                if (ret < 0)
                        ret = io->bytes_done;
                else
                        ret += io->bytes_done;
        }

        if (req->flags & REQ_F_CUR_POS)
                req->file->f_pos = kiocb->ki_pos;
        if (ret >= 0 && check_reissue)
                __io_complete_rw(req, ret, 0, issue_flags);
        else
                io_rw_done(kiocb, ret);

        if (check_reissue && (req->flags & REQ_F_REISSUE)) {
                req->flags &= ~REQ_F_REISSUE;
                if (io_resubmit_prep(req)) {
                        req_ref_get(req);
                        io_req_task_queue_reissue(req);
                } else {
                        int cflags = 0;

                        req_set_fail(req);
                        if (req->flags & REQ_F_BUFFER_SELECTED)
                                cflags = io_put_rw_kbuf(req);
                        __io_req_complete(req, issue_flags, ret, cflags);
                }
        }
}

static int __io_import_fixed(struct io_kiocb *req, int rw, struct iov_iter *iter,
                             struct io_mapped_ubuf *imu)
{
        size_t len = req->rw.len;
        u64 buf_end, buf_addr = req->rw.addr;
        size_t offset;

        if (unlikely(check_add_overflow(buf_addr, (u64)len, &buf_end)))
                return -EFAULT;
        /* not inside the mapped region */
        if (unlikely(buf_addr < imu->ubuf || buf_end > imu->ubuf_end))
                return -EFAULT;

        /*
         * May not be a start of buffer, set size appropriately
         * and advance us to the beginning.
         */
        offset = buf_addr - imu->ubuf;
        iov_iter_bvec(iter, rw, imu->bvec, imu->nr_bvecs, offset + len);

        if (offset) {
                /*
                 * Don't use iov_iter_advance() here, as it's really slow for
                 * using the latter parts of a big fixed buffer - it iterates
                 * over each segment manually. We can cheat a bit here, because
                 * we know that:
                 *
                 * 1) it's a BVEC iter, we set it up
                 * 2) all bvecs are PAGE_SIZE in size, except potentially the
                 *    first and last bvec
                 *
                 * So just find our index, and adjust the iterator afterwards.
                 * If the offset is within the first bvec (or the whole first
                 * bvec, just use iov_iter_advance(). This makes it easier
                 * since we can just skip the first segment, which may not
                 * be PAGE_SIZE aligned.
                 */
                const struct bio_vec *bvec = imu->bvec;

                if (offset <= bvec->bv_len) {
                        iov_iter_advance(iter, offset);
                } else {
                        unsigned long seg_skip;

                        /* skip first vec */
                        offset -= bvec->bv_len;
                        seg_skip = 1 + (offset >> PAGE_SHIFT);

                        iter->bvec = bvec + seg_skip;
                        iter->nr_segs -= seg_skip;
                        iter->count -= bvec->bv_len + offset;
                        iter->iov_offset = offset & ~PAGE_MASK;
                }
        }

        return 0;
}

static int io_import_fixed(struct io_kiocb *req, int rw, struct iov_iter *iter)
{
        struct io_ring_ctx *ctx = req->ctx;
        struct io_mapped_ubuf *imu = req->imu;
        u16 index, buf_index = req->buf_index;

        if (likely(!imu)) {
                if (unlikely(buf_index >= ctx->nr_user_bufs))
                        return -EFAULT;
                index = array_index_nospec(buf_index, ctx->nr_user_bufs);
                imu = READ_ONCE(ctx->user_bufs[index]);
                req->imu = imu;
        }
        return __io_import_fixed(req, rw, iter, imu);
}

static void io_ring_submit_unlock(struct io_ring_ctx *ctx, bool needs_lock)
{
        if (needs_lock)
                mutex_unlock(&ctx->uring_lock);
}

static void io_ring_submit_lock(struct io_ring_ctx *ctx, bool needs_lock)
{
        /*
         * "Normal" inline submissions always hold the uring_lock, since we
         * grab it from the system call. Same is true for the SQPOLL offload.
         * The only exception is when we've detached the request and issue it
         * from an async worker thread, grab the lock for that case.
         */
        if (needs_lock)
                mutex_lock(&ctx->uring_lock);
}

static struct io_buffer *io_buffer_select(struct io_kiocb *req, size_t *len,
                                          int bgid, struct io_buffer *kbuf,
                                          bool needs_lock)
{
        struct io_buffer *head;

        if (req->flags & REQ_F_BUFFER_SELECTED)
                return kbuf;

        io_ring_submit_lock(req->ctx, needs_lock);

        lockdep_assert_held(&req->ctx->uring_lock);

        head = xa_load(&req->ctx->io_buffers, bgid);
        if (head) {
                if (!list_empty(&head->list)) {
                        kbuf = list_last_entry(&head->list, struct io_buffer,
                                                        list);
                        list_del(&kbuf->list);
                } else {
                        kbuf = head;
                        xa_erase(&req->ctx->io_buffers, bgid);
                }
                if (*len > kbuf->len)
                        *len = kbuf->len;
        } else {
                kbuf = ERR_PTR(-ENOBUFS);
        }

        io_ring_submit_unlock(req->ctx, needs_lock);

        return kbuf;
}

static void __user *io_rw_buffer_select(struct io_kiocb *req, size_t *len,
                                        bool needs_lock)
{
        struct io_buffer *kbuf;
        u16 bgid;

        kbuf = (struct io_buffer *) (unsigned long) req->rw.addr;
        bgid = req->buf_index;
        kbuf = io_buffer_select(req, len, bgid, kbuf, needs_lock);
        if (IS_ERR(kbuf))
                return kbuf;
        req->rw.addr = (u64) (unsigned long) kbuf;
        req->flags |= REQ_F_BUFFER_SELECTED;
        return u64_to_user_ptr(kbuf->addr);
}

#ifdef CONFIG_COMPAT
static ssize_t io_compat_import(struct io_kiocb *req, struct iovec *iov,
                                bool needs_lock)
{
        struct compat_iovec __user *uiov;
        compat_ssize_t clen;
        void __user *buf;
        ssize_t len;

        uiov = u64_to_user_ptr(req->rw.addr);
        if (!access_ok(uiov, sizeof(*uiov)))
                return -EFAULT;
        if (__get_user(clen, &uiov->iov_len))
                return -EFAULT;
        if (clen < 0)
                return -EINVAL;

        len = clen;
        buf = io_rw_buffer_select(req, &len, needs_lock);
        if (IS_ERR(buf))
                return PTR_ERR(buf);
        iov[0].iov_base = buf;
        iov[0].iov_len = (compat_size_t) len;
        return 0;
}
#endif

static ssize_t __io_iov_buffer_select(struct io_kiocb *req, struct iovec *iov,
                                      bool needs_lock)
{
        struct iovec __user *uiov = u64_to_user_ptr(req->rw.addr);
        void __user *buf;
        ssize_t len;

        if (copy_from_user(iov, uiov, sizeof(*uiov)))
                return -EFAULT;

        len = iov[0].iov_len;
        if (len < 0)
                return -EINVAL;
        buf = io_rw_buffer_select(req, &len, needs_lock);
        if (IS_ERR(buf))
                return PTR_ERR(buf);
        iov[0].iov_base = buf;
        iov[0].iov_len = len;
        return 0;
}

static ssize_t io_iov_buffer_select(struct io_kiocb *req, struct iovec *iov,
                                    bool needs_lock)
{
        if (req->flags & REQ_F_BUFFER_SELECTED) {
                struct io_buffer *kbuf;

                kbuf = (struct io_buffer *) (unsigned long) req->rw.addr;

                iov[0].iov_base = u64_to_user_ptr(kbuf->addr);
                iov[0].iov_len = kbuf->len;
                return 0;
        }
        if (req->rw.len != 1)
                return -EINVAL;

#ifdef CONFIG_COMPAT
        if (req->ctx->compat)
                return io_compat_import(req, iov, needs_lock);
#endif

        return __io_iov_buffer_select(req, iov, needs_lock);
}

static int io_import_iovec(int rw, struct io_kiocb *req, struct iovec **iovec,
                           struct iov_iter *iter, bool needs_lock)
{
        void __user *buf = u64_to_user_ptr(req->rw.addr);
        size_t sqe_len = req->rw.len;
        u8 opcode = req->opcode;
        ssize_t ret;

        if (opcode == IORING_OP_READ_FIXED || opcode == IORING_OP_WRITE_FIXED) {
                *iovec = NULL;
                return io_import_fixed(req, rw, iter);
        }

        /* buffer index only valid with fixed read/write, or buffer select  */
        if (req->buf_index && !(req->flags & REQ_F_BUFFER_SELECT))
                return -EINVAL;

        if (opcode == IORING_OP_READ || opcode == IORING_OP_WRITE) {
                if (req->flags & REQ_F_BUFFER_SELECT) {
                        buf = io_rw_buffer_select(req, &sqe_len, needs_lock);
                        if (IS_ERR(buf))
                                return PTR_ERR(buf);
                        req->rw.len = sqe_len;
                }

                ret = import_single_range(rw, buf, sqe_len, *iovec, iter);
                *iovec = NULL;
                return ret;
        }

        if (req->flags & REQ_F_BUFFER_SELECT) {
                ret = io_iov_buffer_select(req, *iovec, needs_lock);
                if (!ret)
                        iov_iter_init(iter, rw, *iovec, 1, (*iovec)->iov_len);
                *iovec = NULL;
                return ret;
        }

        return __import_iovec(rw, buf, sqe_len, UIO_FASTIOV, iovec, iter,
                              req->ctx->compat);
}

static inline loff_t *io_kiocb_ppos(struct kiocb *kiocb)
{
        return (kiocb->ki_filp->f_mode & FMODE_STREAM) ? NULL : &kiocb->ki_pos;
}

/*
 * For files that don't have ->read_iter() and ->write_iter(), handle them
 * by looping over ->read() or ->write() manually.
 */
static ssize_t loop_rw_iter(int rw, struct io_kiocb *req, struct iov_iter *iter)
{
        struct kiocb *kiocb = &req->rw.kiocb;
        struct file *file = req->file;
        ssize_t ret = 0;

        /*
         * Don't support polled IO through this interface, and we can't
         * support non-blocking either. For the latter, this just causes
         * the kiocb to be handled from an async context.
         */
        if (kiocb->ki_flags & IOCB_HIPRI)
                return -EOPNOTSUPP;
        if (kiocb->ki_flags & IOCB_NOWAIT)
                return -EAGAIN;

        while (iov_iter_count(iter)) {
                struct iovec iovec;
                ssize_t nr;

                if (!iov_iter_is_bvec(iter)) {
                        iovec = iov_iter_iovec(iter);
                } else {
                        iovec.iov_base = u64_to_user_ptr(req->rw.addr);
                        iovec.iov_len = req->rw.len;
                }

                if (rw == READ) {
                        nr = file->f_op->read(file, iovec.iov_base,
                                              iovec.iov_len, io_kiocb_ppos(kiocb));
                } else {
                        nr = file->f_op->write(file, iovec.iov_base,
                                               iovec.iov_len, io_kiocb_ppos(kiocb));
                }

                if (nr < 0) {
                        if (!ret)
                                ret = nr;
                        break;
                }
                ret += nr;
                if (nr != iovec.iov_len)
                        break;
                req->rw.len -= nr;
                req->rw.addr += nr;
                iov_iter_advance(iter, nr);
        }

        return ret;
}

static void io_req_map_rw(struct io_kiocb *req, const struct iovec *iovec,
                          const struct iovec *fast_iov, struct iov_iter *iter)
{
        struct io_async_rw *rw = req->async_data;

        memcpy(&rw->iter, iter, sizeof(*iter));
        rw->free_iovec = iovec;
        rw->bytes_done = 0;
        /* can only be fixed buffers, no need to do anything */
        if (iov_iter_is_bvec(iter))
                return;
        if (!iovec) {
                unsigned iov_off = 0;

                rw->iter.iov = rw->fast_iov;
                if (iter->iov != fast_iov) {
                        iov_off = iter->iov - fast_iov;
                        rw->iter.iov += iov_off;
                }
                if (rw->fast_iov != fast_iov)
                        memcpy(rw->fast_iov + iov_off, fast_iov + iov_off,
                               sizeof(struct iovec) * iter->nr_segs);
        } else {
                req->flags |= REQ_F_NEED_CLEANUP;
        }
}

static inline int io_alloc_async_data(struct io_kiocb *req)
{
        WARN_ON_ONCE(!io_op_defs[req->opcode].async_size);
        req->async_data = kmalloc(io_op_defs[req->opcode].async_size, GFP_KERNEL);
        return req->async_data == NULL;
}

static int io_setup_async_rw(struct io_kiocb *req, const struct iovec *iovec,
                             const struct iovec *fast_iov,
                             struct iov_iter *iter, bool force)
{
        if (!force && !io_op_defs[req->opcode].needs_async_setup)
                return 0;
        if (!req->async_data) {
                if (io_alloc_async_data(req)) {
                        kfree(iovec);
                        return -ENOMEM;
                }

                io_req_map_rw(req, iovec, fast_iov, iter);
        }
        return 0;
}

static inline int io_rw_prep_async(struct io_kiocb *req, int rw)
{
        struct io_async_rw *iorw = req->async_data;
        struct iovec *iov = iorw->fast_iov;
        int ret;

        ret = io_import_iovec(rw, req, &iov, &iorw->iter, false);
        if (unlikely(ret < 0))
                return ret;

        iorw->bytes_done = 0;
        iorw->free_iovec = iov;
        if (iov)
                req->flags |= REQ_F_NEED_CLEANUP;
        return 0;
}

static int io_read_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        if (unlikely(!(req->file->f_mode & FMODE_READ)))
                return -EBADF;
        return io_prep_rw(req, sqe);
}

/*
 * This is our waitqueue callback handler, registered through lock_page_async()
 * when we initially tried to do the IO with the iocb armed our waitqueue.
 * This gets called when the page is unlocked, and we generally expect that to
 * happen when the page IO is completed and the page is now uptodate. This will
 * queue a task_work based retry of the operation, attempting to copy the data
 * again. If the latter fails because the page was NOT uptodate, then we will
 * do a thread based blocking retry of the operation. That's the unexpected
 * slow path.
 */
static int io_async_buf_func(struct wait_queue_entry *wait, unsigned mode,
                             int sync, void *arg)
{
        struct wait_page_queue *wpq;
        struct io_kiocb *req = wait->private;
        struct wait_page_key *key = arg;

        wpq = container_of(wait, struct wait_page_queue, wait);

        if (!wake_page_match(wpq, key))
                return 0;

        req->rw.kiocb.ki_flags &= ~IOCB_WAITQ;
        list_del_init(&wait->entry);

        /* submit ref gets dropped, acquire a new one */
        req_ref_get(req);
        io_req_task_queue(req);
        return 1;
}

/*
 * This controls whether a given IO request should be armed for async page
 * based retry. If we return false here, the request is handed to the async
 * worker threads for retry. If we're doing buffered reads on a regular file,
 * we prepare a private wait_page_queue entry and retry the operation. This
 * will either succeed because the page is now uptodate and unlocked, or it
 * will register a callback when the page is unlocked at IO completion. Through
 * that callback, io_uring uses task_work to setup a retry of the operation.
 * That retry will attempt the buffered read again. The retry will generally
 * succeed, or in rare cases where it fails, we then fall back to using the
 * async worker threads for a blocking retry.
 */
static bool io_rw_should_retry(struct io_kiocb *req)
{
        struct io_async_rw *rw = req->async_data;
        struct wait_page_queue *wait = &rw->wpq;
        struct kiocb *kiocb = &req->rw.kiocb;

        /* never retry for NOWAIT, we just complete with -EAGAIN */
        if (req->flags & REQ_F_NOWAIT)
                return false;

        /* Only for buffered IO */
        if (kiocb->ki_flags & (IOCB_DIRECT | IOCB_HIPRI))
                return false;

        /*
         * just use poll if we can, and don't attempt if the fs doesn't
         * support callback based unlocks
         */
        if (file_can_poll(req->file) || !(req->file->f_mode & FMODE_BUF_RASYNC))
                return false;

        wait->wait.func = io_async_buf_func;
        wait->wait.private = req;
        wait->wait.flags = 0;
        INIT_LIST_HEAD(&wait->wait.entry);
        kiocb->ki_flags |= IOCB_WAITQ;
        kiocb->ki_flags &= ~IOCB_NOWAIT;
        kiocb->ki_waitq = wait;
        return true;
}

static inline int io_iter_do_read(struct io_kiocb *req, struct iov_iter *iter)
{
        if (req->file->f_op->read_iter)
                return call_read_iter(req->file, &req->rw.kiocb, iter);
        else if (req->file->f_op->read)
                return loop_rw_iter(READ, req, iter);
        else
                return -EINVAL;
}

static int io_read(struct io_kiocb *req, unsigned int issue_flags)
{
        struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
        struct kiocb *kiocb = &req->rw.kiocb;
        struct iov_iter __iter, *iter = &__iter;
        struct io_async_rw *rw = req->async_data;
        ssize_t io_size, ret, ret2;
        bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;

        if (rw) {
                iter = &rw->iter;
                iovec = NULL;
        } else {
                ret = io_import_iovec(READ, req, &iovec, iter, !force_nonblock);
                if (ret < 0)
                        return ret;
        }
        io_size = iov_iter_count(iter);
        req->result = io_size;

        /* Ensure we clear previously set non-block flag */
        if (!force_nonblock)
                kiocb->ki_flags &= ~IOCB_NOWAIT;
        else
                kiocb->ki_flags |= IOCB_NOWAIT;

        /* If the file doesn't support async, just async punt */
        if (force_nonblock && !io_file_supports_async(req, READ)) {
                ret = io_setup_async_rw(req, iovec, inline_vecs, iter, true);
                return ret ?: -EAGAIN;
        }

        ret = rw_verify_area(READ, req->file, io_kiocb_ppos(kiocb), io_size);
        if (unlikely(ret)) {
                kfree(iovec);
                return ret;
        }

        ret = io_iter_do_read(req, iter);

        if (ret == -EAGAIN || (req->flags & REQ_F_REISSUE)) {
                req->flags &= ~REQ_F_REISSUE;
                /* IOPOLL retry should happen for io-wq threads */
                if (!force_nonblock && !(req->ctx->flags & IORING_SETUP_IOPOLL))
                        goto done;
                /* no retry on NONBLOCK nor RWF_NOWAIT */
                if (req->flags & REQ_F_NOWAIT)
                        goto done;
                /* some cases will consume bytes even on error returns */
                iov_iter_revert(iter, io_size - iov_iter_count(iter));
                ret = 0;
        } else if (ret == -EIOCBQUEUED) {
                goto out_free;
        } else if (ret <= 0 || ret == io_size || !force_nonblock ||
                   (req->flags & REQ_F_NOWAIT) || !(req->flags & REQ_F_ISREG)) {
                /* read all, failed, already did sync or don't want to retry */
                goto done;
        }

        ret2 = io_setup_async_rw(req, iovec, inline_vecs, iter, true);
        if (ret2)
                return ret2;

        iovec = NULL;
        rw = req->async_data;
        /* now use our persistent iterator, if we aren't already */
        iter = &rw->iter;

        do {
                io_size -= ret;
                rw->bytes_done += ret;
                /* if we can retry, do so with the callbacks armed */
                if (!io_rw_should_retry(req)) {
                        kiocb->ki_flags &= ~IOCB_WAITQ;
                        return -EAGAIN;
                }

                /*
                 * Now retry read with the IOCB_WAITQ parts set in the iocb. If
                 * we get -EIOCBQUEUED, then we'll get a notification when the
                 * desired page gets unlocked. We can also get a partial read
                 * here, and if we do, then just retry at the new offset.
                 */
                ret = io_iter_do_read(req, iter);
                if (ret == -EIOCBQUEUED)
                        return 0;
                /* we got some bytes, but not all. retry. */
                kiocb->ki_flags &= ~IOCB_WAITQ;
        } while (ret > 0 && ret < io_size);
done:
        kiocb_done(kiocb, ret, issue_flags);
out_free:
        /* it's faster to check here then delegate to kfree */
        if (iovec)
                kfree(iovec);
        return 0;
}

static int io_write_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        if (unlikely(!(req->file->f_mode & FMODE_WRITE)))
                return -EBADF;
        return io_prep_rw(req, sqe);
}

static int io_write(struct io_kiocb *req, unsigned int issue_flags)
{
        struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
        struct kiocb *kiocb = &req->rw.kiocb;
        struct iov_iter __iter, *iter = &__iter;
        struct io_async_rw *rw = req->async_data;
        ssize_t ret, ret2, io_size;
        bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;

        if (rw) {
                iter = &rw->iter;
                iovec = NULL;
        } else {
                ret = io_import_iovec(WRITE, req, &iovec, iter, !force_nonblock);
                if (ret < 0)
                        return ret;
        }
        io_size = iov_iter_count(iter);
        req->result = io_size;

        /* Ensure we clear previously set non-block flag */
        if (!force_nonblock)
                kiocb->ki_flags &= ~IOCB_NOWAIT;
        else
                kiocb->ki_flags |= IOCB_NOWAIT;

        /* If the file doesn't support async, just async punt */
        if (force_nonblock && !io_file_supports_async(req, WRITE))
                goto copy_iov;

        /* file path doesn't support NOWAIT for non-direct_IO */
        if (force_nonblock && !(kiocb->ki_flags & IOCB_DIRECT) &&
            (req->flags & REQ_F_ISREG))
                goto copy_iov;

        ret = rw_verify_area(WRITE, req->file, io_kiocb_ppos(kiocb), io_size);
        if (unlikely(ret))
                goto out_free;

        /*
         * Open-code file_start_write here to grab freeze protection,
         * which will be released by another thread in
         * io_complete_rw().  Fool lockdep by telling it the lock got
         * released so that it doesn't complain about the held lock when
         * we return to userspace.
         */
        if (req->flags & REQ_F_ISREG) {
                sb_start_write(file_inode(req->file)->i_sb);
                __sb_writers_release(file_inode(req->file)->i_sb,
                                        SB_FREEZE_WRITE);
        }
        kiocb->ki_flags |= IOCB_WRITE;

        if (req->file->f_op->write_iter)
                ret2 = call_write_iter(req->file, kiocb, iter);
        else if (req->file->f_op->write)
                ret2 = loop_rw_iter(WRITE, req, iter);
        else
                ret2 = -EINVAL;

        if (req->flags & REQ_F_REISSUE) {
                req->flags &= ~REQ_F_REISSUE;
                ret2 = -EAGAIN;
        }

        /*
         * Raw bdev writes will return -EOPNOTSUPP for IOCB_NOWAIT. Just
         * retry them without IOCB_NOWAIT.
         */
        if (ret2 == -EOPNOTSUPP && (kiocb->ki_flags & IOCB_NOWAIT))
                ret2 = -EAGAIN;
        /* no retry on NONBLOCK nor RWF_NOWAIT */
        if (ret2 == -EAGAIN && (req->flags & REQ_F_NOWAIT))
                goto done;
        if (!force_nonblock || ret2 != -EAGAIN) {
                /* IOPOLL retry should happen for io-wq threads */
                if ((req->ctx->flags & IORING_SETUP_IOPOLL) && ret2 == -EAGAIN)
                        goto copy_iov;
done:
                kiocb_done(kiocb, ret2, issue_flags);
        } else {
copy_iov:
                /* some cases will consume bytes even on error returns */
                iov_iter_revert(iter, io_size - iov_iter_count(iter));
                ret = io_setup_async_rw(req, iovec, inline_vecs, iter, false);
                return ret ?: -EAGAIN;
        }
out_free:
        /* it's reportedly faster than delegating the null check to kfree() */
        if (iovec)
                kfree(iovec);
        return ret;
}

static int io_renameat_prep(struct io_kiocb *req,
                            const struct io_uring_sqe *sqe)
{
        struct io_rename *ren = &req->rename;
        const char __user *oldf, *newf;

        if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
                return -EINVAL;
        if (sqe->ioprio || sqe->buf_index)
                return -EINVAL;
        if (unlikely(req->flags & REQ_F_FIXED_FILE))
                return -EBADF;

        ren->old_dfd = READ_ONCE(sqe->fd);
        oldf = u64_to_user_ptr(READ_ONCE(sqe->addr));
        newf = u64_to_user_ptr(READ_ONCE(sqe->addr2));
        ren->new_dfd = READ_ONCE(sqe->len);
        ren->flags = READ_ONCE(sqe->rename_flags);

        ren->oldpath = getname(oldf);
        if (IS_ERR(ren->oldpath))
                return PTR_ERR(ren->oldpath);

        ren->newpath = getname(newf);
        if (IS_ERR(ren->newpath)) {
                putname(ren->oldpath);
                return PTR_ERR(ren->newpath);
        }

        req->flags |= REQ_F_NEED_CLEANUP;
        return 0;
}

static int io_renameat(struct io_kiocb *req, unsigned int issue_flags)
{
        struct io_rename *ren = &req->rename;
        int ret;

        if (issue_flags & IO_URING_F_NONBLOCK)
                return -EAGAIN;

        ret = do_renameat2(ren->old_dfd, ren->oldpath, ren->new_dfd,
                                ren->newpath, ren->flags);

        req->flags &= ~REQ_F_NEED_CLEANUP;
        if (ret < 0)
                req_set_fail(req);
        io_req_complete(req, ret);
        return 0;
}

static int io_unlinkat_prep(struct io_kiocb *req,
                            const struct io_uring_sqe *sqe)
{
        struct io_unlink *un = &req->unlink;
        const char __user *fname;

        if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
                return -EINVAL;
        if (sqe->ioprio || sqe->off || sqe->len || sqe->buf_index)
                return -EINVAL;
        if (unlikely(req->flags & REQ_F_FIXED_FILE))
                return -EBADF;

        un->dfd = READ_ONCE(sqe->fd);

        un->flags = READ_ONCE(sqe->unlink_flags);
        if (un->flags & ~AT_REMOVEDIR)
                return -EINVAL;

        fname = u64_to_user_ptr(READ_ONCE(sqe->addr));
        un->filename = getname(fname);
        if (IS_ERR(un->filename))
                return PTR_ERR(un->filename);

        req->flags |= REQ_F_NEED_CLEANUP;
        return 0;
}

static int io_unlinkat(struct io_kiocb *req, unsigned int issue_flags)
{
        struct io_unlink *un = &req->unlink;
        int ret;

        if (issue_flags & IO_URING_F_NONBLOCK)
                return -EAGAIN;

        if (un->flags & AT_REMOVEDIR)
                ret = do_rmdir(un->dfd, un->filename);
        else
                ret = do_unlinkat(un->dfd, un->filename);

        req->flags &= ~REQ_F_NEED_CLEANUP;
        if (ret < 0)
                req_set_fail(req);
        io_req_complete(req, ret);
        return 0;
}

static int io_shutdown_prep(struct io_kiocb *req,
                            const struct io_uring_sqe *sqe)
{
#if defined(CONFIG_NET)
        if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
                return -EINVAL;
        if (sqe->ioprio || sqe->off || sqe->addr || sqe->rw_flags ||
            sqe->buf_index)
                return -EINVAL;

        req->shutdown.how = READ_ONCE(sqe->len);
        return 0;
#else
        return -EOPNOTSUPP;
#endif
}

static int io_shutdown(struct io_kiocb *req, unsigned int issue_flags)
{
#if defined(CONFIG_NET)
        struct socket *sock;
        int ret;

        if (issue_flags & IO_URING_F_NONBLOCK)
                return -EAGAIN;

        sock = sock_from_file(req->file);
        if (unlikely(!sock))
                return -ENOTSOCK;

        ret = __sys_shutdown_sock(sock, req->shutdown.how);
        if (ret < 0)
                req_set_fail(req);
        io_req_complete(req, ret);
        return 0;
#else
        return -EOPNOTSUPP;
#endif
}

static int __io_splice_prep(struct io_kiocb *req,
                            const struct io_uring_sqe *sqe)
{
        struct io_splice *sp = &req->splice;
        unsigned int valid_flags = SPLICE_F_FD_IN_FIXED | SPLICE_F_ALL;

        if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
                return -EINVAL;

        sp->file_in = NULL;
        sp->len = READ_ONCE(sqe->len);
        sp->flags = READ_ONCE(sqe->splice_flags);

        if (unlikely(sp->flags & ~valid_flags))
                return -EINVAL;

        sp->file_in = io_file_get(NULL, req, READ_ONCE(sqe->splice_fd_in),
                                  (sp->flags & SPLICE_F_FD_IN_FIXED));
        if (!sp->file_in)
                return -EBADF;
        req->flags |= REQ_F_NEED_CLEANUP;
        return 0;
}

static int io_tee_prep(struct io_kiocb *req,
                       const struct io_uring_sqe *sqe)
{
        if (READ_ONCE(sqe->splice_off_in) || READ_ONCE(sqe->off))
                return -EINVAL;
        return __io_splice_prep(req, sqe);
}

static int io_tee(struct io_kiocb *req, unsigned int issue_flags)
{
        struct io_splice *sp = &req->splice;
        struct file *in = sp->file_in;
        struct file *out = sp->file_out;
        unsigned int flags = sp->flags & ~SPLICE_F_FD_IN_FIXED;
        long ret = 0;

        if (issue_flags & IO_URING_F_NONBLOCK)
                return -EAGAIN;
        if (sp->len)
                ret = do_tee(in, out, sp->len, flags);

        if (!(sp->flags & SPLICE_F_FD_IN_FIXED))
                io_put_file(in);
        req->flags &= ~REQ_F_NEED_CLEANUP;

        if (ret != sp->len)
                req_set_fail(req);
        io_req_complete(req, ret);
        return 0;
}

static int io_splice_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        struct io_splice *sp = &req->splice;

        sp->off_in = READ_ONCE(sqe->splice_off_in);
        sp->off_out = READ_ONCE(sqe->off);
        return __io_splice_prep(req, sqe);
}

static int io_splice(struct io_kiocb *req, unsigned int issue_flags)
{
        struct io_splice *sp = &req->splice;
        struct file *in = sp->file_in;
        struct file *out = sp->file_out;
        unsigned int flags = sp->flags & ~SPLICE_F_FD_IN_FIXED;
        loff_t *poff_in, *poff_out;
        long ret = 0;

        if (issue_flags & IO_URING_F_NONBLOCK)
                return -EAGAIN;

        poff_in = (sp->off_in == -1) ? NULL : &sp->off_in;
        poff_out = (sp->off_out == -1) ? NULL : &sp->off_out;

        if (sp->len)
                ret = do_splice(in, poff_in, out, poff_out, sp->len, flags);

        if (!(sp->flags & SPLICE_F_FD_IN_FIXED))
                io_put_file(in);
        req->flags &= ~REQ_F_NEED_CLEANUP;

        if (ret != sp->len)
                req_set_fail(req);
        io_req_complete(req, ret);
        return 0;
}

/*
 * IORING_OP_NOP just posts a completion event, nothing else.
 */
static int io_nop(struct io_kiocb *req, unsigned int issue_flags)
{
        struct io_ring_ctx *ctx = req->ctx;

        if (unlikely(ctx->flags & IORING_SETUP_IOPOLL))
                return -EINVAL;

        __io_req_complete(req, issue_flags, 0, 0);
        return 0;
}

static int io_fsync_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        struct io_ring_ctx *ctx = req->ctx;

        if (!req->file)
                return -EBADF;

        if (unlikely(ctx->flags & IORING_SETUP_IOPOLL))
                return -EINVAL;
        if (unlikely(sqe->addr || sqe->ioprio || sqe->buf_index))
                return -EINVAL;

        req->sync.flags = READ_ONCE(sqe->fsync_flags);
        if (unlikely(req->sync.flags & ~IORING_FSYNC_DATASYNC))
                return -EINVAL;

        req->sync.off = READ_ONCE(sqe->off);
        req->sync.len = READ_ONCE(sqe->len);
        return 0;
}

static int io_fsync(struct io_kiocb *req, unsigned int issue_flags)
{
        loff_t end = req->sync.off + req->sync.len;
        int ret;

        /* fsync always requires a blocking context */
        if (issue_flags & IO_URING_F_NONBLOCK)
                return -EAGAIN;

        ret = vfs_fsync_range(req->file, req->sync.off,
                                end > 0 ? end : LLONG_MAX,
                                req->sync.flags & IORING_FSYNC_DATASYNC);
        if (ret < 0)
                req_set_fail(req);
        io_req_complete(req, ret);
        return 0;
}

static int io_fallocate_prep(struct io_kiocb *req,
                             const struct io_uring_sqe *sqe)
{
        if (sqe->ioprio || sqe->buf_index || sqe->rw_flags)
                return -EINVAL;
        if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
                return -EINVAL;

        req->sync.off = READ_ONCE(sqe->off);
        req->sync.len = READ_ONCE(sqe->addr);
        req->sync.mode = READ_ONCE(sqe->len);
        return 0;
}

static int io_fallocate(struct io_kiocb *req, unsigned int issue_flags)
{
        int ret;

        /* fallocate always requiring blocking context */
        if (issue_flags & IO_URING_F_NONBLOCK)
                return -EAGAIN;
        ret = vfs_fallocate(req->file, req->sync.mode, req->sync.off,
                                req->sync.len);
        if (ret < 0)
                req_set_fail(req);
        io_req_complete(req, ret);
        return 0;
}

static int __io_openat_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        const char __user *fname;
        int ret;

        if (unlikely(sqe->ioprio || sqe->buf_index))
                return -EINVAL;
        if (unlikely(req->flags & REQ_F_FIXED_FILE))
                return -EBADF;

        /* open.how should be already initialised */
        if (!(req->open.how.flags & O_PATH) && force_o_largefile())
                req->open.how.flags |= O_LARGEFILE;

        req->open.dfd = READ_ONCE(sqe->fd);
        fname = u64_to_user_ptr(READ_ONCE(sqe->addr));
        req->open.filename = getname(fname);
        if (IS_ERR(req->open.filename)) {
                ret = PTR_ERR(req->open.filename);
                req->open.filename = NULL;
                return ret;
        }
        req->open.nofile = rlimit(RLIMIT_NOFILE);
        req->flags |= REQ_F_NEED_CLEANUP;
        return 0;
}

static int io_openat_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        u64 flags, mode;

        if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
                return -EINVAL;
        mode = READ_ONCE(sqe->len);
        flags = READ_ONCE(sqe->open_flags);
        req->open.how = build_open_how(flags, mode);
        return __io_openat_prep(req, sqe);
}

static int io_openat2_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        struct open_how __user *how;
        size_t len;
        int ret;

        if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
                return -EINVAL;
        how = u64_to_user_ptr(READ_ONCE(sqe->addr2));
        len = READ_ONCE(sqe->len);
        if (len < OPEN_HOW_SIZE_VER0)
                return -EINVAL;

        ret = copy_struct_from_user(&req->open.how, sizeof(req->open.how), how,
                                        len);
        if (ret)
                return ret;

        return __io_openat_prep(req, sqe);
}

static int io_openat2(struct io_kiocb *req, unsigned int issue_flags)
{
        struct open_flags op;
        struct file *file;
        bool nonblock_set;
        bool resolve_nonblock;
        int ret;

        ret = build_open_flags(&req->open.how, &op);
        if (ret)
                goto err;
        nonblock_set = op.open_flag & O_NONBLOCK;
        resolve_nonblock = req->open.how.resolve & RESOLVE_CACHED;
        if (issue_flags & IO_URING_F_NONBLOCK) {
                /*
                 * Don't bother trying for O_TRUNC, O_CREAT, or O_TMPFILE open,
                 * it'll always -EAGAIN
                 */
                if (req->open.how.flags & (O_TRUNC | O_CREAT | O_TMPFILE))
                        return -EAGAIN;
                op.lookup_flags |= LOOKUP_CACHED;
                op.open_flag |= O_NONBLOCK;
        }

        ret = __get_unused_fd_flags(req->open.how.flags, req->open.nofile);
        if (ret < 0)
                goto err;

        file = do_filp_open(req->open.dfd, req->open.filename, &op);
        if (IS_ERR(file)) {
                /*
                 * We could hang on to this 'fd' on retrying, but seems like
                 * marginal gain for something that is now known to be a slower
                 * path. So just put it, and we'll get a new one when we retry.
                 */
                put_unused_fd(ret);

                ret = PTR_ERR(file);
                /* only retry if RESOLVE_CACHED wasn't already set by application */
                if (ret == -EAGAIN &&
                    (!resolve_nonblock && (issue_flags & IO_URING_F_NONBLOCK)))
                        return -EAGAIN;
                goto err;
        }

        if ((issue_flags & IO_URING_F_NONBLOCK) && !nonblock_set)
                file->f_flags &= ~O_NONBLOCK;
        fsnotify_open(file);
        fd_install(ret, file);
err:
        putname(req->open.filename);
        req->flags &= ~REQ_F_NEED_CLEANUP;
        if (ret < 0)
                req_set_fail(req);
        __io_req_complete(req, issue_flags, ret, 0);
        return 0;
}

static int io_openat(struct io_kiocb *req, unsigned int issue_flags)
{
        return io_openat2(req, issue_flags);
}

static int io_remove_buffers_prep(struct io_kiocb *req,
                                  const struct io_uring_sqe *sqe)
{
        struct io_provide_buf *p = &req->pbuf;
        u64 tmp;

        if (sqe->ioprio || sqe->rw_flags || sqe->addr || sqe->len || sqe->off)
                return -EINVAL;

        tmp = READ_ONCE(sqe->fd);
        if (!tmp || tmp > USHRT_MAX)
                return -EINVAL;

        memset(p, 0, sizeof(*p));
        p->nbufs = tmp;
        p->bgid = READ_ONCE(sqe->buf_group);
        return 0;
}

static int __io_remove_buffers(struct io_ring_ctx *ctx, struct io_buffer *buf,
                               int bgid, unsigned nbufs)
{
        unsigned i = 0;

        /* shouldn't happen */
        if (!nbufs)
                return 0;

        /* the head kbuf is the list itself */
        while (!list_empty(&buf->list)) {
                struct io_buffer *nxt;

                nxt = list_first_entry(&buf->list, struct io_buffer, list);
                list_del(&nxt->list);
                kfree(nxt);
                if (++i == nbufs)
                        return i;
        }
        i++;
        kfree(buf);
        xa_erase(&ctx->io_buffers, bgid);

        return i;
}

static int io_remove_buffers(struct io_kiocb *req, unsigned int issue_flags)
{
        struct io_provide_buf *p = &req->pbuf;
        struct io_ring_ctx *ctx = req->ctx;
        struct io_buffer *head;
        int ret = 0;
        bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;

        io_ring_submit_lock(ctx, !force_nonblock);

        lockdep_assert_held(&ctx->uring_lock);

        ret = -ENOENT;
        head = xa_load(&ctx->io_buffers, p->bgid);
        if (head)
                ret = __io_remove_buffers(ctx, head, p->bgid, p->nbufs);
        if (ret < 0)
                req_set_fail(req);

        /* complete before unlock, IOPOLL may need the lock */
        __io_req_complete(req, issue_flags, ret, 0);
        io_ring_submit_unlock(ctx, !force_nonblock);
        return 0;
}

static int io_provide_buffers_prep(struct io_kiocb *req,
                                   const struct io_uring_sqe *sqe)
{
        unsigned long size, tmp_check;
        struct io_provide_buf *p = &req->pbuf;
        u64 tmp;

        if (sqe->ioprio || sqe->rw_flags)
                return -EINVAL;

        tmp = READ_ONCE(sqe->fd);
        if (!tmp || tmp > USHRT_MAX)
                return -E2BIG;
        p->nbufs = tmp;
        p->addr = READ_ONCE(sqe->addr);
        p->len = READ_ONCE(sqe->len);

        if (check_mul_overflow((unsigned long)p->len, (unsigned long)p->nbufs,
                                &size))