/*
 * Resizable virtual memory filesystem for Linux.
 *
 * Copyright (C) 2000 Linus Torvalds.
 *               2000 Transmeta Corp.
 *               2000-2001 Christoph Rohland
 *               2000-2001 SAP AG
 *               2002 Red Hat Inc.
 * Copyright (C) 2002-2011 Hugh Dickins.
 * Copyright (C) 2011 Google Inc.
 * Copyright (C) 2002-2005 VERITAS Software Corporation.
 * Copyright (C) 2004 Andi Kleen, SuSE Labs
 *
 * Extended attribute support for tmpfs:
 * Copyright (c) 2004, Luke Kenneth Casson Leighton <lkcl@lkcl.net>
 * Copyright (c) 2004 Red Hat, Inc., James Morris <jmorris@redhat.com>
 *
 * tiny-shmem:
 * Copyright (c) 2004, 2008 Matt Mackall <mpm@selenic.com>
 *
 * This file is released under the GPL.
 */

#include <linux/fs.h>
#include <linux/init.h>
#include <linux/vfs.h>
#include <linux/mount.h>
#include <linux/ramfs.h>
#include <linux/pagemap.h>
#include <linux/file.h>
#include <linux/mm.h>
#include <linux/random.h>
#include <linux/sched/signal.h>
#include <linux/export.h>
#include <linux/swap.h>
#include <linux/uio.h>
#include <linux/khugepaged.h>
#include <linux/hugetlb.h>
#include <linux/frontswap.h>

#include <asm/tlbflush.h> /* for arch/microblaze update_mmu_cache() */

static struct vfsmount *shm_mnt;

#ifdef CONFIG_SHMEM
/*
 * This virtual memory filesystem is heavily based on the ramfs. It
 * extends ramfs by the ability to use swap and honor resource limits
 * which makes it a completely usable filesystem.
 */

#include <linux/xattr.h>
#include <linux/exportfs.h>
#include <linux/posix_acl.h>
#include <linux/posix_acl_xattr.h>
#include <linux/mman.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/backing-dev.h>
#include <linux/shmem_fs.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/pagevec.h>
#include <linux/percpu_counter.h>
#include <linux/falloc.h>
#include <linux/splice.h>
#include <linux/security.h>
#include <linux/swapops.h>
#include <linux/mempolicy.h>
#include <linux/namei.h>
#include <linux/ctype.h>
#include <linux/migrate.h>
#include <linux/highmem.h>
#include <linux/seq_file.h>
#include <linux/magic.h>
#include <linux/syscalls.h>
#include <linux/fcntl.h>
#include <uapi/linux/memfd.h>
#include <linux/userfaultfd_k.h>
#include <linux/rmap.h>
#include <linux/uuid.h>

#include <linux/uaccess.h>
#include <asm/pgtable.h>

#include "internal.h"

#define BLOCKS_PER_PAGE  (PAGE_SIZE/512)
#define VM_ACCT(size)    (PAGE_ALIGN(size) >> PAGE_SHIFT)

/* Pretend that each entry is of this size in directory's i_size */
#define BOGO_DIRENT_SIZE 20

/* Symlink up to this size is kmalloc'ed instead of using a swappable page */
#define SHORT_SYMLINK_LEN 128

/*
 * shmem_fallocate communicates with shmem_fault or shmem_writepage via
 * inode->i_private (with i_mutex making sure that it has only one user at
 * a time): we would prefer not to enlarge the shmem inode just for that.
 */
struct shmem_falloc {
        wait_queue_head_t *waitq; /* faults into hole wait for punch to end */
        pgoff_t start;          /* start of range currently being fallocated */
        pgoff_t next;           /* the next page offset to be fallocated */
        pgoff_t nr_falloced;    /* how many new pages have been fallocated */
        pgoff_t nr_unswapped;   /* how often writepage refused to swap out */
};

#ifdef CONFIG_TMPFS
static unsigned long shmem_default_max_blocks(void)
{
        return totalram_pages() / 2;
}

static unsigned long shmem_default_max_inodes(void)
{
        unsigned long nr_pages = totalram_pages();

        return min(nr_pages - totalhigh_pages(), nr_pages / 2);
}
#endif

static bool shmem_should_replace_page(struct page *page, gfp_t gfp);
static int shmem_replace_page(struct page **pagep, gfp_t gfp,
                                struct shmem_inode_info *info, pgoff_t index);
static int shmem_swapin_page(struct inode *inode, pgoff_t index,
                             struct page **pagep, enum sgp_type sgp,
                             gfp_t gfp, struct vm_area_struct *vma,
                             vm_fault_t *fault_type);
static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
                struct page **pagep, enum sgp_type sgp,
                gfp_t gfp, struct vm_area_struct *vma,
                struct vm_fault *vmf, vm_fault_t *fault_type);

int shmem_getpage(struct inode *inode, pgoff_t index,
                struct page **pagep, enum sgp_type sgp)
{
        return shmem_getpage_gfp(inode, index, pagep, sgp,
                mapping_gfp_mask(inode->i_mapping), NULL, NULL, NULL);
}

static inline struct shmem_sb_info *SHMEM_SB(struct super_block *sb)
{
        return sb->s_fs_info;
}

/*
 * shmem_file_setup pre-accounts the whole fixed size of a VM object,
 * for shared memory and for shared anonymous (/dev/zero) mappings
 * (unless MAP_NORESERVE and sysctl_overcommit_memory <= 1),
 * consistent with the pre-accounting of private mappings ...
 */
static inline int shmem_acct_size(unsigned long flags, loff_t size)
{
        return (flags & VM_NORESERVE) ?
                0 : security_vm_enough_memory_mm(current->mm, VM_ACCT(size));
}

static inline void shmem_unacct_size(unsigned long flags, loff_t size)
{
        if (!(flags & VM_NORESERVE))
                vm_unacct_memory(VM_ACCT(size));
}

static inline int shmem_reacct_size(unsigned long flags,
                loff_t oldsize, loff_t newsize)
{
        if (!(flags & VM_NORESERVE)) {
                if (VM_ACCT(newsize) > VM_ACCT(oldsize))
                        return security_vm_enough_memory_mm(current->mm,
                                        VM_ACCT(newsize) - VM_ACCT(oldsize));
                else if (VM_ACCT(newsize) < VM_ACCT(oldsize))
                        vm_unacct_memory(VM_ACCT(oldsize) - VM_ACCT(newsize));
        }
        return 0;
}

/*
 * ... whereas tmpfs objects are accounted incrementally as
 * pages are allocated, in order to allow large sparse files.
 * shmem_getpage reports shmem_acct_block failure as -ENOSPC not -ENOMEM,
 * so that a failure on a sparse tmpfs mapping will give SIGBUS not OOM.
 */
static inline int shmem_acct_block(unsigned long flags, long pages)
{
        if (!(flags & VM_NORESERVE))
                return 0;

        return security_vm_enough_memory_mm(current->mm,
                        pages * VM_ACCT(PAGE_SIZE));
}

static inline void shmem_unacct_blocks(unsigned long flags, long pages)
{
        if (flags & VM_NORESERVE)
                vm_unacct_memory(pages * VM_ACCT(PAGE_SIZE));
}

static inline bool shmem_inode_acct_block(struct inode *inode, long pages)
{
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);

        if (shmem_acct_block(info->flags, pages))
                return false;

        if (sbinfo->max_blocks) {
                if (percpu_counter_compare(&sbinfo->used_blocks,
                                           sbinfo->max_blocks - pages) > 0)
                        goto unacct;
                percpu_counter_add(&sbinfo->used_blocks, pages);
        }

        return true;

unacct:
        shmem_unacct_blocks(info->flags, pages);
        return false;
}

static inline void shmem_inode_unacct_blocks(struct inode *inode, long pages)
{
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);

        if (sbinfo->max_blocks)
                percpu_counter_sub(&sbinfo->used_blocks, pages);
        shmem_unacct_blocks(info->flags, pages);
}

static const struct super_operations shmem_ops;
static const struct address_space_operations shmem_aops;
static const struct file_operations shmem_file_operations;
static const struct inode_operations shmem_inode_operations;
static const struct inode_operations shmem_dir_inode_operations;
static const struct inode_operations shmem_special_inode_operations;
static const struct vm_operations_struct shmem_vm_ops;
static struct file_system_type shmem_fs_type;

bool vma_is_shmem(struct vm_area_struct *vma)
{
        return vma->vm_ops == &shmem_vm_ops;
}

static LIST_HEAD(shmem_swaplist);
static DEFINE_MUTEX(shmem_swaplist_mutex);

static int shmem_reserve_inode(struct super_block *sb)
{
        struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
        if (sbinfo->max_inodes) {
                spin_lock(&sbinfo->stat_lock);
                if (!sbinfo->free_inodes) {
                        spin_unlock(&sbinfo->stat_lock);
                        return -ENOSPC;
                }
                sbinfo->free_inodes--;
                spin_unlock(&sbinfo->stat_lock);
        }
        return 0;
}

static void shmem_free_inode(struct super_block *sb)
{
        struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
        if (sbinfo->max_inodes) {
                spin_lock(&sbinfo->stat_lock);
                sbinfo->free_inodes++;
                spin_unlock(&sbinfo->stat_lock);
        }
}

/**
 * shmem_recalc_inode - recalculate the block usage of an inode
 * @inode: inode to recalc
 *
 * We have to calculate the free blocks since the mm can drop
 * undirtied hole pages behind our back.
 *
 * But normally   info->alloced == inode->i_mapping->nrpages + info->swapped
 * So mm freed is info->alloced - (inode->i_mapping->nrpages + info->swapped)
 *
 * It has to be called with the spinlock held.
 */
static void shmem_recalc_inode(struct inode *inode)
{
        struct shmem_inode_info *info = SHMEM_I(inode);
        long freed;

        freed = info->alloced - info->swapped - inode->i_mapping->nrpages;
        if (freed > 0) {
                info->alloced -= freed;
                inode->i_blocks -= freed * BLOCKS_PER_PAGE;
                shmem_inode_unacct_blocks(inode, freed);
        }
}

bool shmem_charge(struct inode *inode, long pages)
{
        struct shmem_inode_info *info = SHMEM_I(inode);
        unsigned long flags;

        if (!shmem_inode_acct_block(inode, pages))
                return false;

        /* nrpages adjustment first, then shmem_recalc_inode() when balanced */
        inode->i_mapping->nrpages += pages;

        spin_lock_irqsave(&info->lock, flags);
        info->alloced += pages;
        inode->i_blocks += pages * BLOCKS_PER_PAGE;
        shmem_recalc_inode(inode);
        spin_unlock_irqrestore(&info->lock, flags);

        return true;
}

void shmem_uncharge(struct inode *inode, long pages)
{
        struct shmem_inode_info *info = SHMEM_I(inode);
        unsigned long flags;

        /* nrpages adjustment done by __delete_from_page_cache() or caller */

        spin_lock_irqsave(&info->lock, flags);
        info->alloced -= pages;
        inode->i_blocks -= pages * BLOCKS_PER_PAGE;
        shmem_recalc_inode(inode);
        spin_unlock_irqrestore(&info->lock, flags);

        shmem_inode_unacct_blocks(inode, pages);
}

/*
 * Replace item expected in xarray by a new item, while holding xa_lock.
 */
static int shmem_replace_entry(struct address_space *mapping,
                        pgoff_t index, void *expected, void *replacement)
{
        XA_STATE(xas, &mapping->i_pages, index);
        void *item;

        VM_BUG_ON(!expected);
        VM_BUG_ON(!replacement);
        item = xas_load(&xas);
        if (item != expected)
                return -ENOENT;
        xas_store(&xas, replacement);
        return 0;
}

/*
 * Sometimes, before we decide whether to proceed or to fail, we must check
 * that an entry was not already brought back from swap by a racing thread.
 *
 * Checking page is not enough: by the time a SwapCache page is locked, it
 * might be reused, and again be SwapCache, using the same swap as before.
 */
static bool shmem_confirm_swap(struct address_space *mapping,
                               pgoff_t index, swp_entry_t swap)
{
        return xa_load(&mapping->i_pages, index) == swp_to_radix_entry(swap);
}

/*
 * Definitions for "huge tmpfs": tmpfs mounted with the huge= option
 *
 * SHMEM_HUGE_NEVER:
 *      disables huge pages for the mount;
 * SHMEM_HUGE_ALWAYS:
 *      enables huge pages for the mount;
 * SHMEM_HUGE_WITHIN_SIZE:
 *      only allocate huge pages if the page will be fully within i_size,
 *      also respect fadvise()/madvise() hints;
 * SHMEM_HUGE_ADVISE:
 *      only allocate huge pages if requested with fadvise()/madvise();
 */

#define SHMEM_HUGE_NEVER        0
#define SHMEM_HUGE_ALWAYS       1
#define SHMEM_HUGE_WITHIN_SIZE  2
#define SHMEM_HUGE_ADVISE       3

/*
 * Special values.
 * Only can be set via /sys/kernel/mm/transparent_hugepage/shmem_enabled:
 *
 * SHMEM_HUGE_DENY:
 *      disables huge on shm_mnt and all mounts, for emergency use;
 * SHMEM_HUGE_FORCE:
 *      enables huge on shm_mnt and all mounts, w/o needing option, for testing;
 *
 */
#define SHMEM_HUGE_DENY         (-1)
#define SHMEM_HUGE_FORCE        (-2)

#ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
/* ifdef here to avoid bloating shmem.o when not necessary */

static int shmem_huge __read_mostly;

#if defined(CONFIG_SYSFS) || defined(CONFIG_TMPFS)
static int shmem_parse_huge(const char *str)
{
        if (!strcmp(str, "never"))
                return SHMEM_HUGE_NEVER;
        if (!strcmp(str, "always"))
                return SHMEM_HUGE_ALWAYS;
        if (!strcmp(str, "within_size"))
                return SHMEM_HUGE_WITHIN_SIZE;
        if (!strcmp(str, "advise"))
                return SHMEM_HUGE_ADVISE;
        if (!strcmp(str, "deny"))
                return SHMEM_HUGE_DENY;
        if (!strcmp(str, "force"))
                return SHMEM_HUGE_FORCE;
        return -EINVAL;
}

static const char *shmem_format_huge(int huge)
{
        switch (huge) {
        case SHMEM_HUGE_NEVER:
                return "never";
        case SHMEM_HUGE_ALWAYS:
                return "always";
        case SHMEM_HUGE_WITHIN_SIZE:
                return "within_size";
        case SHMEM_HUGE_ADVISE:
                return "advise";
        case SHMEM_HUGE_DENY:
                return "deny";
        case SHMEM_HUGE_FORCE:
                return "force";
        default:
                VM_BUG_ON(1);
                return "bad_val";
        }
}
#endif

static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo,
                struct shrink_control *sc, unsigned long nr_to_split)
{
        LIST_HEAD(list), *pos, *next;
        LIST_HEAD(to_remove);
        struct inode *inode;
        struct shmem_inode_info *info;
        struct page *page;
        unsigned long batch = sc ? sc->nr_to_scan : 128;
        int removed = 0, split = 0;

        if (list_empty(&sbinfo->shrinklist))
                return SHRINK_STOP;

        spin_lock(&sbinfo->shrinklist_lock);
        list_for_each_safe(pos, next, &sbinfo->shrinklist) {
                info = list_entry(pos, struct shmem_inode_info, shrinklist);

                /* pin the inode */
                inode = igrab(&info->vfs_inode);

                /* inode is about to be evicted */
                if (!inode) {
                        list_del_init(&info->shrinklist);
                        removed++;
                        goto next;
                }

                /* Check if there's anything to gain */
                if (round_up(inode->i_size, PAGE_SIZE) ==
                                round_up(inode->i_size, HPAGE_PMD_SIZE)) {
                        list_move(&info->shrinklist, &to_remove);
                        removed++;
                        goto next;
                }

                list_move(&info->shrinklist, &list);
next:
                if (!--batch)
                        break;
        }
        spin_unlock(&sbinfo->shrinklist_lock);

        list_for_each_safe(pos, next, &to_remove) {
                info = list_entry(pos, struct shmem_inode_info, shrinklist);
                inode = &info->vfs_inode;
                list_del_init(&info->shrinklist);
                iput(inode);
        }

        list_for_each_safe(pos, next, &list) {
                int ret;

                info = list_entry(pos, struct shmem_inode_info, shrinklist);
                inode = &info->vfs_inode;

                if (nr_to_split && split >= nr_to_split)
                        goto leave;

                page = find_get_page(inode->i_mapping,
                                (inode->i_size & HPAGE_PMD_MASK) >> PAGE_SHIFT);
                if (!page)
                        goto drop;

                /* No huge page at the end of the file: nothing to split */
                if (!PageTransHuge(page)) {
                        put_page(page);
                        goto drop;
                }

                /*
                 * Leave the inode on the list if we failed to lock
                 * the page at this time.
                 *
                 * Waiting for the lock may lead to deadlock in the
                 * reclaim path.
                 */
                if (!trylock_page(page)) {
                        put_page(page);
                        goto leave;
                }

                ret = split_huge_page(page);
                unlock_page(page);
                put_page(page);

                /* If split failed leave the inode on the list */
                if (ret)
                        goto leave;

                split++;
drop:
                list_del_init(&info->shrinklist);
                removed++;
leave:
                iput(inode);
        }

        spin_lock(&sbinfo->shrinklist_lock);
        list_splice_tail(&list, &sbinfo->shrinklist);
        sbinfo->shrinklist_len -= removed;
        spin_unlock(&sbinfo->shrinklist_lock);

        return split;
}

static long shmem_unused_huge_scan(struct super_block *sb,
                struct shrink_control *sc)
{
        struct shmem_sb_info *sbinfo = SHMEM_SB(sb);

        if (!READ_ONCE(sbinfo->shrinklist_len))
                return SHRINK_STOP;

        return shmem_unused_huge_shrink(sbinfo, sc, 0);
}

static long shmem_unused_huge_count(struct super_block *sb,
                struct shrink_control *sc)
{
        struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
        return READ_ONCE(sbinfo->shrinklist_len);
}
#else /* !CONFIG_TRANSPARENT_HUGE_PAGECACHE */

#define shmem_huge SHMEM_HUGE_DENY

static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo,
                struct shrink_control *sc, unsigned long nr_to_split)
{
        return 0;
}
#endif /* CONFIG_TRANSPARENT_HUGE_PAGECACHE */

static inline bool is_huge_enabled(struct shmem_sb_info *sbinfo)
{
        if (IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE) &&
            (shmem_huge == SHMEM_HUGE_FORCE || sbinfo->huge) &&
            shmem_huge != SHMEM_HUGE_DENY)
                return true;
        return false;
}

/*
 * Like add_to_page_cache_locked, but error if expected item has gone.
 */
static int shmem_add_to_page_cache(struct page *page,
                                   struct address_space *mapping,
                                   pgoff_t index, void *expected, gfp_t gfp)
{
        XA_STATE_ORDER(xas, &mapping->i_pages, index, compound_order(page));
        unsigned long i = 0;
        unsigned long nr = 1UL << compound_order(page);

        VM_BUG_ON_PAGE(PageTail(page), page);
        VM_BUG_ON_PAGE(index != round_down(index, nr), page);
        VM_BUG_ON_PAGE(!PageLocked(page), page);
        VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
        VM_BUG_ON(expected && PageTransHuge(page));

        page_ref_add(page, nr);
        page->mapping = mapping;
        page->index = index;

        do {
                void *entry;
                xas_lock_irq(&xas);
                entry = xas_find_conflict(&xas);
                if (entry != expected)
                        xas_set_err(&xas, -EEXIST);
                xas_create_range(&xas);
                if (xas_error(&xas))
                        goto unlock;
next:
                xas_store(&xas, page + i);
                if (++i < nr) {
                        xas_next(&xas);
                        goto next;
                }
                if (PageTransHuge(page)) {
                        count_vm_event(THP_FILE_ALLOC);
                        __inc_node_page_state(page, NR_SHMEM_THPS);
                }
                mapping->nrpages += nr;
                __mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
                __mod_node_page_state(page_pgdat(page), NR_SHMEM, nr);
unlock:
                xas_unlock_irq(&xas);
        } while (xas_nomem(&xas, gfp));

        if (xas_error(&xas)) {
                page->mapping = NULL;
                page_ref_sub(page, nr);
                return xas_error(&xas);
        }

        return 0;
}

/*
 * Like delete_from_page_cache, but substitutes swap for page.
 */
static void shmem_delete_from_page_cache(struct page *page, void *radswap)
{
        struct address_space *mapping = page->mapping;
        int error;

        VM_BUG_ON_PAGE(PageCompound(page), page);

        xa_lock_irq(&mapping->i_pages);
        error = shmem_replace_entry(mapping, page->index, page, radswap);
        page->mapping = NULL;
        mapping->nrpages--;
        __dec_node_page_state(page, NR_FILE_PAGES);
        __dec_node_page_state(page, NR_SHMEM);
        xa_unlock_irq(&mapping->i_pages);
        put_page(page);
        BUG_ON(error);
}

/*
 * Remove swap entry from page cache, free the swap and its page cache.
 */
static int shmem_free_swap(struct address_space *mapping,
                           pgoff_t index, void *radswap)
{
        void *old;

        old = xa_cmpxchg_irq(&mapping->i_pages, index, radswap, NULL, 0);
        if (old != radswap)
                return -ENOENT;
        free_swap_and_cache(radix_to_swp_entry(radswap));
        return 0;
}

/*
 * Determine (in bytes) how many of the shmem object's pages mapped by the
 * given offsets are swapped out.
 *
 * This is safe to call without i_mutex or the i_pages lock thanks to RCU,
 * as long as the inode doesn't go away and racy results are not a problem.
 */
unsigned long shmem_partial_swap_usage(struct address_space *mapping,
                                                pgoff_t start, pgoff_t end)
{
        XA_STATE(xas, &mapping->i_pages, start);
        struct page *page;
        unsigned long swapped = 0;

        rcu_read_lock();
        xas_for_each(&xas, page, end - 1) {
                if (xas_retry(&xas, page))
                        continue;
                if (xa_is_value(page))
                        swapped++;

                if (need_resched()) {
                        xas_pause(&xas);
                        cond_resched_rcu();
                }
        }

        rcu_read_unlock();

        return swapped << PAGE_SHIFT;
}

/*
 * Determine (in bytes) how many of the shmem object's pages mapped by the
 * given vma is swapped out.
 *
 * This is safe to call without i_mutex or the i_pages lock thanks to RCU,
 * as long as the inode doesn't go away and racy results are not a problem.
 */
unsigned long shmem_swap_usage(struct vm_area_struct *vma)
{
        struct inode *inode = file_inode(vma->vm_file);
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct address_space *mapping = inode->i_mapping;
        unsigned long swapped;

        /* Be careful as we don't hold info->lock */
        swapped = READ_ONCE(info->swapped);

        /*
         * The easier cases are when the shmem object has nothing in swap, or
         * the vma maps it whole. Then we can simply use the stats that we
         * already track.
         */
        if (!swapped)
                return 0;

        if (!vma->vm_pgoff && vma->vm_end - vma->vm_start >= inode->i_size)
                return swapped << PAGE_SHIFT;

        /* Here comes the more involved part */
        return shmem_partial_swap_usage(mapping,
                        linear_page_index(vma, vma->vm_start),
                        linear_page_index(vma, vma->vm_end));
}

/*
 * SysV IPC SHM_UNLOCK restore Unevictable pages to their evictable lists.
 */
void shmem_unlock_mapping(struct address_space *mapping)
{
        struct pagevec pvec;
        pgoff_t indices[PAGEVEC_SIZE];
        pgoff_t index = 0;

        pagevec_init(&pvec);
        /*
         * Minor point, but we might as well stop if someone else SHM_LOCKs it.
         */
        while (!mapping_unevictable(mapping)) {
                /*
                 * Avoid pagevec_lookup(): find_get_pages() returns 0 as if it
                 * has finished, if it hits a row of PAGEVEC_SIZE swap entries.
                 */
                pvec.nr = find_get_entries(mapping, index,
                                           PAGEVEC_SIZE, pvec.pages, indices);
                if (!pvec.nr)
                        break;
                index = indices[pvec.nr - 1] + 1;
                pagevec_remove_exceptionals(&pvec);
                check_move_unevictable_pages(&pvec);
                pagevec_release(&pvec);
                cond_resched();
        }
}

/*
 * Remove range of pages and swap entries from page cache, and free them.
 * If !unfalloc, truncate or punch hole; if unfalloc, undo failed fallocate.
 */
static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
                                                                 bool unfalloc)
{
        struct address_space *mapping = inode->i_mapping;
        struct shmem_inode_info *info = SHMEM_I(inode);
        pgoff_t start = (lstart + PAGE_SIZE - 1) >> PAGE_SHIFT;
        pgoff_t end = (lend + 1) >> PAGE_SHIFT;
        unsigned int partial_start = lstart & (PAGE_SIZE - 1);
        unsigned int partial_end = (lend + 1) & (PAGE_SIZE - 1);
        struct pagevec pvec;
        pgoff_t indices[PAGEVEC_SIZE];
        long nr_swaps_freed = 0;
        pgoff_t index;
        int i;

        if (lend == -1)
                end = -1;       /* unsigned, so actually very big */

        pagevec_init(&pvec);
        index = start;
        while (index < end) {
                pvec.nr = find_get_entries(mapping, index,
                        min(end - index, (pgoff_t)PAGEVEC_SIZE),
                        pvec.pages, indices);
                if (!pvec.nr)
                        break;
                for (i = 0; i < pagevec_count(&pvec); i++) {
                        struct page *page = pvec.pages[i];

                        index = indices[i];
                        if (index >= end)
                                break;

                        if (xa_is_value(page)) {
                                if (unfalloc)
                                        continue;
                                nr_swaps_freed += !shmem_free_swap(mapping,
                                                                index, page);
                                continue;
                        }

                        VM_BUG_ON_PAGE(page_to_pgoff(page) != index, page);

                        if (!trylock_page(page))
                                continue;

                        if (PageTransTail(page)) {
                                /* Middle of THP: zero out the page */
                                clear_highpage(page);
                                unlock_page(page);
                                continue;
                        } else if (PageTransHuge(page)) {
                                if (index == round_down(end, HPAGE_PMD_NR)) {
                                        /*
                                         * Range ends in the middle of THP:
                                         * zero out the page
                                         */
                                        clear_highpage(page);
                                        unlock_page(page);
                                        continue;
                                }
                                index += HPAGE_PMD_NR - 1;
                                i += HPAGE_PMD_NR - 1;
                        }

                        if (!unfalloc || !PageUptodate(page)) {
                                VM_BUG_ON_PAGE(PageTail(page), page);
                                if (page_mapping(page) == mapping) {
                                        VM_BUG_ON_PAGE(PageWriteback(page), page);
                                        truncate_inode_page(mapping, page);
                                }
                        }
                        unlock_page(page);
                }
                pagevec_remove_exceptionals(&pvec);
                pagevec_release(&pvec);
                cond_resched();
                index++;
        }

        if (partial_start) {
                struct page *page = NULL;
                shmem_getpage(inode, start - 1, &page, SGP_READ);
                if (page) {
                        unsigned int top = PAGE_SIZE;
                        if (start > end) {
                                top = partial_end;
                                partial_end = 0;
                        }
                        zero_user_segment(page, partial_start, top);
                        set_page_dirty(page);
                        unlock_page(page);
                        put_page(page);
                }
        }
        if (partial_end) {
                struct page *page = NULL;
                shmem_getpage(inode, end, &page, SGP_READ);
                if (page) {
                        zero_user_segment(page, 0, partial_end);
                        set_page_dirty(page);
                        unlock_page(page);
                        put_page(page);
                }
        }
        if (start >= end)
                return;

        index = start;
        while (index < end) {
                cond_resched();

                pvec.nr = find_get_entries(mapping, index,
                                min(end - index, (pgoff_t)PAGEVEC_SIZE),
                                pvec.pages, indices);
                if (!pvec.nr) {
                        /* If all gone or hole-punch or unfalloc, we're done */
                        if (index == start || end != -1)
                                break;
                        /* But if truncating, restart to make sure all gone */
                        index = start;
                        continue;
                }
                for (i = 0; i < pagevec_count(&pvec); i++) {
                        struct page *page = pvec.pages[i];

                        index = indices[i];
                        if (index >= end)
                                break;

                        if (xa_is_value(page)) {
                                if (unfalloc)
                                        continue;
                                if (shmem_free_swap(mapping, index, page)) {
                                        /* Swap was replaced by page: retry */
                                        index--;
                                        break;
                                }
                                nr_swaps_freed++;
                                continue;
                        }

                        lock_page(page);

                        if (PageTransTail(page)) {
                                /* Middle of THP: zero out the page */
                                clear_highpage(page);
                                unlock_page(page);
                                /*
                                 * Partial thp truncate due 'start' in middle
                                 * of THP: don't need to look on these pages
                                 * again on !pvec.nr restart.
                                 */
                                if (index != round_down(end, HPAGE_PMD_NR))
                                        start++;
                                continue;
                        } else if (PageTransHuge(page)) {
                                if (index == round_down(end, HPAGE_PMD_NR)) {
                                        /*
                                         * Range ends in the middle of THP:
                                         * zero out the page
                                         */
                                        clear_highpage(page);
                                        unlock_page(page);
                                        continue;
                                }
                                index += HPAGE_PMD_NR - 1;
                                i += HPAGE_PMD_NR - 1;
                        }

                        if (!unfalloc || !PageUptodate(page)) {
                                VM_BUG_ON_PAGE(PageTail(page), page);
                                if (page_mapping(page) == mapping) {
                                        VM_BUG_ON_PAGE(PageWriteback(page), page);
                                        truncate_inode_page(mapping, page);
                                } else {
                                        /* Page was replaced by swap: retry */
                                        unlock_page(page);
                                        index--;
                                        break;
                                }
                        }
                        unlock_page(page);
                }
                pagevec_remove_exceptionals(&pvec);
                pagevec_release(&pvec);
                index++;
        }

        spin_lock_irq(&info->lock);
        info->swapped -= nr_swaps_freed;
        shmem_recalc_inode(inode);
        spin_unlock_irq(&info->lock);
}

void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
{
        shmem_undo_range(inode, lstart, lend, false);
        inode->i_ctime = inode->i_mtime = current_time(inode);
}
EXPORT_SYMBOL_GPL(shmem_truncate_range);

static int shmem_getattr(const struct path *path, struct kstat *stat,
                         u32 request_mask, unsigned int query_flags)
{
        struct inode *inode = path->dentry->d_inode;
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct shmem_sb_info *sb_info = SHMEM_SB(inode->i_sb);

        if (info->alloced - info->swapped != inode->i_mapping->nrpages) {
                spin_lock_irq(&info->lock);
                shmem_recalc_inode(inode);
                spin_unlock_irq(&info->lock);
        }
        generic_fillattr(inode, stat);

        if (is_huge_enabled(sb_info))
                stat->blksize = HPAGE_PMD_SIZE;

        return 0;
}

static int shmem_setattr(struct dentry *dentry, struct iattr *attr)

{
        struct inode *inode = d_inode(dentry);
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
        int error;

        error = setattr_prepare(dentry, attr);
        if (error)
                return error;

        if (S_ISREG(inode->i_mode) && (attr->ia_valid & ATTR_SIZE)) {
                loff_t oldsize = inode->i_size;
                loff_t newsize = attr->ia_size;

                /* protected by i_mutex */
                if ((newsize < oldsize && (info->seals & F_SEAL_SHRINK)) ||
                    (newsize > oldsize && (info->seals & F_SEAL_GROW)))
                        return -EPERM;

                if (newsize != oldsize) {
                        error = shmem_reacct_size(SHMEM_I(inode)->flags,
                                        oldsize, newsize);
                        if (error)
                                return error;
                        i_size_write(inode, newsize);
                        inode->i_ctime = inode->i_mtime = current_time(inode);
                }
                if (newsize <= oldsize) {
                        loff_t holebegin = round_up(newsize, PAGE_SIZE);
                        if (oldsize > holebegin)
                                unmap_mapping_range(inode->i_mapping,
                                                        holebegin, 0, 1);
                        if (info->alloced)
                                shmem_truncate_range(inode,
                                                        newsize, (loff_t)-1);
                        /* unmap again to remove racily COWed private pages */
                        if (oldsize > holebegin)
                                unmap_mapping_range(inode->i_mapping,
                                                        holebegin, 0, 1);

                        /*
                         * Part of the huge page can be beyond i_size: subject
                         * to shrink under memory pressure.
                         */
                        if (IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE)) {
                                spin_lock(&sbinfo->shrinklist_lock);
                                /*
                                 * _careful to defend against unlocked access to
                                 * ->shrink_list in shmem_unused_huge_shrink()
                                 */
                                if (list_empty_careful(&info->shrinklist)) {
                                        list_add_tail(&info->shrinklist,
                                                        &sbinfo->shrinklist);
                                        sbinfo->shrinklist_len++;
                                }
                                spin_unlock(&sbinfo->shrinklist_lock);
                        }
                }
        }

        setattr_copy(inode, attr);
        if (attr->ia_valid & ATTR_MODE)
                error = posix_acl_chmod(inode, inode->i_mode);
        return error;
}

static void shmem_evict_inode(struct inode *inode)
{
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);

        if (inode->i_mapping->a_ops == &shmem_aops) {
                shmem_unacct_size(info->flags, inode->i_size);
                inode->i_size = 0;
                shmem_truncate_range(inode, 0, (loff_t)-1);
                if (!list_empty(&info->shrinklist)) {
                        spin_lock(&sbinfo->shrinklist_lock);
                        if (!list_empty(&info->shrinklist)) {
                                list_del_init(&info->shrinklist);
                                sbinfo->shrinklist_len--;
                        }
                        spin_unlock(&sbinfo->shrinklist_lock);
                }
                while (!list_empty(&info->swaplist)) {
                        /* Wait while shmem_unuse() is scanning this inode... */
                        wait_var_event(&info->stop_eviction,
                                       !atomic_read(&info->stop_eviction));
                        mutex_lock(&shmem_swaplist_mutex);
                        /* ...but beware of the race if we peeked too early */
                        if (!atomic_read(&info->stop_eviction))
                                list_del_init(&info->swaplist);
                        mutex_unlock(&shmem_swaplist_mutex);
                }
        }

        simple_xattrs_free(&info->xattrs);
        WARN_ON(inode->i_blocks);
        shmem_free_inode(inode->i_sb);
        clear_inode(inode);
}

extern struct swap_info_struct *swap_info[];

static int shmem_find_swap_entries(struct address_space *mapping,
                                   pgoff_t start, unsigned int nr_entries,
                                   struct page **entries, pgoff_t *indices,
                                   unsigned int type, bool frontswap)
{
        XA_STATE(xas, &mapping->i_pages, start);
        struct page *page;
        swp_entry_t entry;
        unsigned int ret = 0;

        if (!nr_entries)
                return 0;

        rcu_read_lock();
        xas_for_each(&xas, page, ULONG_MAX) {
                if (xas_retry(&xas, page))
                        continue;

                if (!xa_is_value(page))
                        continue;

                entry = radix_to_swp_entry(page);
                if (swp_type(entry) != type)
                        continue;
                if (frontswap &&
                    !frontswap_test(swap_info[type], swp_offset(entry)))
                        continue;

                indices[ret] = xas.xa_index;
                entries[ret] = page;

                if (need_resched()) {
                        xas_pause(&xas);
                        cond_resched_rcu();
                }
                if (++ret == nr_entries)
                        break;
        }
        rcu_read_unlock();

        return ret;
}

/*
 * Move the swapped pages for an inode to page cache. Returns the count
 * of pages swapped in, or the error in case of failure.
 */
static int shmem_unuse_swap_entries(struct inode *inode, struct pagevec pvec,
                                    pgoff_t *indices)
{
        int i = 0;
        int ret = 0;
        int error = 0;
        struct address_space *mapping = inode->i_mapping;

        for (i = 0; i < pvec.nr; i++) {
                struct page *page = pvec.pages[i];

                if (!xa_is_value(page))
                        continue;
                error = shmem_swapin_page(inode, indices[i],
                                          &page, SGP_CACHE,
                                          mapping_gfp_mask(mapping),
                                          NULL, NULL);
                if (error == 0) {
                        unlock_page(page);
                        put_page(page);
                        ret++;
                }
                if (error == -ENOMEM)
                        break;
                error = 0;
        }
        return error ? error : ret;
}

/*
 * If swap found in inode, free it and move page from swapcache to filecache.
 */
static int shmem_unuse_inode(struct inode *inode, unsigned int type,
                             bool frontswap, unsigned long *fs_pages_to_unuse)
{
        struct address_space *mapping = inode->i_mapping;
        pgoff_t start = 0;
        struct pagevec pvec;
        pgoff_t indices[PAGEVEC_SIZE];
        bool frontswap_partial = (frontswap && *fs_pages_to_unuse > 0);
        int ret = 0;

        pagevec_init(&pvec);
        do {
                unsigned int nr_entries = PAGEVEC_SIZE;

                if (frontswap_partial && *fs_pages_to_unuse < PAGEVEC_SIZE)
                        nr_entries = *fs_pages_to_unuse;

                pvec.nr = shmem_find_swap_entries(mapping, start, nr_entries,
                                                  pvec.pages, indices,
                                                  type, frontswap);
                if (pvec.nr == 0) {
                        ret = 0;
                        break;
                }

                ret = shmem_unuse_swap_entries(inode, pvec, indices);
                if (ret < 0)
                        break;

                if (frontswap_partial) {
                        *fs_pages_to_unuse -= ret;
                        if (*fs_pages_to_unuse == 0) {
                                ret = FRONTSWAP_PAGES_UNUSED;
                                break;
                        }
                }

                start = indices[pvec.nr - 1];
        } while (true);

        return ret;
}

/*
 * Read all the shared memory data that resides in the swap
 * device 'type' back into memory, so the swap device can be
 * unused.
 */
int shmem_unuse(unsigned int type, bool frontswap,
                unsigned long *fs_pages_to_unuse)
{
        struct shmem_inode_info *info, *next;
        int error = 0;

        if (list_empty(&shmem_swaplist))
                return 0;

        mutex_lock(&shmem_swaplist_mutex);
        list_for_each_entry_safe(info, next, &shmem_swaplist, swaplist) {
                if (!info->swapped) {
                        list_del_init(&info->swaplist);
                        continue;
                }
                /*
                 * Drop the swaplist mutex while searching the inode for swap;
                 * but before doing so, make sure shmem_evict_inode() will not
                 * remove placeholder inode from swaplist, nor let it be freed
                 * (igrab() would protect from unlink, but not from unmount).
                 */
                atomic_inc(&info->stop_eviction);
                mutex_unlock(&shmem_swaplist_mutex);

                error = shmem_unuse_inode(&info->vfs_inode, type, frontswap,
                                          fs_pages_to_unuse);
                cond_resched();

                mutex_lock(&shmem_swaplist_mutex);
                next = list_next_entry(info, swaplist);
                if (!info->swapped)
                        list_del_init(&info->swaplist);
                if (atomic_dec_and_test(&info->stop_eviction))
                        wake_up_var(&info->stop_eviction);
                if (error)
                        break;
        }
        mutex_unlock(&shmem_swaplist_mutex);

        return error;
}

/*
 * Move the page from the page cache to the swap cache.
 */
static int shmem_writepage(struct page *page, struct writeback_control *wbc)
{
        struct shmem_inode_info *info;
        struct address_space *mapping;
        struct inode *inode;
        swp_entry_t swap;
        pgoff_t index;

        VM_BUG_ON_PAGE(PageCompound(page), page);
        BUG_ON(!PageLocked(page));
        mapping = page->mapping;
        index = page->index;
        inode = mapping->host;
        info = SHMEM_I(inode);
        if (info->flags & VM_LOCKED)
                goto redirty;
        if (!total_swap_pages)
                goto redirty;

        /*
         * Our capabilities prevent regular writeback or sync from ever calling
         * shmem_writepage; but a stacking filesystem might use ->writepage of
         * its underlying filesystem, in which case tmpfs should write out to
         * swap only in response to memory pressure, and not for the writeback
         * threads or sync.
         */
        if (!wbc->for_reclaim) {
                WARN_ON_ONCE(1);        /* Still happens? Tell us about it! */
                goto redirty;
        }

        /*
         * This is somewhat ridiculous, but without plumbing a SWAP_MAP_FALLOC
         * value into swapfile.c, the only way we can correctly account for a
         * fallocated page arriving here is now to initialize it and write it.
         *
         * That's okay for a page already fallocated earlier, but if we have
         * not yet completed the fallocation, then (a) we want to keep track
         * of this page in case we have to undo it, and (b) it may not be a
         * good idea to continue anyway, once we're pushing into swap.  So
         * reactivate the page, and let shmem_fallocate() quit when too many.
         */
        if (!PageUptodate(page)) {
                if (inode->i_private) {
                        struct shmem_falloc *shmem_falloc;
                        spin_lock(&inode->i_lock);
                        shmem_falloc = inode->i_private;
                        if (shmem_falloc &&
                            !shmem_falloc->waitq &&
                            index >= shmem_falloc->start &&
                            index < shmem_falloc->next)
                                shmem_falloc->nr_unswapped++;
                        else
                                shmem_falloc = NULL;
                        spin_unlock(&inode->i_lock);
                        if (shmem_falloc)
                                goto redirty;
                }
                clear_highpage(page);
                flush_dcache_page(page);
                SetPageUptodate(page);
        }

        swap = get_swap_page(page);
        if (!swap.val)
                goto redirty;

        /*
         * Add inode to shmem_unuse()'s list of swapped-out inodes,
         * if it's not already there.  Do it now before the page is
         * moved to swap cache, when its pagelock no longer protects
         * the inode from eviction.  But don't unlock the mutex until
         * we've incremented swapped, because shmem_unuse_inode() will
         * prune a !swapped inode from the swaplist under this mutex.
         */
        mutex_lock(&shmem_swaplist_mutex);
        if (list_empty(&info->swaplist))
                list_add(&info->swaplist, &shmem_swaplist);

        if (add_to_swap_cache(page, swap, GFP_ATOMIC) == 0) {
                spin_lock_irq(&info->lock);
                shmem_recalc_inode(inode);
                info->swapped++;
                spin_unlock_irq(&info->lock);

                swap_shmem_alloc(swap);
                shmem_delete_from_page_cache(page, swp_to_radix_entry(swap));

                mutex_unlock(&shmem_swaplist_mutex);
                BUG_ON(page_mapped(page));
                swap_writepage(page, wbc);
                return 0;
        }

        mutex_unlock(&shmem_swaplist_mutex);
        put_swap_page(page, swap);
redirty:
        set_page_dirty(page);
        if (wbc->for_reclaim)
                return AOP_WRITEPAGE_ACTIVATE;  /* Return with page locked */
        unlock_page(page);
        return 0;
}

#if defined(CONFIG_NUMA) && defined(CONFIG_TMPFS)
static void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
{
        char buffer[64];

        if (!mpol || mpol->mode == MPOL_DEFAULT)
                return;         /* show nothing */

        mpol_to_str(buffer, sizeof(buffer), mpol);

        seq_printf(seq, ",mpol=%s", buffer);
}

static struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
{
        struct mempolicy *mpol = NULL;
        if (sbinfo->mpol) {
                spin_lock(&sbinfo->stat_lock);  /* prevent replace/use races */
                mpol = sbinfo->mpol;
                mpol_get(mpol);
                spin_unlock(&sbinfo->stat_lock);
        }
        return mpol;
}
#else /* !CONFIG_NUMA || !CONFIG_TMPFS */
static inline void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
{
}
static inline struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
{
        return NULL;
}
#endif /* CONFIG_NUMA && CONFIG_TMPFS */
#ifndef CONFIG_NUMA
#define vm_policy vm_private_data
#endif

static void shmem_pseudo_vma_init(struct vm_area_struct *vma,
                struct shmem_inode_info *info, pgoff_t index)
{
        /* Create a pseudo vma that just contains the policy */
        vma_init(vma, NULL);
        /* Bias interleave by inode number to distribute better across nodes */
        vma->vm_pgoff = index + info->vfs_inode.i_ino;
        vma->vm_policy = mpol_shared_policy_lookup(&info->policy, index);
}

static void shmem_pseudo_vma_destroy(struct vm_area_struct *vma)
{
        /* Drop reference taken by mpol_shared_policy_lookup() */
        mpol_cond_put(vma->vm_policy);
}

static struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp,
                        struct shmem_inode_info *info, pgoff_t index)
{
        struct vm_area_struct pvma;
        struct page *page;
        struct vm_fault vmf;

        shmem_pseudo_vma_init(&pvma, info, index);
        vmf.vma = &pvma;
        vmf.address = 0;
        page = swap_cluster_readahead(swap, gfp, &vmf);
        shmem_pseudo_vma_destroy(&pvma);

        return page;
}

static struct page *shmem_alloc_hugepage(gfp_t gfp,
                struct shmem_inode_info *info, pgoff_t index)
{
        struct vm_area_struct pvma;
        struct address_space *mapping = info->vfs_inode.i_mapping;
        pgoff_t hindex;
        struct page *page;

        if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE))
                return NULL;

        hindex = round_down(index, HPAGE_PMD_NR);
        if (xa_find(&mapping->i_pages, &hindex, hindex + HPAGE_PMD_NR - 1,
                                                                XA_PRESENT))
                return NULL;

        shmem_pseudo_vma_init(&pvma, info, hindex);
        page = alloc_pages_vma(gfp | __GFP_COMP | __GFP_NORETRY | __GFP_NOWARN,
                        HPAGE_PMD_ORDER, &pvma, 0, numa_node_id(), true);
        shmem_pseudo_vma_destroy(&pvma);
        if (page)
                prep_transhuge_page(page);
        return page;
}

static struct page *shmem_alloc_page(gfp_t gfp,
                        struct shmem_inode_info *info, pgoff_t index)
{
        struct vm_area_struct pvma;
        struct page *page;

        shmem_pseudo_vma_init(&pvma, info, index);
        page = alloc_page_vma(gfp, &pvma, 0);
        shmem_pseudo_vma_destroy(&pvma);

        return page;
}

static struct page *shmem_alloc_and_acct_page(gfp_t gfp,
                struct inode *inode,
                pgoff_t index, bool huge)
{
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct page *page;
        int nr;
        int err = -ENOSPC;

        if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE))
                huge = false;
        nr = huge ? HPAGE_PMD_NR : 1;

        if (!shmem_inode_acct_block(inode, nr))
                goto failed;

        if (huge)
                page = shmem_alloc_hugepage(gfp, info, index);
        else
                page = shmem_alloc_page(gfp, info, index);
        if (page) {
                __SetPageLocked(page);
                __SetPageSwapBacked(page);
                return page;
        }

        err = -ENOMEM;
        shmem_inode_unacct_blocks(inode, nr);
failed:
        return ERR_PTR(err);
}

/*
 * When a page is moved from swapcache to shmem filecache (either by the
 * usual swapin of shmem_getpage_gfp(), or by the less common swapoff of
 * shmem_unuse_inode()), it may have been read in earlier from swap, in
 * ignorance of the mapping it belongs to.  If that mapping has special
 * constraints (like the gma500 GEM driver, which requires RAM below 4GB),
 * we may need to copy to a suitable page before moving to filecache.
 *
 * In a future release, this may well be extended to respect cpuset and
 * NUMA mempolicy, and applied also to anonymous pages in do_swap_page();
 * but for now it is a simple matter of zone.
 */
static bool shmem_should_replace_page(struct page *page, gfp_t gfp)
{
        return page_zonenum(page) > gfp_zone(gfp);
}

static int shmem_replace_page(struct page **pagep, gfp_t gfp,
                                struct shmem_inode_info *info, pgoff_t index)
{
        struct page *oldpage, *newpage;
        struct address_space *swap_mapping;
        swp_entry_t entry;
        pgoff_t swap_index;
        int error;

        oldpage = *pagep;
        entry.val = page_private(oldpage);
        swap_index = swp_offset(entry);
        swap_mapping = page_mapping(oldpage);

        /*
         * We have arrived here because our zones are constrained, so don't
         * limit chance of success by further cpuset and node constraints.
         */
        gfp &= ~GFP_CONSTRAINT_MASK;
        newpage = shmem_alloc_page(gfp, info, index);
        if (!newpage)
                return -ENOMEM;

        get_page(newpage);
        copy_highpage(newpage, oldpage);
        flush_dcache_page(newpage);

        __SetPageLocked(newpage);
        __SetPageSwapBacked(newpage);
        SetPageUptodate(newpage);
        set_page_private(newpage, entry.val);
        SetPageSwapCache(newpage);

        /*
         * Our caller will very soon move newpage out of swapcache, but it's
         * a nice clean interface for us to replace oldpage by newpage there.
         */
        xa_lock_irq(&swap_mapping->i_pages);
        error = shmem_replace_entry(swap_mapping, swap_index, oldpage, newpage);
        if (!error) {
                __inc_node_page_state(newpage, NR_FILE_PAGES);
                __dec_node_page_state(oldpage, NR_FILE_PAGES);
        }
        xa_unlock_irq(&swap_mapping->i_pages);

        if (unlikely(error)) {
                /*
                 * Is this possible?  I think not, now that our callers check
                 * both PageSwapCache and page_private after getting page lock;
                 * but be defensive.  Reverse old to newpage for clear and free.
                 */
                oldpage = newpage;
        } else {
                mem_cgroup_migrate(oldpage, newpage);
                lru_cache_add_anon(newpage);
                *pagep = newpage;
        }

        ClearPageSwapCache(oldpage);
        set_page_private(oldpage, 0);

        unlock_page(oldpage);
        put_page(oldpage);
        put_page(oldpage);
        return error;
}

/*
 * Swap in the page pointed to by *pagep.
 * Caller has to make sure that *pagep contains a valid swapped page.
 * Returns 0 and the page in pagep if success. On failure, returns the
 * the error code and NULL in *pagep.
 */
static int shmem_swapin_page(struct inode *inode, pgoff_t index,
                             struct page **pagep, enum sgp_type sgp,
                             gfp_t gfp, struct vm_area_struct *vma,
                             vm_fault_t *fault_type)
{
        struct address_space *mapping = inode->i_mapping;
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct mm_struct *charge_mm = vma ? vma->vm_mm : current->mm;
        struct mem_cgroup *memcg;
        struct page *page;
        swp_entry_t swap;
        int error;

        VM_BUG_ON(!*pagep || !xa_is_value(*pagep));
        swap = radix_to_swp_entry(*pagep);
        *pagep = NULL;

        /* Look it up and read it in.. */
        page = lookup_swap_cache(swap, NULL, 0);
        if (!page) {
                /* Or update major stats only when swapin succeeds?? */
                if (fault_type) {
                        *fault_type |= VM_FAULT_MAJOR;
                        count_vm_event(PGMAJFAULT);
                        count_memcg_event_mm(charge_mm, PGMAJFAULT);
                }
                /* Here we actually start the io */
                page = shmem_swapin(swap, gfp, info, index);
                if (!page) {
                        error = -ENOMEM;
                        goto failed;
                }
        }

        /* We have to do this with page locked to prevent races */
        lock_page(page);
        if (!PageSwapCache(page) || page_private(page) != swap.val ||
            !shmem_confirm_swap(mapping, index, swap)) {
                error = -EEXIST;
                goto unlock;
        }
        if (!PageUptodate(page)) {
                error = -EIO;
                goto failed;
        }
        wait_on_page_writeback(page);

        if (shmem_should_replace_page(page, gfp)) {
                error = shmem_replace_page(&page, gfp, info, index);
                if (error)
                        goto failed;
        }

        error = mem_cgroup_try_charge_delay(page, charge_mm, gfp, &memcg,
                                            false);
        if (!error) {
                error = shmem_add_to_page_cache(page, mapping, index,
                                                swp_to_radix_entry(swap), gfp);
                /*
                 * We already confirmed swap under page lock, and make
                 * no memory allocation here, so usually no possibility
                 * of error; but free_swap_and_cache() only trylocks a
                 * page, so it is just possible that the entry has been
                 * truncated or holepunched since swap was confirmed.
                 * shmem_undo_range() will have done some of the
                 * unaccounting, now delete_from_swap_cache() will do
                 * the rest.
                 */
                if (error) {
                        mem_cgroup_cancel_charge(page, memcg, false);
                        delete_from_swap_cache(page);
                }
        }
        if (error)
                goto failed;

        mem_cgroup_commit_charge(page, memcg, true, false);

        spin_lock_irq(&info->lock);
        info->swapped--;
        shmem_recalc_inode(inode);
        spin_unlock_irq(&info->lock);

        if (sgp == SGP_WRITE)
                mark_page_accessed(page);

        delete_from_swap_cache(page);
        set_page_dirty(page);
        swap_free(swap);

        *pagep = page;
        return 0;
failed:
        if (!shmem_confirm_swap(mapping, index, swap))
                error = -EEXIST;
unlock:
        if (page) {
                unlock_page(page);
                put_page(page);
        }

        return error;
}

/*
 * shmem_getpage_gfp - find page in cache, or get from swap, or allocate
 *
 * If we allocate a new one we do not mark it dirty. That's up to the
 * vm. If we swap it in we mark it dirty since we also free the swap
 * entry since a page cannot live in both the swap and page cache.
 *
 * fault_mm and fault_type are only supplied by shmem_fault:
 * otherwise they are NULL.
 */
static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
        struct page **pagep, enum sgp_type sgp, gfp_t gfp,
        struct vm_area_struct *vma, struct vm_fault *vmf,
                        vm_fault_t *fault_type)
{
        struct address_space *mapping = inode->i_mapping;
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct shmem_sb_info *sbinfo;
        struct mm_struct *charge_mm;
        struct mem_cgroup *memcg;
        struct page *page;
        enum sgp_type sgp_huge = sgp;
        pgoff_t hindex = index;
        int error;
        int once = 0;
        int alloced = 0;

        if (index > (MAX_LFS_FILESIZE >> PAGE_SHIFT))
                return -EFBIG;
        if (sgp == SGP_NOHUGE || sgp == SGP_HUGE)
                sgp = SGP_CACHE;
repeat:
        if (sgp <= SGP_CACHE &&
            ((loff_t)index << PAGE_SHIFT) >= i_size_read(inode)) {
                return -EINVAL;
        }

        sbinfo = SHMEM_SB(inode->i_sb);
        charge_mm = vma ? vma->vm_mm : current->mm;

        page = find_lock_entry(mapping, index);
        if (xa_is_value(page)) {
                error = shmem_swapin_page(inode, index, &page,
                                          sgp, gfp, vma, fault_type);
                if (error == -EEXIST)
                        goto repeat;

                *pagep = page;
                return error;
        }

        if (page && sgp == SGP_WRITE)
                mark_page_accessed(page);

        /* fallocated page? */
        if (page && !PageUptodate(page)) {
                if (sgp != SGP_READ)
                        goto clear;
                unlock_page(page);
                put_page(page);
                page = NULL;
        }
        if (page || sgp == SGP_READ) {
                *pagep = page;
                return 0;
        }

        /*
         * Fast cache lookup did not find it:
         * bring it back from swap or allocate.
         */

        if (vma && userfaultfd_missing(vma)) {
                *fault_type = handle_userfault(vmf, VM_UFFD_MISSING);
                return 0;
        }

        /* shmem_symlink() */
        if (mapping->a_ops != &shmem_aops)
                goto alloc_nohuge;
        if (shmem_huge == SHMEM_HUGE_DENY || sgp_huge == SGP_NOHUGE)
                goto alloc_nohuge;
        if (shmem_huge == SHMEM_HUGE_FORCE)
                goto alloc_huge;
        switch (sbinfo->huge) {
                loff_t i_size;
                pgoff_t off;
        case SHMEM_HUGE_NEVER:
                goto alloc_nohuge;
        case SHMEM_HUGE_WITHIN_SIZE:
                off = round_up(index, HPAGE_PMD_NR);
                i_size = round_up(i_size_read(inode), PAGE_SIZE);
                if (i_size >= HPAGE_PMD_SIZE &&
                    i_size >> PAGE_SHIFT >= off)
                        goto alloc_huge;
                /* fallthrough */
        case SHMEM_HUGE_ADVISE:
                if (sgp_huge == SGP_HUGE)
                        goto alloc_huge;
                /* TODO: implement fadvise() hints */
                goto alloc_nohuge;
        }

alloc_huge:
        page = shmem_alloc_and_acct_page(gfp, inode, index, true);
        if (IS_ERR(page)) {
alloc_nohuge:
                page = shmem_alloc_and_acct_page(gfp, inode,
                                                 index, false);
        }
        if (IS_ERR(page)) {
                int retry = 5;

                error = PTR_ERR(page);
                page = NULL;
                if (error != -ENOSPC)
                        goto unlock;
                /*
                 * Try to reclaim some space by splitting a huge page
                 * beyond i_size on the filesystem.
                 */
                while (retry--) {
                        int ret;

                        ret = shmem_unused_huge_shrink(sbinfo, NULL, 1);
                        if (ret == SHRINK_STOP)
                                break;
                        if (ret)
                                goto alloc_nohuge;
                }
                goto unlock;
        }

        if (PageTransHuge(page))
                hindex = round_down(index, HPAGE_PMD_NR);
        else
                hindex = index;

        if (sgp == SGP_WRITE)
                __SetPageReferenced(page);

        error = mem_cgroup_try_charge_delay(page, charge_mm, gfp, &memcg,
                                            PageTransHuge(page));
        if (error)
                goto unacct;
        error = shmem_add_to_page_cache(page, mapping, hindex,
                                        NULL, gfp & GFP_RECLAIM_MASK);
        if (error) {
                mem_cgroup_cancel_charge(page, memcg,
                                         PageTransHuge(page));
                goto unacct;
        }
        mem_cgroup_commit_charge(page, memcg, false,
                                 PageTransHuge(page));
        lru_cache_add_anon(page);

        spin_lock_irq(&info->lock);
        info->alloced += 1 << compound_order(page);
        inode->i_blocks += BLOCKS_PER_PAGE << compound_order(page);
        shmem_recalc_inode(inode);
        spin_unlock_irq(&info->lock);
        alloced = true;

        if (PageTransHuge(page) &&
            DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE) <
                        hindex + HPAGE_PMD_NR - 1) {
                /*
                 * Part of the huge page is beyond i_size: subject
                 * to shrink under memory pressure.
                 */
                spin_lock(&sbinfo->shrinklist_lock);
                /*
                 * _careful to defend against unlocked access to
                 * ->shrink_list in shmem_unused_huge_shrink()
                 */
                if (list_empty_careful(&info->shrinklist)) {
                        list_add_tail(&info->shrinklist,
                                      &sbinfo->shrinklist);
                        sbinfo->shrinklist_len++;
                }
                spin_unlock(&sbinfo->shrinklist_lock);
        }

        /*
         * Let SGP_FALLOC use the SGP_WRITE optimization on a new page.
         */
        if (sgp == SGP_FALLOC)
                sgp = SGP_WRITE;
clear:
        /*
         * Let SGP_WRITE caller clear ends if write does not fill page;
         * but SGP_FALLOC on a page fallocated earlier must initialize
         * it now, lest undo on failure cancel our earlier guarantee.
         */
        if (sgp != SGP_WRITE && !PageUptodate(page)) {
                struct page *head = compound_head(page);
                int i;

                for (i = 0; i < (1 << compound_order(head)); i++) {
                        clear_highpage(head + i);
                        flush_dcache_page(head + i);
                }
                SetPageUptodate(head);
        }

        /* Perhaps the file has been truncated since we checked */
        if (sgp <= SGP_CACHE &&
            ((loff_t)index << PAGE_SHIFT) >= i_size_read(inode)) {
                if (alloced) {
                        ClearPageDirty(page);
                        delete_from_page_cache(page);
                        spin_lock_irq(&info->lock);
                        shmem_recalc_inode(inode);
                        spin_unlock_irq(&info->lock);
                }
                error = -EINVAL;
                goto unlock;
        }
        *pagep = page + index - hindex;
        return 0;

        /*
         * Error recovery.
         */
unacct:
        shmem_inode_unacct_blocks(inode, 1 << compound_order(page));

        if (PageTransHuge(page)) {
                unlock_page(page);
                put_page(page);
                goto alloc_nohuge;
        }
unlock:
        if (page) {
                unlock_page(page);
                put_page(page);
        }
        if (error == -ENOSPC && !once++) {
                spin_lock_irq(&info->lock);
                shmem_recalc_inode(inode);
                spin_unlock_irq(&info->lock);
                goto repeat;
        }
        if (error == -EEXIST)
                goto repeat;
        return error;
}

/*
 * This is like autoremove_wake_function, but it removes the wait queue
 * entry unconditionally - even if something else had already woken the
 * target.
 */
static int synchronous_wake_function(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
{
        int ret = default_wake_function(wait, mode, sync, key);
        list_del_init(&wait->entry);
        return ret;
}

static vm_fault_t shmem_fault(struct vm_fault *vmf)
{
        struct vm_area_struct *vma = vmf->vma;
        struct inode *inode = file_inode(vma->vm_file);
        gfp_t gfp = mapping_gfp_mask(inode->i_mapping);
        enum sgp_type sgp;
        int err;
        vm_fault_t ret = VM_FAULT_LOCKED;

        /*
         * Trinity finds that probing a hole which tmpfs is punching can
         * prevent the hole-punch from ever completing: which in turn
         * locks writers out with its hold on i_mutex.  So refrain from
         * faulting pages into the hole while it's being punched.  Although
         * shmem_undo_range() does remove the additions, it may be unable to
         * keep up, as each new page needs its own unmap_mapping_range() call,
         * and the i_mmap tree grows ever slower to scan if new vmas are added.
         *
         * It does not matter if we sometimes reach this check just before the
         * hole-punch begins, so that one fault then races with the punch:
         * we just need to make racing faults a rare case.
         *
         * The implementation below would be much simpler if we just used a
         * standard mutex or completion: but we cannot take i_mutex in fault,
         * and bloating every shmem inode for this unlikely case would be sad.
         */
        if (unlikely(inode->i_private)) {
                struct shmem_falloc *shmem_falloc;

                spin_lock(&inode->i_lock);
                shmem_falloc = inode->i_private;
                if (shmem_falloc &&
                    shmem_falloc->waitq &&
                    vmf->pgoff >= shmem_falloc->start &&
                    vmf->pgoff < shmem_falloc->next) {
                        wait_queue_head_t *shmem_falloc_waitq;
                        DEFINE_WAIT_FUNC(shmem_fault_wait, synchronous_wake_function);

                        ret = VM_FAULT_NOPAGE;
                        if ((vmf->flags & FAULT_FLAG_ALLOW_RETRY) &&
                           !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
                                /* It's polite to up mmap_sem if we can */
                                up_read(&vma->vm_mm->mmap_sem);
                                ret = VM_FAULT_RETRY;
                        }

                        shmem_falloc_waitq = shmem_falloc->waitq;
                        prepare_to_wait(shmem_falloc_waitq, &shmem_fault_wait,
                                        TASK_UNINTERRUPTIBLE);
                        spin_unlock(&inode->i_lock);
                        schedule();

                        /*
                         * shmem_falloc_waitq points into the shmem_fallocate()
                         * stack of the hole-punching task: shmem_falloc_waitq
                         * is usually invalid by the time we reach here, but
                         * finish_wait() does not dereference it in that case;
                         * though i_lock needed lest racing with wake_up_all().
                         */
                        spin_lock(&inode->i_lock);
                        finish_wait(shmem_falloc_waitq, &shmem_fault_wait);
                        spin_unlock(&inode->i_lock);
                        return ret;
                }
                spin_unlock(&inode->i_lock);
        }

        sgp = SGP_CACHE;

        if ((vma->vm_flags & VM_NOHUGEPAGE) ||
            test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
                sgp = SGP_NOHUGE;
        else if (vma->vm_flags & VM_HUGEPAGE)
                sgp = SGP_HUGE;

        err = shmem_getpage_gfp(inode, vmf->pgoff, &vmf->page, sgp,
                                  gfp, vma, vmf, &ret);
        if (err)
                return vmf_error(err);
        return ret;
}

unsigned long shmem_get_unmapped_area(struct file *file,
                                      unsigned long uaddr, unsigned long len,
                                      unsigned long pgoff, unsigned long flags)
{
        unsigned long (*get_area)(struct file *,
                unsigned long, unsigned long, unsigned long, unsigned long);
        unsigned long addr;
        unsigned long offset;
        unsigned long inflated_len;
        unsigned long inflated_addr;
        unsigned long inflated_offset;

        if (len > TASK_SIZE)
                return -ENOMEM;

        get_area = current->mm->get_unmapped_area;
        addr = get_area(file, uaddr, len, pgoff, flags);

        if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE))
                return addr;
        if (IS_ERR_VALUE(addr))
                return addr;
        if (addr & ~PAGE_MASK)
                return addr;
        if (addr > TASK_SIZE - len)
                return addr;

        if (shmem_huge == SHMEM_HUGE_DENY)
                return addr;
        if (len < HPAGE_PMD_SIZE)
                return addr;
        if (flags & MAP_FIXED)
                return addr;
        /*
         * Our priority is to support MAP_SHARED mapped hugely;
         * and support MAP_PRIVATE mapped hugely too, until it is COWed.
         * But if caller specified an address hint, respect that as before.
         */
        if (uaddr)
                return addr;

        if (shmem_huge != SHMEM_HUGE_FORCE) {
                struct super_block *sb;

                if (file) {
                        VM_BUG_ON(file->f_op != &shmem_file_operations);
                        sb = file_inode(file)->i_sb;
                } else {
                        /*
                         * Called directly from mm/mmap.c, or drivers/char/mem.c
                         * for "/dev/zero", to create a shared anonymous object.
                         */
                        if (IS_ERR(shm_mnt))
                                return addr;
                        sb = shm_mnt->mnt_sb;
                }
                if (SHMEM_SB(sb)->huge == SHMEM_HUGE_NEVER)
                        return addr;
        }

        offset = (pgoff << PAGE_SHIFT) & (HPAGE_PMD_SIZE-1);
        if (offset && offset + len < 2 * HPAGE_PMD_SIZE)
                return addr;
        if ((addr & (HPAGE_PMD_SIZE-1)) == offset)
                return addr;

        inflated_len = len + HPAGE_PMD_SIZE - PAGE_SIZE;
        if (inflated_len > TASK_SIZE)
                return addr;
        if (inflated_len < len)
                return addr;

        inflated_addr = get_area(NULL, 0, inflated_len, 0, flags);
        if (IS_ERR_VALUE(inflated_addr))
                return addr;
        if (inflated_addr & ~PAGE_MASK)
                return addr;

        inflated_offset = inflated_addr & (HPAGE_PMD_SIZE-1);
        inflated_addr += offset - inflated_offset;
        if (inflated_offset > offset)
                inflated_addr += HPAGE_PMD_SIZE;

        if (inflated_addr > TASK_SIZE - len)
                return addr;
        return inflated_addr;
}

#ifdef CONFIG_NUMA
static int shmem_set_policy(struct vm_area_struct *vma, struct mempolicy *mpol)
{
        struct inode *inode = file_inode(vma->vm_file);
        return mpol_set_shared_policy(&SHMEM_I(inode)->policy, vma, mpol);
}

static struct mempolicy *shmem_get_policy(struct vm_area_struct *vma,
                                          unsigned long addr)
{
        struct inode *inode = file_inode(vma->vm_file);
        pgoff_t index;

        index = ((addr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
        return mpol_shared_policy_lookup(&SHMEM_I(inode)->policy, index);
}
#endif

int shmem_lock(struct file *file, int lock, struct user_struct *user)
{
        struct inode *inode = file_inode(file);
        struct shmem_inode_info *info = SHMEM_I(inode);
        int retval = -ENOMEM;

        spin_lock_irq(&info->lock);
        if (lock && !(info->flags & VM_LOCKED)) {
                if (!user_shm_lock(inode->i_size, user))
                        goto out_nomem;
                info->flags |= VM_LOCKED;
                mapping_set_unevictable(file->f_mapping);
        }
        if (!lock && (info->flags & VM_LOCKED) && user) {
                user_shm_unlock(inode->i_size, user);
                info->flags &= ~VM_LOCKED;
                mapping_clear_unevictable(file->f_mapping);
        }
        retval = 0;

out_nomem:
        spin_unlock_irq(&info->lock);
        return retval;
}

static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
{
        struct shmem_inode_info *info = SHMEM_I(file_inode(file));

        if (info->seals & F_SEAL_FUTURE_WRITE) {
                /*
                 * New PROT_WRITE and MAP_SHARED mmaps are not allowed when
                 * "future write" seal active.
                 */
                if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE))
                        return -EPERM;

                /*
                 * Since the F_SEAL_FUTURE_WRITE seals allow for a MAP_SHARED
                 * read-only mapping, take care to not allow mprotect to revert
                 * protections.
                 */
                vma->vm_flags &= ~(VM_MAYWRITE);
        }

        file_accessed(file);
        vma->vm_ops = &shmem_vm_ops;
        if (IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE) &&
                        ((vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK) <
                        (vma->vm_end & HPAGE_PMD_MASK)) {
                khugepaged_enter(vma, vma->vm_flags);
        }
        return 0;
}

static struct inode *shmem_get_inode(struct super_block *sb, const struct inode *dir,
                                     umode_t mode, dev_t dev, unsigned long flags)
{
        struct inode *inode;
        struct shmem_inode_info *info;
        struct shmem_sb_info *sbinfo = SHMEM_SB(sb);

        if (shmem_reserve_inode(sb))
                return NULL;

        inode = new_inode(sb);
        if (inode) {
                inode->i_ino = get_next_ino();
                inode_init_owner(inode, dir, mode);
                inode->i_blocks = 0;
                inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
                inode->i_generation = prandom_u32();
                info = SHMEM_I(inode);
                memset(info, 0, (char *)inode - (char *)info);
                spin_lock_init(&info->lock);
                atomic_set(&info->stop_eviction, 0);
                info->seals = F_SEAL_SEAL;
                info->flags = flags & VM_NORESERVE;
                INIT_LIST_HEAD(&info->shrinklist);
                INIT_LIST_HEAD(&info->swaplist);
                simple_xattrs_init(&info->xattrs);
                cache_no_acl(inode);

                switch (mode & S_IFMT) {
                default:
                        inode->i_op = &shmem_special_inode_operations;
                        init_special_inode(inode, mode, dev);
                        break;
                case S_IFREG:
                        inode->i_mapping->a_ops = &shmem_aops;
                        inode->i_op = &shmem_inode_operations;
                        inode->i_fop = &shmem_file_operations;
                        mpol_shared_policy_init(&info->policy,
                                                 shmem_get_sbmpol(sbinfo));
                        break;
                case S_IFDIR:
                        inc_nlink(inode);
                        /* Some things misbehave if size == 0 on a directory */
                        inode->i_size = 2 * BOGO_DIRENT_SIZE;
                        inode->i_op = &shmem_dir_inode_operations;
                        inode->i_fop = &simple_dir_operations;
                        break;
                case S_IFLNK:
                        /*
                         * Must not load anything in the rbtree,
                         * mpol_free_shared_policy will not be called.
                         */
                        mpol_shared_policy_init(&info->policy, NULL);
                        break;
                }

                lockdep_annotate_inode_mutex_key(inode);
        } else
                shmem_free_inode(sb);
        return inode;
}

bool shmem_mapping(struct address_space *mapping)
{
        return mapping->a_ops == &shmem_aops;
}

static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm,
                                  pmd_t *dst_pmd,
                                  struct vm_area_struct *dst_vma,
                                  unsigned long dst_addr,
                                  unsigned long src_addr,
                                  bool zeropage,
                                  struct page **pagep)
{
        struct inode *inode = file_inode(dst_vma->vm_file);
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct address_space *mapping = inode->i_mapping;
        gfp_t gfp = mapping_gfp_mask(mapping);
        pgoff_t pgoff = linear_page_index(dst_vma, dst_addr);
        struct mem_cgroup *memcg;
        spinlock_t *ptl;
        void *page_kaddr;
        struct page *page;
        pte_t _dst_pte, *dst_pte;
        int ret;
        pgoff_t offset, max_off;

        ret = -ENOMEM;
        if (!shmem_inode_acct_block(inode, 1))
                goto out;

        if (!*pagep) {
                page = shmem_alloc_page(gfp, info, pgoff);
                if (!page)
                        goto out_unacct_blocks;

                if (!zeropage) {        /* mcopy_atomic */
                        page_kaddr = kmap_atomic(page);
                        ret = copy_from_user(page_kaddr,
                                             (const void __user *)src_addr,
                                             PAGE_SIZE);
                        kunmap_atomic(page_kaddr);

                        /* fallback to copy_from_user outside mmap_sem */
                        if (unlikely(ret)) {
                                *pagep = page;
                                shmem_inode_unacct_blocks(inode, 1);
                                /* don't free the page */
                                return -ENOENT;
                        }
                } else {                /* mfill_zeropage_atomic */
                        clear_highpage(page);
                }
        } else {
                page = *pagep;
                *pagep = NULL;
        }

        VM_BUG_ON(PageLocked(page) || PageSwapBacked(page));
        __SetPageLocked(page);
        __SetPageSwapBacked(page);
        __SetPageUptodate(page);

        ret = -EFAULT;
        offset = linear_page_index(dst_vma, dst_addr);
        max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
        if (unlikely(offset >= max_off))
                goto out_release;

        ret = mem_cgroup_try_charge_delay(page, dst_mm, gfp, &memcg, false);
        if (ret)
                goto out_release;

        ret = shmem_add_to_page_cache(page, mapping, pgoff, NULL,
                                                gfp & GFP_RECLAIM_MASK);
        if (ret)
                goto out_release_uncharge;

        mem_cgroup_commit_charge(page, memcg, false, false);

        _dst_pte = mk_pte(page, dst_vma->vm_page_prot);
        if (dst_vma->vm_flags & VM_WRITE)
                _dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte));
        else {
                /*
                 * We don't set the pte dirty if the vma has no
                 * VM_WRITE permission, so mark the page dirty or it
                 * could be freed from under us. We could do it
                 * unconditionally before unlock_page(), but doing it
                 * only if VM_WRITE is not set is faster.
                 */
                set_page_dirty(page);
        }

        dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);

        ret = -EFAULT;
        max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
        if (unlikely(offset >= max_off))
                goto out_release_uncharge_unlock;

        ret = -EEXIST;
        if (!pte_none(*dst_pte))
                goto out_release_uncharge_unlock;

        lru_cache_add_anon(page);

        spin_lock(&info->lock);
        info->alloced++;
        inode->i_blocks += BLOCKS_PER_PAGE;
        shmem_recalc_inode(inode);
        spin_unlock(&info->lock);

        inc_mm_counter(dst_mm, mm_counter_file(page));
        page_add_file_rmap(page, false);
        set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);

        /* No need to invalidate - it was non-present before */
        update_mmu_cache(dst_vma, dst_addr, dst_pte);
        pte_unmap_unlock(dst_pte, ptl);
        unlock_page(page);
        ret = 0;
out:
        return ret;
out_release_uncharge_unlock:
        pte_unmap_unlock(dst_pte, ptl);
        ClearPageDirty(page);
        delete_from_page_cache(page);
out_release_uncharge:
        mem_cgroup_cancel_charge(page, memcg, false);
out_release:
        unlock_page(page);
        put_page(page);
out_unacct_blocks:
        shmem_inode_unacct_blocks(inode, 1);
        goto out;
}

int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm,
                           pmd_t *dst_pmd,
                           struct vm_area_struct *dst_vma,
                           unsigned long dst_addr,
                           unsigned long src_addr,
                           struct page **pagep)
{
        return shmem_mfill_atomic_pte(dst_mm, dst_pmd, dst_vma,
                                      dst_addr, src_addr, false, pagep);
}

int shmem_mfill_zeropage_pte(struct mm_struct *dst_mm,
                             pmd_t *dst_pmd,
                             struct vm_area_struct *dst_vma,
                             unsigned long dst_addr)
{
        struct page *page = NULL;

        return shmem_mfill_atomic_pte(dst_mm, dst_pmd, dst_vma,
                                      dst_addr, 0, true, &page);
}

#ifdef CONFIG_TMPFS
static const struct inode_operations shmem_symlink_inode_operations;
static const struct inode_operations shmem_short_symlink_operations;

#ifdef CONFIG_TMPFS_XATTR
static int shmem_initxattrs(struct inode *, const struct xattr *, void *);
#else
#define shmem_initxattrs NULL
#endif

static int
shmem_write_begin(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned flags,
                        struct page **pagep, void **fsdata)
{
        struct inode *inode = mapping->host;
        struct shmem_inode_info *info = SHMEM_I(inode);
        pgoff_t index = pos >> PAGE_SHIFT;

        /* i_mutex is held by caller */
        if (unlikely(info->seals & (F_SEAL_GROW |
                                   F_SEAL_WRITE | F_SEAL_FUTURE_WRITE))) {
                if (info->seals & (F_SEAL_WRITE | F_SEAL_FUTURE_WRITE))
                        return -EPERM;
                if ((info->seals & F_SEAL_GROW) && pos + len > inode->i_size)
                        return -EPERM;
        }

        return shmem_getpage(inode, index, pagep, SGP_WRITE);
}

static int
shmem_write_end(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned copied,
                        struct page *page, void *fsdata)
{
        struct inode *inode = mapping->host;

        if (pos + copied > inode->i_size)
                i_size_write(inode, pos + copied);

        if (!PageUptodate(page)) {
                struct page *head = compound_head(page);
                if (PageTransCompound(page)) {
                        int i;

                        for (i = 0; i < HPAGE_PMD_NR; i++) {
                                if (head + i == page)
                                        continue;
                                clear_highpage(head + i);
                                flush_dcache_page(head + i);
                        }
                }
                if (copied < PAGE_SIZE) {
                        unsigned from = pos & (PAGE_SIZE - 1);
                        zero_user_segments(page, 0, from,
                                        from + copied, PAGE_SIZE);
                }
                SetPageUptodate(head);
        }
        set_page_dirty(page);
        unlock_page(page);
        put_page(page);

        return copied;
}

static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file_inode(file);
        struct address_space *mapping = inode->i_mapping;
        pgoff_t index;
        unsigned long offset;
        enum sgp_type sgp = SGP_READ;
        int error = 0;
        ssize_t retval = 0;
        loff_t *ppos = &iocb->ki_pos;

        /*
         * Might this read be for a stacking filesystem?  Then when reading
         * holes of a sparse file, we actually need to allocate those pages,
         * and even mark them dirty, so it cannot exceed the max_blocks limit.
         */
        if (!iter_is_iovec(to))
                sgp = SGP_CACHE;

        index = *ppos >> PAGE_SHIFT;
        offset = *ppos & ~PAGE_MASK;

        for (;;) {
                struct page *page = NULL;
                pgoff_t end_index;
                unsigned long nr, ret;
                loff_t i_size = i_size_read(inode);

                end_index = i_size >> PAGE_SHIFT;
                if (index > end_index)
                        break;
                if (index == end_index) {
                        nr = i_size & ~PAGE_MASK;
                        if (nr <= offset)
                                break;
                }

                error = shmem_getpage(inode, index, &page, sgp);
                if (error) {
                        if (error == -EINVAL)
                                error = 0;
                        break;
                }
                if (page) {
                        if (sgp == SGP_CACHE)
                                set_page_dirty(page);
                        unlock_page(page);
                }

                /*
                 * We must evaluate after, since reads (unlike writes)
                 * are called without i_mutex protection against truncate
                 */
                nr = PAGE_SIZE;
                i_size = i_size_read(inode);
                end_index = i_size >> PAGE_SHIFT;
                if (index == end_index) {
                        nr = i_size & ~PAGE_MASK;
                        if (nr <= offset) {
                                if (page)
                                        put_page(page);
                                break;
                        }
                }
                nr -= offset;

                if (page) {
                        /*
                         * If users can be writing to this page using arbitrary
                         * virtual addresses, take care about potential aliasing
                         * before reading the page on the kernel side.
                         */
                        if (mapping_writably_mapped(mapping))
                                flush_dcache_page(page);
                        /*
                         * Mark the page accessed if we read the beginning.
                         */
                        if (!offset)
                                mark_page_accessed(page);
                } else {
                        page = ZERO_PAGE(0);
                        get_page(page);
                }

                /*
                 * Ok, we have the page, and it's up-to-date, so
                 * now we can copy it to user space...
                 */
                ret = copy_page_to_iter(page, offset, nr, to);
                retval += ret;
                offset += ret;
                index += offset >> PAGE_SHIFT;
                offset &= ~PAGE_MASK;

                put_page(page);
                if (!iov_iter_count(to))
                        break;
                if (ret < nr) {
                        error = -EFAULT;
                        break;
                }
                cond_resched();
        }

        *ppos = ((loff_t) index << PAGE_SHIFT) + offset;
        file_accessed(file);
        return retval ? retval : error;
}

/*
 * llseek SEEK_DATA or SEEK_HOLE through the page cache.
 */
static pgoff_t shmem_seek_hole_data(struct address_space *mapping,
                                    pgoff_t index, pgoff_t end, int whence)
{
        struct page *page;
        struct pagevec pvec;
        pgoff_t indices[PAGEVEC_SIZE];
        bool done = false;
        int i;

        pagevec_init(&pvec);
        pvec.nr = 1;            /* start small: we may be there already */
        while (!done) {
                pvec.nr = find_get_entries(mapping, index,
                                        pvec.nr, pvec.pages, indices);
                if (!pvec.nr) {
                        if (whence == SEEK_DATA)
                                index = end;
                        break;
                }
                for (i = 0; i < pvec.nr; i++, index++) {
                        if (index < indices[i]) {
                                if (whence == SEEK_HOLE) {
                                        done = true;
                                        break;
                                }
                                index = indices[i];
                        }
                        page = pvec.pages[i];
                        if (page && !xa_is_value(page)) {
                                if (!PageUptodate(page))
                                        page = NULL;
                        }
                        if (index >= end ||
                            (page && whence == SEEK_DATA) ||
                            (!page && whence == SEEK_HOLE)) {
                                done = true;
                                break;
                        }
                }
                pagevec_remove_exceptionals(&pvec);
                pagevec_release(&pvec);
                pvec.nr = PAGEVEC_SIZE;
                cond_resched();
        }
        return index;
}

static loff_t shmem_file_llseek(struct file *file, loff_t offset, int whence)
{
        struct address_space *mapping = file->f_mapping;
        struct inode *inode = mapping->host;
        pgoff_t start, end;
        loff_t new_offset;

        if (whence != SEEK_DATA && whence != SEEK_HOLE)
                return generic_file_llseek_size(file, offset, whence,
                                        MAX_LFS_FILESIZE, i_size_read(inode));
        inode_lock(inode);
        /* We're holding i_mutex so we can access i_size directly */

        if (offset < 0 || offset >= inode->i_size)
                offset = -ENXIO;
        else {
                start = offset >> PAGE_SHIFT;
                end = (inode->i_size + PAGE_SIZE - 1) >> PAGE_SHIFT;
                new_offset = shmem_seek_hole_data(mapping, start, end, whence);
                new_offset <<= PAGE_SHIFT;
                if (new_offset > offset) {
                        if (new_offset < inode->i_size)
                                offset = new_offset;
                        else if (whence == SEEK_DATA)
                                offset = -ENXIO;
                        else
                                offset = inode->i_size;
                }
        }

        if (offset >= 0)
                offset = vfs_setpos(file, offset, MAX_LFS_FILESIZE);
        inode_unlock(inode);
        return offset;
}

static long shmem_fallocate(struct file *file, int mode, loff_t offset,
                                                         loff_t len)
{
        struct inode *inode = file_inode(file);
        struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct shmem_falloc shmem_falloc;
        pgoff_t start, index, end;
        int error;

        if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
                return -EOPNOTSUPP;

        inode_lock(inode);

        if (mode & FALLOC_FL_PUNCH_HOLE) {
                struct address_space *mapping = file->f_mapping;
                loff_t unmap_start = round_up(offset, PAGE_SIZE);
                loff_t unmap_end = round_down(offset + len, PAGE_SIZE) - 1;
                DECLARE_WAIT_QUEUE_HEAD_ONSTACK(shmem_falloc_waitq);

                /* protected by i_mutex */
                if (info->seals & (F_SEAL_WRITE | F_SEAL_FUTURE_WRITE)) {
                        error = -EPERM;
                        goto out;
                }

                shmem_falloc.waitq = &shmem_falloc_waitq;
                shmem_falloc.start = unmap_start >> PAGE_SHIFT;
                shmem_falloc.next = (unmap_end + 1) >> PAGE_SHIFT;
                spin_lock(&inode->i_lock);
                inode->i_private = &shmem_falloc;
                spin_unlock(&inode->i_lock);

                if ((u64)unmap_end > (u64)unmap_start)
                        unmap_mapping_range(mapping, unmap_start,
                                            1 + unmap_end - unmap_start, 0);
                shmem_truncate_range(inode, offset, offset + len - 1);
                /* No need to unmap again: hole-punching leaves COWed pages */

                spin_lock(&inode->i_lock);
                inode->i_private = NULL;
                wake_up_all(&shmem_falloc_waitq);
                WARN_ON_ONCE(!list_empty(&shmem_falloc_waitq.head));
                spin_unlock(&inode->i_lock);
                error = 0;
                goto out;
        }

        /* We need to check rlimit even when FALLOC_FL_KEEP_SIZE */
        error = inode_newsize_ok(inode, offset + len);
        if (error)
                goto out;

        if ((info->seals & F_SEAL_GROW) && offset + len > inode->i_size) {
                error = -EPERM;
                goto out;
        }

        start = offset >> PAGE_SHIFT;
        end = (offset + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
        /* Try to avoid a swapstorm if len is impossible to satisfy */
        if (sbinfo->max_blocks && end - start > sbinfo->max_blocks) {
                error = -ENOSPC;
                goto out;
        }

        shmem_falloc.waitq = NULL;
        shmem_falloc.start = start;
        shmem_falloc.next  = start;
        shmem_falloc.nr_falloced = 0;
        shmem_falloc.nr_unswapped = 0;
        spin_lock(&inode->i_lock);
        inode->i_private = &shmem_falloc;
        spin_unlock(&inode->i_lock);

        for (index = start; index < end; index++) {
                struct page *page;

                /*
                 * Good, the fallocate(2) manpage permits EINTR: we may have
                 * been interrupted because we are using up too much memory.
                 */
                if (signal_pending(current))
                        error = -EINTR;
                else if (shmem_falloc.nr_unswapped > shmem_falloc.nr_falloced)
                        error = -ENOMEM;
                else
                        error = shmem_getpage(inode, index, &page, SGP_FALLOC);
                if (error) {
                        /* Remove the !PageUptodate pages we added */
                        if (index > start) {
                                shmem_undo_range(inode,
                                    (loff_t)start << PAGE_SHIFT,
                                    ((loff_t)index << PAGE_SHIFT) - 1, true);
                        }
                        goto undone;
                }

                /*
                 * Inform shmem_writepage() how far we have reached.
                 * No need for lock or barrier: we have the page lock.
                 */
                shmem_falloc.next++;
                if (!PageUptodate(page))
                        shmem_falloc.nr_falloced++;

                /*
                 * If !PageUptodate, leave it that way so that freeable pages
                 * can be recognized if we need to rollback on error later.
                 * But set_page_dirty so that memory pressure will swap rather
                 * than free the pages we are allocating (and SGP_CACHE pages
                 * might still be clean: we now need to mark those dirty too).
                 */
                set_page_dirty(page);
                unlock_page(page);
                put_page(page);
                cond_resched();
        }

        if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size)
                i_size_write(inode, offset + len);
        inode->i_ctime = current_time(inode);
undone:
        spin_lock(&inode->i_lock);
        inode->i_private = NULL;
        spin_unlock(&inode->i_lock);
out:
        inode_unlock(inode);
        return error;
}

static int shmem_statfs(struct dentry *dentry, struct kstatfs *buf)
{
        struct shmem_sb_info *sbinfo = SHMEM_SB(dentry->d_sb);

        buf->f_type = TMPFS_MAGIC;
        buf->f_bsize = PAGE_SIZE;
        buf->f_namelen = NAME_MAX;
        if (sbinfo->max_blocks) {
                buf->f_blocks = sbinfo->max_blocks;
                buf->f_bavail =
                buf->f_bfree  = sbinfo->max_blocks -
                                percpu_counter_sum(&sbinfo->used_blocks);
        }
        if (sbinfo->max_inodes) {
                buf->f_files = sbinfo->max_inodes;
                buf->f_ffree = sbinfo->free_inodes;
        }
        /* else leave those fields 0 like simple_statfs */
        return 0;
}

/*
 * File creation. Allocate an inode, and we're done..
 */
static int
shmem_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
{
        struct inode *inode;
        int error = -ENOSPC;

        inode = shmem_get_inode(dir->i_sb, dir, mode, dev, VM_NORESERVE);
        if (inode) {
                error = simple_acl_create(dir, inode);
                if (error)
                        goto out_iput;
                error = security_inode_init_security(inode, dir,
                                                     &dentry->d_name,
                                                     shmem_initxattrs, NULL);
                if (error && error != -EOPNOTSUPP)
                        goto out_iput;

                error = 0;
                dir->i_size += BOGO_DIRENT_SIZE;
                dir->i_ctime = dir->i_mtime = current_time(dir);
                d_instantiate(dentry, inode);
                dget(dentry); /* Extra count - pin the dentry in core */
        }
        return error;
out_iput:
        iput(inode);
        return error;
}

static int
shmem_tmpfile(struct inode *dir, struct dentry *dentry, umode_t mode)
{
        struct inode *inode;
        int error = -ENOSPC;

        inode = shmem_get_inode(dir->i_sb, dir, mode, 0, VM_NORESERVE);
        if (inode) {
                error = security_inode_init_security(inode, dir,
                                                     NULL,
                                                     shmem_initxattrs, NULL);
                if (error && error != -EOPNOTSUPP)
                        goto out_iput;
                error = simple_acl_create(dir, inode);
                if (error)
                        goto out_iput;
                d_tmpfile(dentry, inode);
        }
        return error;
out_iput:
        iput(inode);
        return error;
}

static int shmem_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
{
        int error;

        if ((error = shmem_mknod(dir, dentry, mode | S_IFDIR, 0)))
                return error;
        inc_nlink(dir);
        return 0;
}

static int shmem_create(struct inode *dir, struct dentry *dentry, umode_t mode,
                bool excl)
{
        return shmem_mknod(dir, dentry, mode | S_IFREG, 0);
}

/*
 * Link a file..
 */
static int shmem_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry)
{
        struct inode *inode = d_inode(old_dentry);
        int ret = 0;

        /*
         * No ordinary (disk based) filesystem counts links as inodes;
         * but each new link needs a new dentry, pinning lowmem, and
         * tmpfs dentries cannot be pruned until they are unlinked.
         * But if an O_TMPFILE file is linked into the tmpfs, the
         * first link must skip that, to get the accounting right.
         */
        if (inode->i_nlink) {
                ret = shmem_reserve_inode(inode->i_sb);
                if (ret)
                        goto out;
        }

        dir->i_size += BOGO_DIRENT_SIZE;
        inode->i_ctime = dir->i_ctime = dir->i_mtime = current_time(inode);
        inc_nlink(inode);
        ihold(inode);   /* New dentry reference */
        dget(dentry);           /* Extra pinning count for the created dentry */
        d_instantiate(dentry, inode);
out:
        return ret;
}

static int shmem_unlink(struct inode *dir, struct dentry *dentry)
{
        struct inode *inode = d_inode(dentry);

        if (inode->i_nlink > 1 && !S_ISDIR(inode->i_mode))
                shmem_free_inode(inode->i_sb);

        dir->i_size -= BOGO_DIRENT_SIZE;
        inode->i_ctime = dir->i_ctime = dir->i_mtime = current_time(inode);
        drop_nlink(inode);
        dput(dentry);   /* Undo the count from "create" - this does all the work */
        return 0;
}

static int shmem_rmdir(struct inode *dir, struct dentry *dentry)
{
        if (!simple_empty(dentry))
                return -ENOTEMPTY;

        drop_nlink(d_inode(dentry));
        drop_nlink(dir);
        return shmem_unlink(dir, dentry);
}

static int shmem_exchange(struct inode *old_dir, struct dentry *old_dentry, struct inode *new_dir, struct dentry *new_dentry)
{
        bool old_is_dir = d_is_dir(old_dentry);
        bool new_is_dir = d_is_dir(new_dentry);

        if (old_dir != new_dir && old_is_dir != new_is_dir) {
                if (old_is_dir) {
                        drop_nlink(old_dir);
                        inc_nlink(new_dir);
                } else {
                        drop_nlink(new_dir);
                        inc_nlink(old_dir);
                }
        }
        old_dir->i_ctime = old_dir->i_mtime =
        new_dir->i_ctime = new_dir->i_mtime =
        d_inode(old_dentry)->i_ctime =
        d_inode(new_dentry)->i_ctime = current_time(old_dir);

        return 0;
}