/*
 * SLUB: A slab allocator that limits cache line use instead of queuing
 * objects in per cpu and per node lists.
 *
 * The allocator synchronizes using per slab locks or atomic operatios
 * and only uses a centralized lock to manage a pool of partial slabs.
 *
 * (C) 2007 SGI, Christoph Lameter
 * (C) 2011 Linux Foundation, Christoph Lameter
 */

#include <linux/mm.h>
#include <linux/swap.h> /* struct reclaim_state */
#include <linux/module.h>
#include <linux/bit_spinlock.h>
#include <linux/interrupt.h>
#include <linux/bitops.h>
#include <linux/slab.h>
#include "slab.h"
#include <linux/proc_fs.h>
#include <linux/notifier.h>
#include <linux/seq_file.h>
#include <linux/kmemcheck.h>
#include <linux/cpu.h>
#include <linux/cpuset.h>
#include <linux/mempolicy.h>
#include <linux/ctype.h>
#include <linux/debugobjects.h>
#include <linux/kallsyms.h>
#include <linux/memory.h>
#include <linux/math64.h>
#include <linux/fault-inject.h>
#include <linux/stacktrace.h>
#include <linux/prefetch.h>
#include <linux/memcontrol.h>

#include <trace/events/kmem.h>

#include "internal.h"

/*
 * Lock order:
 *   1. slab_mutex (Global Mutex)
 *   2. node->list_lock
 *   3. slab_lock(page) (Only on some arches and for debugging)
 *
 *   slab_mutex
 *
 *   The role of the slab_mutex is to protect the list of all the slabs
 *   and to synchronize major metadata changes to slab cache structures.
 *
 *   The slab_lock is only used for debugging and on arches that do not
 *   have the ability to do a cmpxchg_double. It only protects the second
 *   double word in the page struct. Meaning
 *      A. page->freelist       -> List of object free in a page
 *      B. page->counters       -> Counters of objects
 *      C. page->frozen         -> frozen state
 *
 *   If a slab is frozen then it is exempt from list management. It is not
 *   on any list. The processor that froze the slab is the one who can
 *   perform list operations on the page. Other processors may put objects
 *   onto the freelist but the processor that froze the slab is the only
 *   one that can retrieve the objects from the page's freelist.
 *
 *   The list_lock protects the partial and full list on each node and
 *   the partial slab counter. If taken then no new slabs may be added or
 *   removed from the lists nor make the number of partial slabs be modified.
 *   (Note that the total number of slabs is an atomic value that may be
 *   modified without taking the list lock).
 *
 *   The list_lock is a centralized lock and thus we avoid taking it as
 *   much as possible. As long as SLUB does not have to handle partial
 *   slabs, operations can continue without any centralized lock. F.e.
 *   allocating a long series of objects that fill up slabs does not require
 *   the list lock.
 *   Interrupts are disabled during allocation and deallocation in order to
 *   make the slab allocator safe to use in the context of an irq. In addition
 *   interrupts are disabled to ensure that the processor does not change
 *   while handling per_cpu slabs, due to kernel preemption.
 *
 * SLUB assigns one slab for allocation to each processor.
 * Allocations only occur from these slabs called cpu slabs.
 *
 * Slabs with free elements are kept on a partial list and during regular
 * operations no list for full slabs is used. If an object in a full slab is
 * freed then the slab will show up again on the partial lists.
 * We track full slabs for debugging purposes though because otherwise we
 * cannot scan all objects.
 *
 * Slabs are freed when they become empty. Teardown and setup is
 * minimal so we rely on the page allocators per cpu caches for
 * fast frees and allocs.
 *
 * Overloading of page flags that are otherwise used for LRU management.
 *
 * PageActive           The slab is frozen and exempt from list processing.
 *                      This means that the slab is dedicated to a purpose
 *                      such as satisfying allocations for a specific
 *                      processor. Objects may be freed in the slab while
 *                      it is frozen but slab_free will then skip the usual
 *                      list operations. It is up to the processor holding
 *                      the slab to integrate the slab into the slab lists
 *                      when the slab is no longer needed.
 *
 *                      One use of this flag is to mark slabs that are
 *                      used for allocations. Then such a slab becomes a cpu
 *                      slab. The cpu slab may be equipped with an additional
 *                      freelist that allows lockless access to
 *                      free objects in addition to the regular freelist
 *                      that requires the slab lock.
 *
 * PageError            Slab requires special handling due to debug
 *                      options set. This moves slab handling out of
 *                      the fast path and disables lockless freelists.
 */

static inline int kmem_cache_debug(struct kmem_cache *s)
{
#ifdef CONFIG_SLUB_DEBUG
        return unlikely(s->flags & SLAB_DEBUG_FLAGS);
#else
        return 0;
#endif
}

static inline void *fixup_red_left(struct kmem_cache *s, void *p)
{
        if (kmem_cache_debug(s) && s->flags & SLAB_RED_ZONE)
                p += s->red_left_pad;

        return p;
}

/*
 * Issues still to be resolved:
 *
 * - Support PAGE_ALLOC_DEBUG. Should be easy to do.
 *
 * - Variable sizing of the per node arrays
 */

/* Enable to test recovery from slab corruption on boot */
#undef SLUB_RESILIENCY_TEST

/* Enable to log cmpxchg failures */
#undef SLUB_DEBUG_CMPXCHG

/*
 * Mininum number of partial slabs. These will be left on the partial
 * lists even if they are empty. kmem_cache_shrink may reclaim them.
 */
#define MIN_PARTIAL 5

/*
 * Maximum number of desirable partial slabs.
 * The existence of more partial slabs makes kmem_cache_shrink
 * sort the partial list by the number of objects in the.
 */
#define MAX_PARTIAL 10

#define DEBUG_DEFAULT_FLAGS (SLAB_CONSISTENCY_CHECKS | SLAB_RED_ZONE | \
                                SLAB_POISON | SLAB_STORE_USER)

/*
 * These debug flags cannot use CMPXCHG because there might be consistency
 * issues when checking or reading debug information
 */
#define SLAB_NO_CMPXCHG (SLAB_CONSISTENCY_CHECKS | SLAB_STORE_USER | \
                                SLAB_TRACE)


/*
 * Debugging flags that require metadata to be stored in the slab.  These get
 * disabled when slub_debug=O is used and a cache's min order increases with
 * metadata.
 */
#define DEBUG_METADATA_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER)

/*
 * Set of flags that will prevent slab merging
 */
#define SLUB_NEVER_MERGE (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \
                SLAB_TRACE | SLAB_DESTROY_BY_RCU | SLAB_NOLEAKTRACE | \
                SLAB_FAILSLAB)

#define SLUB_MERGE_SAME (SLAB_CONSISTENCY_CHECKS | SLAB_RECLAIM_ACCOUNT | \
                SLAB_CACHE_DMA | SLAB_NOTRACK | SLAB_ACCOUNT)

#define OO_SHIFT        16
#define OO_MASK         ((1 << OO_SHIFT) - 1)
#define MAX_OBJS_PER_PAGE       32767 /* since page.objects is u15 */

/* Internal SLUB flags */
#define __OBJECT_POISON         0x80000000UL /* Poison object */
#define __CMPXCHG_DOUBLE        0x40000000UL /* Use cmpxchg_double */

#ifdef CONFIG_SMP
static struct notifier_block slab_notifier;
#endif

/*
 * Tracking user of a slab.
 */
#define TRACK_ADDRS_COUNT 16
struct track {
        unsigned long addr;     /* Called from address */
#ifdef CONFIG_STACKTRACE
        unsigned long addrs[TRACK_ADDRS_COUNT]; /* Called from address */
#endif
        int cpu;                /* Was running on cpu */
        int pid;                /* Pid context */
        unsigned long when;     /* When did the operation occur */
};

enum track_item { TRACK_ALLOC, TRACK_FREE };

#ifdef CONFIG_SYSFS
static int sysfs_slab_add(struct kmem_cache *);
static int sysfs_slab_alias(struct kmem_cache *, const char *);
static void sysfs_slab_remove(struct kmem_cache *);
static void memcg_propagate_slab_attrs(struct kmem_cache *s);
#else
static inline int sysfs_slab_add(struct kmem_cache *s) { return 0; }
static inline int sysfs_slab_alias(struct kmem_cache *s, const char *p)
                                                        { return 0; }
static inline void sysfs_slab_remove(struct kmem_cache *s) { }

static inline void memcg_propagate_slab_attrs(struct kmem_cache *s) { }
#endif

static inline void stat(const struct kmem_cache *s, enum stat_item si)
{
#ifdef CONFIG_SLUB_STATS
        __this_cpu_inc(s->cpu_slab->stat[si]);
#endif
}

/********************************************************************
 *                      Core slab cache functions
 *******************************************************************/

static inline struct kmem_cache_node *get_node(struct kmem_cache *s, int node)
{
        return s->node[node];
}

static inline void *get_freepointer(struct kmem_cache *s, void *object)
{
        return *(void **)(object + s->offset);
}

static void prefetch_freepointer(const struct kmem_cache *s, void *object)
{
        prefetch(object + s->offset);
}

static inline void *get_freepointer_safe(struct kmem_cache *s, void *object)
{
        void *p;

        if (!debug_pagealloc_enabled())
                return get_freepointer(s, object);

        probe_kernel_read(&p, (void **)(object + s->offset), sizeof(p));
        return p;
}

static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp)
{
        *(void **)(object + s->offset) = fp;
}

/* Loop over all objects in a slab */
#define for_each_object(__p, __s, __addr, __objects) \
        for (__p = fixup_red_left(__s, __addr); \
                __p < (__addr) + (__objects) * (__s)->size; \
                __p += (__s)->size)

#define for_each_object_idx(__p, __idx, __s, __addr, __objects) \
        for (__p = fixup_red_left(__s, __addr), __idx = 1; \
                __idx <= __objects; \
                __p += (__s)->size, __idx++)

/* Determine object index from a given position */
static inline int slab_index(void *p, struct kmem_cache *s, void *addr)
{
        return (p - addr) / s->size;
}

static inline size_t slab_ksize(const struct kmem_cache *s)
{
#ifdef CONFIG_SLUB_DEBUG
        /*
         * Debugging requires use of the padding between object
         * and whatever may come after it.
         */
        if (s->flags & (SLAB_RED_ZONE | SLAB_POISON))
                return s->object_size;

#endif
        /*
         * If we have the need to store the freelist pointer
         * back there or track user information then we can
         * only use the space before that information.
         */
        if (s->flags & (SLAB_DESTROY_BY_RCU | SLAB_STORE_USER))
                return s->inuse;
        /*
         * Else we can use all the padding etc for the allocation
         */
        return s->size;
}

static inline int order_objects(int order, unsigned long size, int reserved)
{
        return ((PAGE_SIZE << order) - reserved) / size;
}

static inline struct kmem_cache_order_objects oo_make(int order,
                unsigned long size, int reserved)
{
        struct kmem_cache_order_objects x = {
                (order << OO_SHIFT) + order_objects(order, size, reserved)
        };

        return x;
}

static inline int oo_order(struct kmem_cache_order_objects x)
{
        return x.x >> OO_SHIFT;
}

static inline int oo_objects(struct kmem_cache_order_objects x)
{
        return x.x & OO_MASK;
}

/*
 * Per slab locking using the pagelock
 */
static __always_inline void slab_lock(struct page *page)
{
        bit_spin_lock(PG_locked, &page->flags);
}

static __always_inline void slab_unlock(struct page *page)
{
        __bit_spin_unlock(PG_locked, &page->flags);
}

static inline void set_page_slub_counters(struct page *page, unsigned long counters_new)
{
        struct page tmp;
        tmp.counters = counters_new;
        /*
         * page->counters can cover frozen/inuse/objects as well
         * as page->_count.  If we assign to ->counters directly
         * we run the risk of losing updates to page->_count, so
         * be careful and only assign to the fields we need.
         */
        page->frozen  = tmp.frozen;
        page->inuse   = tmp.inuse;
        page->objects = tmp.objects;
}

/* Interrupts must be disabled (for the fallback code to work right) */
static inline bool __cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
                void *freelist_old, unsigned long counters_old,
                void *freelist_new, unsigned long counters_new,
                const char *n)
{
        VM_BUG_ON(!irqs_disabled());
#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \
    defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
        if (s->flags & __CMPXCHG_DOUBLE) {
                if (cmpxchg_double(&page->freelist, &page->counters,
                        freelist_old, counters_old,
                        freelist_new, counters_new))
                return 1;
        } else
#endif
        {
                slab_lock(page);
                if (page->freelist == freelist_old && page->counters == counters_old) {
                        page->freelist = freelist_new;
                        set_page_slub_counters(page, counters_new);
                        slab_unlock(page);
                        return 1;
                }
                slab_unlock(page);
        }

        cpu_relax();
        stat(s, CMPXCHG_DOUBLE_FAIL);

#ifdef SLUB_DEBUG_CMPXCHG
        printk(KERN_INFO "%s %s: cmpxchg double redo ", n, s->name);
#endif

        return 0;
}

static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
                void *freelist_old, unsigned long counters_old,
                void *freelist_new, unsigned long counters_new,
                const char *n)
{
#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \
    defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
        if (s->flags & __CMPXCHG_DOUBLE) {
                if (cmpxchg_double(&page->freelist, &page->counters,
                        freelist_old, counters_old,
                        freelist_new, counters_new))
                return 1;
        } else
#endif
        {
                unsigned long flags;

                local_irq_save(flags);
                slab_lock(page);
                if (page->freelist == freelist_old && page->counters == counters_old) {
                        page->freelist = freelist_new;
                        set_page_slub_counters(page, counters_new);
                        slab_unlock(page);
                        local_irq_restore(flags);
                        return 1;
                }
                slab_unlock(page);
                local_irq_restore(flags);
        }

        cpu_relax();
        stat(s, CMPXCHG_DOUBLE_FAIL);

#ifdef SLUB_DEBUG_CMPXCHG
        printk(KERN_INFO "%s %s: cmpxchg double redo ", n, s->name);
#endif

        return 0;
}

#ifdef CONFIG_SLUB_DEBUG
/*
 * Determine a map of object in use on a page.
 *
 * Node listlock must be held to guarantee that the page does
 * not vanish from under us.
 */
static void get_map(struct kmem_cache *s, struct page *page, unsigned long *map)
{
        void *p;
        void *addr = page_address(page);

        for (p = page->freelist; p; p = get_freepointer(s, p))
                set_bit(slab_index(p, s, addr), map);
}

static inline int size_from_object(struct kmem_cache *s)
{
        if (s->flags & SLAB_RED_ZONE)
                return s->size - s->red_left_pad;

        return s->size;
}

static inline void *restore_red_left(struct kmem_cache *s, void *p)
{
        if (s->flags & SLAB_RED_ZONE)
                p -= s->red_left_pad;

        return p;
}

/*
 * Debug settings:
 */
#ifdef CONFIG_SLUB_DEBUG_ON
static int slub_debug = DEBUG_DEFAULT_FLAGS;
#else
static int slub_debug;
#endif

static char *slub_debug_slabs;
static int disable_higher_order_debug;

/*
 * Object debugging
 */

/* Verify that a pointer has an address that is valid within a slab page */
static inline int check_valid_pointer(struct kmem_cache *s,
                                struct page *page, void *object)
{
        void *base;

        if (!object)
                return 1;

        base = page_address(page);
        object = restore_red_left(s, object);
        if (object < base || object >= base + page->objects * s->size ||
                (object - base) % s->size) {
                return 0;
        }

        return 1;
}

static void print_section(char *text, u8 *addr, unsigned int length)
{
        print_hex_dump(KERN_ERR, text, DUMP_PREFIX_ADDRESS, 16, 1, addr,
                        length, 1);
}

static struct track *get_track(struct kmem_cache *s, void *object,
        enum track_item alloc)
{
        struct track *p;

        if (s->offset)
                p = object + s->offset + sizeof(void *);
        else
                p = object + s->inuse;

        return p + alloc;
}

static void set_track(struct kmem_cache *s, void *object,
                        enum track_item alloc, unsigned long addr)
{
        struct track *p = get_track(s, object, alloc);

        if (addr) {
#ifdef CONFIG_STACKTRACE
                struct stack_trace trace;
                int i;

                trace.nr_entries = 0;
                trace.max_entries = TRACK_ADDRS_COUNT;
                trace.entries = p->addrs;
                trace.skip = 3;
                save_stack_trace(&trace);

                /* See rant in lockdep.c */
                if (trace.nr_entries != 0 &&
                    trace.entries[trace.nr_entries - 1] == ULONG_MAX)
                        trace.nr_entries--;

                for (i = trace.nr_entries; i < TRACK_ADDRS_COUNT; i++)
                        p->addrs[i] = 0;
#endif
                p->addr = addr;
                p->cpu = smp_processor_id();
                p->pid = current->pid;
                p->when = jiffies;
        } else
                memset(p, 0, sizeof(struct track));
}

static void init_tracking(struct kmem_cache *s, void *object)
{
        if (!(s->flags & SLAB_STORE_USER))
                return;

        set_track(s, object, TRACK_FREE, 0UL);
        set_track(s, object, TRACK_ALLOC, 0UL);
}

static void print_track(const char *s, struct track *t)
{
        if (!t->addr)
                return;

        printk(KERN_ERR "INFO: %s in %pS age=%lu cpu=%u pid=%d\n",
                s, (void *)t->addr, jiffies - t->when, t->cpu, t->pid);
#ifdef CONFIG_STACKTRACE
        {
                int i;
                for (i = 0; i < TRACK_ADDRS_COUNT; i++)
                        if (t->addrs[i])
                                printk(KERN_ERR "\t%pS\n", (void *)t->addrs[i]);
                        else
                                break;
        }
#endif
}

static void print_tracking(struct kmem_cache *s, void *object)
{
        if (!(s->flags & SLAB_STORE_USER))
                return;

        print_track("Allocated", get_track(s, object, TRACK_ALLOC));
        print_track("Freed", get_track(s, object, TRACK_FREE));
}

static void print_page_info(struct page *page)
{
        printk(KERN_ERR "INFO: Slab 0x%p objects=%u used=%u fp=0x%p flags=0x%04lx\n",
                page, page->objects, page->inuse, page->freelist, page->flags);

}

static void slab_bug(struct kmem_cache *s, char *fmt, ...)
{
        va_list args;
        char buf[100];

        va_start(args, fmt);
        vsnprintf(buf, sizeof(buf), fmt, args);
        va_end(args);
        printk(KERN_ERR "========================================"
                        "=====================================\n");
        printk(KERN_ERR "BUG %s (%s): %s\n", s->name, print_tainted(), buf);
        printk(KERN_ERR "----------------------------------------"
                        "-------------------------------------\n\n");

        add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
}

static void slab_fix(struct kmem_cache *s, char *fmt, ...)
{
        va_list args;
        char buf[100];

        va_start(args, fmt);
        vsnprintf(buf, sizeof(buf), fmt, args);
        va_end(args);
        printk(KERN_ERR "FIX %s: %s\n", s->name, buf);
}

static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p)
{
        unsigned int off;       /* Offset of last byte */
        u8 *addr = page_address(page);

        print_tracking(s, p);

        print_page_info(page);

        printk(KERN_ERR "INFO: Object 0x%p @offset=%tu fp=0x%p\n\n",
                        p, p - addr, get_freepointer(s, p));

        if (s->flags & SLAB_RED_ZONE)
                print_section("Redzone ", p - s->red_left_pad, s->red_left_pad);
        else if (p > addr + 16)
                print_section("Bytes b4 ", p - 16, 16);

        print_section("Object ", p, min_t(unsigned long, s->object_size,
                                PAGE_SIZE));
        if (s->flags & SLAB_RED_ZONE)
                print_section("Redzone ", p + s->object_size,
                        s->inuse - s->object_size);

        if (s->offset)
                off = s->offset + sizeof(void *);
        else
                off = s->inuse;

        if (s->flags & SLAB_STORE_USER)
                off += 2 * sizeof(struct track);

        if (off != size_from_object(s))
                /* Beginning of the filler is the free pointer */
                print_section("Padding ", p + off, size_from_object(s) - off);

        dump_stack();
}

static void object_err(struct kmem_cache *s, struct page *page,
                        u8 *object, char *reason)
{
        slab_bug(s, "%s", reason);
        print_trailer(s, page, object);
}

static void slab_err(struct kmem_cache *s, struct page *page, const char *fmt, ...)
{
        va_list args;
        char buf[100];

        va_start(args, fmt);
        vsnprintf(buf, sizeof(buf), fmt, args);
        va_end(args);
        slab_bug(s, "%s", buf);
        print_page_info(page);
        dump_stack();
}

static void init_object(struct kmem_cache *s, void *object, u8 val)
{
        u8 *p = object;

        if (s->flags & SLAB_RED_ZONE)
                memset(p - s->red_left_pad, val, s->red_left_pad);

        if (s->flags & __OBJECT_POISON) {
                memset(p, POISON_FREE, s->object_size - 1);
                p[s->object_size - 1] = POISON_END;
        }

        if (s->flags & SLAB_RED_ZONE)
                memset(p + s->object_size, val, s->inuse - s->object_size);
}

static void restore_bytes(struct kmem_cache *s, char *message, u8 data,
                                                void *from, void *to)
{
        slab_fix(s, "Restoring 0x%p-0x%p=0x%x\n", from, to - 1, data);
        memset(from, data, to - from);
}

static int check_bytes_and_report(struct kmem_cache *s, struct page *page,
                        u8 *object, char *what,
                        u8 *start, unsigned int value, unsigned int bytes)
{
        u8 *fault;
        u8 *end;

        fault = memchr_inv(start, value, bytes);
        if (!fault)
                return 1;

        end = start + bytes;
        while (end > fault && end[-1] == value)
                end--;

        slab_bug(s, "%s overwritten", what);
        printk(KERN_ERR "INFO: 0x%p-0x%p. First byte 0x%x instead of 0x%x\n",
                                        fault, end - 1, fault[0], value);
        print_trailer(s, page, object);

        restore_bytes(s, what, value, fault, end);
        return 0;
}

/*
 * Object layout:
 *
 * object address
 *      Bytes of the object to be managed.
 *      If the freepointer may overlay the object then the free
 *      pointer is the first word of the object.
 *
 *      Poisoning uses 0x6b (POISON_FREE) and the last byte is
 *      0xa5 (POISON_END)
 *
 * object + s->object_size
 *      Padding to reach word boundary. This is also used for Redzoning.
 *      Padding is extended by another word if Redzoning is enabled and
 *      object_size == inuse.
 *
 *      We fill with 0xbb (RED_INACTIVE) for inactive objects and with
 *      0xcc (RED_ACTIVE) for objects in use.
 *
 * object + s->inuse
 *      Meta data starts here.
 *
 *      A. Free pointer (if we cannot overwrite object on free)
 *      B. Tracking data for SLAB_STORE_USER
 *      C. Padding to reach required alignment boundary or at mininum
 *              one word if debugging is on to be able to detect writes
 *              before the word boundary.
 *
 *      Padding is done using 0x5a (POISON_INUSE)
 *
 * object + s->size
 *      Nothing is used beyond s->size.
 *
 * If slabcaches are merged then the object_size and inuse boundaries are mostly
 * ignored. And therefore no slab options that rely on these boundaries
 * may be used with merged slabcaches.
 */

static int check_pad_bytes(struct kmem_cache *s, struct page *page, u8 *p)
{
        unsigned long off = s->inuse;   /* The end of info */

        if (s->offset)
                /* Freepointer is placed after the object. */
                off += sizeof(void *);

        if (s->flags & SLAB_STORE_USER)
                /* We also have user information there */
                off += 2 * sizeof(struct track);

        if (size_from_object(s) == off)
                return 1;

        return check_bytes_and_report(s, page, p, "Object padding",
                        p + off, POISON_INUSE, size_from_object(s) - off);
}

/* Check the pad bytes at the end of a slab page */
static int slab_pad_check(struct kmem_cache *s, struct page *page)
{
        u8 *start;
        u8 *fault;
        u8 *end;
        int length;
        int remainder;

        if (!(s->flags & SLAB_POISON))
                return 1;

        start = page_address(page);
        length = (PAGE_SIZE << compound_order(page)) - s->reserved;
        end = start + length;
        remainder = length % s->size;
        if (!remainder)
                return 1;

        fault = memchr_inv(end - remainder, POISON_INUSE, remainder);
        if (!fault)
                return 1;
        while (end > fault && end[-1] == POISON_INUSE)
                end--;

        slab_err(s, page, "Padding overwritten. 0x%p-0x%p", fault, end - 1);
        print_section("Padding ", end - remainder, remainder);

        restore_bytes(s, "slab padding", POISON_INUSE, end - remainder, end);
        return 0;
}

static int check_object(struct kmem_cache *s, struct page *page,
                                        void *object, u8 val)
{
        u8 *p = object;
        u8 *endobject = object + s->object_size;

        if (s->flags & SLAB_RED_ZONE) {
                if (!check_bytes_and_report(s, page, object, "Redzone",
                        object - s->red_left_pad, val, s->red_left_pad))
                        return 0;

                if (!check_bytes_and_report(s, page, object, "Redzone",
                        endobject, val, s->inuse - s->object_size))
                        return 0;
        } else {
                if ((s->flags & SLAB_POISON) && s->object_size < s->inuse) {
                        check_bytes_and_report(s, page, p, "Alignment padding",
                                endobject, POISON_INUSE, s->inuse - s->object_size);
                }
        }

        if (s->flags & SLAB_POISON) {
                if (val != SLUB_RED_ACTIVE && (s->flags & __OBJECT_POISON) &&
                        (!check_bytes_and_report(s, page, p, "Poison", p,
                                        POISON_FREE, s->object_size - 1) ||
                         !check_bytes_and_report(s, page, p, "Poison",
                                p + s->object_size - 1, POISON_END, 1)))
                        return 0;
                /*
                 * check_pad_bytes cleans up on its own.
                 */
                check_pad_bytes(s, page, p);
        }

        if (!s->offset && val == SLUB_RED_ACTIVE)
                /*
                 * Object and freepointer overlap. Cannot check
                 * freepointer while object is allocated.
                 */
                return 1;

        /* Check free pointer validity */
        if (!check_valid_pointer(s, page, get_freepointer(s, p))) {
                object_err(s, page, p, "Freepointer corrupt");
                /*
                 * No choice but to zap it and thus lose the remainder
                 * of the free objects in this slab. May cause
                 * another error because the object count is now wrong.
                 */
                set_freepointer(s, p, NULL);
                return 0;
        }
        return 1;
}

static int check_slab(struct kmem_cache *s, struct page *page)
{
        int maxobj;

        VM_BUG_ON(!irqs_disabled());

        if (!PageSlab(page)) {
                slab_err(s, page, "Not a valid slab page");
                return 0;
        }

        maxobj = order_objects(compound_order(page), s->size, s->reserved);
        if (page->objects > maxobj) {
                slab_err(s, page, "objects %u > max %u",
                        s->name, page->objects, maxobj);
                return 0;
        }
        if (page->inuse > page->objects) {
                slab_err(s, page, "inuse %u > max %u",
                        s->name, page->inuse, page->objects);
                return 0;
        }
        /* Slab_pad_check fixes things up after itself */
        slab_pad_check(s, page);
        return 1;
}

/*
 * Determine if a certain object on a page is on the freelist. Must hold the
 * slab lock to guarantee that the chains are in a consistent state.
 */
static int on_freelist(struct kmem_cache *s, struct page *page, void *search)
{
        int nr = 0;
        void *fp;
        void *object = NULL;
        unsigned long max_objects;

        fp = page->freelist;
        while (fp && nr <= page->objects) {
                if (fp == search)
                        return 1;
                if (!check_valid_pointer(s, page, fp)) {
                        if (object) {
                                object_err(s, page, object,
                                        "Freechain corrupt");
                                set_freepointer(s, object, NULL);
                                break;
                        } else {
                                slab_err(s, page, "Freepointer corrupt");
                                page->freelist = NULL;
                                page->inuse = page->objects;
                                slab_fix(s, "Freelist cleared");
                                return 0;
                        }
                        break;
                }
                object = fp;
                fp = get_freepointer(s, object);
                nr++;
        }

        max_objects = order_objects(compound_order(page), s->size, s->reserved);
        if (max_objects > MAX_OBJS_PER_PAGE)
                max_objects = MAX_OBJS_PER_PAGE;

        if (page->objects != max_objects) {
                slab_err(s, page, "Wrong number of objects. Found %d but "
                        "should be %d", page->objects, max_objects);
                page->objects = max_objects;
                slab_fix(s, "Number of objects adjusted.");
        }
        if (page->inuse != page->objects - nr) {
                slab_err(s, page, "Wrong object count. Counter is %d but "
                        "counted were %d", page->inuse, page->objects - nr);
                page->inuse = page->objects - nr;
                slab_fix(s, "Object count adjusted.");
        }
        return search == NULL;
}

static void trace(struct kmem_cache *s, struct page *page, void *object,
                                                                int alloc)
{
        if (s->flags & SLAB_TRACE) {
                printk(KERN_INFO "TRACE %s %s 0x%p inuse=%d fp=0x%p\n",
                        s->name,
                        alloc ? "alloc" : "free",
                        object, page->inuse,
                        page->freelist);

                if (!alloc)
                        print_section("Object ", (void *)object, s->object_size);

                dump_stack();
        }
}

/*
 * Hooks for other subsystems that check memory allocations. In a typical
 * production configuration these hooks all should produce no code at all.
 */
static inline int slab_pre_alloc_hook(struct kmem_cache *s, gfp_t flags)
{
        flags &= gfp_allowed_mask;
        lockdep_trace_alloc(flags);
        might_sleep_if(flags & __GFP_WAIT);

        return should_failslab(s->object_size, flags, s->flags);
}

static inline void slab_post_alloc_hook(struct kmem_cache *s, gfp_t flags,
                                        size_t size, void **p)
{
        size_t i;

        flags &= gfp_allowed_mask;
        for (i = 0; i < size; i++) {

                void *object = p[i];

                kmemcheck_slab_alloc(s, flags, object, slab_ksize(s));
                kmemleak_alloc_recursive(object, s->object_size, 1,
                                         s->flags, flags);
        }
}

static inline void slab_free_hook(struct kmem_cache *s, void *x)
{
        kmemleak_free_recursive(x, s->flags);

        /*
         * Trouble is that we may no longer disable interupts in the fast path
         * So in order to make the debug calls that expect irqs to be
         * disabled we need to disable interrupts temporarily.
         */
#if defined(CONFIG_KMEMCHECK) || defined(CONFIG_LOCKDEP)
        {
                unsigned long flags;

                local_irq_save(flags);
                kmemcheck_slab_free(s, x, s->object_size);
                debug_check_no_locks_freed(x, s->object_size);
                local_irq_restore(flags);
        }
#endif
        if (!(s->flags & SLAB_DEBUG_OBJECTS))
                debug_check_no_obj_freed(x, s->object_size);
}

/*
 * Tracking of fully allocated slabs for debugging purposes.
 *
 * list_lock must be held.
 */
static void add_full(struct kmem_cache *s,
        struct kmem_cache_node *n, struct page *page)
{
        if (!(s->flags & SLAB_STORE_USER))
                return;

        list_add(&page->lru, &n->full);
}

/*
 * list_lock must be held.
 */
static void remove_full(struct kmem_cache *s, struct page *page)
{
        if (!(s->flags & SLAB_STORE_USER))
                return;

        list_del(&page->lru);
}

/* Tracking of the number of slabs for debugging purposes */
static inline unsigned long slabs_node(struct kmem_cache *s, int node)
{
        struct kmem_cache_node *n = get_node(s, node);

        return atomic_long_read(&n->nr_slabs);
}

static inline unsigned long node_nr_slabs(struct kmem_cache_node *n)
{
        return atomic_long_read(&n->nr_slabs);
}

static inline void inc_slabs_node(struct kmem_cache *s, int node, int objects)
{
        struct kmem_cache_node *n = get_node(s, node);

        /*
         * May be called early in order to allocate a slab for the
         * kmem_cache_node structure. Solve the chicken-egg
         * dilemma by deferring the increment of the count during
         * bootstrap (see early_kmem_cache_node_alloc).
         */
        if (likely(n)) {
                atomic_long_inc(&n->nr_slabs);
                atomic_long_add(objects, &n->total_objects);
        }
}
static inline void dec_slabs_node(struct kmem_cache *s, int node, int objects)
{
        struct kmem_cache_node *n = get_node(s, node);

        atomic_long_dec(&n->nr_slabs);
        atomic_long_sub(objects, &n->total_objects);
}

/* Object debug checks for alloc/free paths */
static void setup_object_debug(struct kmem_cache *s, struct page *page,
                                                                void *object)
{
        if (!(s->flags & (SLAB_STORE_USER|SLAB_RED_ZONE|__OBJECT_POISON)))
                return;

        init_object(s, object, SLUB_RED_INACTIVE);
        init_tracking(s, object);
}

static inline int alloc_consistency_checks(struct kmem_cache *s, struct page *page,
                                        void *object)
{
        if (!check_slab(s, page))
                return 0;

        if (!check_valid_pointer(s, page, object)) {
                object_err(s, page, object, "Freelist Pointer check fails");
                return 0;
        }

        if (!check_object(s, page, object, SLUB_RED_INACTIVE))
                return 0;

        return 1;
}

static noinline int alloc_debug_processing(struct kmem_cache *s,
                                        struct page *page,
                                        void *object, unsigned long addr)
{
        if (s->flags & SLAB_CONSISTENCY_CHECKS) {
                if (!alloc_consistency_checks(s, page, object))
                        goto bad;
        }

        /* Success perform special debug activities for allocs */
        if (s->flags & SLAB_STORE_USER)
                set_track(s, object, TRACK_ALLOC, addr);
        trace(s, page, object, 1);
        init_object(s, object, SLUB_RED_ACTIVE);
        return 1;

bad:
        if (PageSlab(page)) {
                /*
                 * If this is a slab page then lets do the best we can
                 * to avoid issues in the future. Marking all objects
                 * as used avoids touching the remaining objects.
                 */
                slab_fix(s, "Marking all objects used");
                page->inuse = page->objects;
                page->freelist = NULL;
        }
        return 0;
}

static inline int free_consistency_checks(struct kmem_cache *s,
                struct page *page, void *object, unsigned long addr)
{
        if (!check_valid_pointer(s, page, object)) {
                slab_err(s, page, "Invalid object pointer 0x%p", object);
                return 0;
        }

        if (on_freelist(s, page, object)) {
                object_err(s, page, object, "Object already free");
                return 0;
        }

        if (!check_object(s, page, object, SLUB_RED_ACTIVE))
                return 0;

        if (unlikely(s != page->slab_cache)) {
                if (!PageSlab(page)) {
                        slab_err(s, page, "Attempt to free object(0x%p) "
                                "outside of slab", object);
                } else if (!page->slab_cache) {
                        printk(KERN_ERR
                                "SLUB <none>: no slab for object 0x%p.\n",
                                                object);
                        dump_stack();
                } else
                        object_err(s, page, object,
                                        "page slab pointer corrupt.");
                return 0;
        }
        return 1;
}

/* Supports checking bulk free of a constructed freelist */
static noinline int free_debug_processing(
        struct kmem_cache *s, struct page *page,
        void *head, void *tail, int bulk_cnt,
        unsigned long addr)
{
        struct kmem_cache_node *n = get_node(s, page_to_nid(page));
        void *object = head;
        int cnt = 0;
        unsigned long uninitialized_var(flags);
        int ret = 0;

        spin_lock_irqsave(&n->list_lock, flags);
        slab_lock(page);

        if (s->flags & SLAB_CONSISTENCY_CHECKS) {
                if (!check_slab(s, page))
                        goto out;
        }

next_object:
        cnt++;

        if (s->flags & SLAB_CONSISTENCY_CHECKS) {
                if (!free_consistency_checks(s, page, object, addr))
                        goto out;
        }

        if (s->flags & SLAB_STORE_USER)
                set_track(s, object, TRACK_FREE, addr);
        trace(s, page, object, 0);
        /* Freepointer not overwritten by init_object(), SLAB_POISON moved it */
        init_object(s, object, SLUB_RED_INACTIVE);

        /* Reached end of constructed freelist yet? */
        if (object != tail) {
                object = get_freepointer(s, object);
                goto next_object;
        }
        ret = 1;

out:
        if (cnt != bulk_cnt)
                slab_err(s, page, "Bulk freelist count(%d) invalid(%d)\n",
                         bulk_cnt, cnt);

        slab_unlock(page);
        spin_unlock_irqrestore(&n->list_lock, flags);
        if (!ret)
                slab_fix(s, "Object at 0x%p not freed", object);
        return ret;
}

static int __init setup_slub_debug(char *str)
{
        slub_debug = DEBUG_DEFAULT_FLAGS;
        if (*str++ != '=' || !*str)
                /*
                 * No options specified. Switch on full debugging.
                 */
                goto out;

        if (*str == ',')
                /*
                 * No options but restriction on slabs. This means full
                 * debugging for slabs matching a pattern.
                 */
                goto check_slabs;

        if (tolower(*str) == 'o') {
                /*
                 * Avoid enabling debugging on caches if its minimum order
                 * would increase as a result.
                 */
                disable_higher_order_debug = 1;
                goto out;
        }

        slub_debug = 0;
        if (*str == '-')
                /*
                 * Switch off all debugging measures.
                 */
                goto out;

        /*
         * Determine which debug features should be switched on
         */
        for (; *str && *str != ','; str++) {
                switch (tolower(*str)) {
                case 'f':
                        slub_debug |= SLAB_CONSISTENCY_CHECKS;
                        break;
                case 'z':
                        slub_debug |= SLAB_RED_ZONE;
                        break;
                case 'p':
                        slub_debug |= SLAB_POISON;
                        break;
                case 'u':
                        slub_debug |= SLAB_STORE_USER;
                        break;
                case 't':
                        slub_debug |= SLAB_TRACE;
                        break;
                case 'a':
                        slub_debug |= SLAB_FAILSLAB;
                        break;
                default:
                        printk(KERN_ERR "slub_debug option '%c' "
                                "unknown. skipped\n", *str);
                }
        }

check_slabs:
        if (*str == ',')
                slub_debug_slabs = str + 1;
out:
        return 1;
}

__setup("slub_debug", setup_slub_debug);

/*
 * kmem_cache_flags - apply debugging options to the cache
 * @object_size:        the size of an object without meta data
 * @flags:              flags to set
 * @name:               name of the cache
 * @ctor:               constructor function
 *
 * Debug option(s) are applied to @flags. In addition to the debug
 * option(s), if a slab name (or multiple) is specified i.e.
 * slub_debug=<Debug-Options>,<slab name1>,<slab name2> ...
 * then only the select slabs will receive the debug option(s).
 */
static unsigned long kmem_cache_flags(unsigned long object_size,
        unsigned long flags, const char *name,
        void (*ctor)(void *))
{
        char *iter;
        size_t len;

        /* If slub_debug = 0, it folds into the if conditional. */
        if (!slub_debug_slabs)
                return flags | slub_debug;

        len = strlen(name);
        iter = slub_debug_slabs;
        while (*iter) {
                char *end, *glob;
                size_t cmplen;

                end = strchr(iter, ',');
                if (!end)
                        end = iter + strlen(iter);

                glob = strnchr(iter, end - iter, '*');
                if (glob)
                        cmplen = glob - iter;
                else
                        cmplen = max_t(size_t, len, (end - iter));

                if (!strncmp(name, iter, cmplen)) {
                        flags |= slub_debug;
                        break;
                }

                if (!*end)
                        break;
                iter = end + 1;
        }

        return flags;
}
#else /* !CONFIG_SLUB_DEBUG */
static inline void setup_object_debug(struct kmem_cache *s,
                        struct page *page, void *object) {}

static inline int alloc_debug_processing(struct kmem_cache *s,
        struct page *page, void *object, unsigned long addr) { return 0; }

static inline int free_debug_processing(
        struct kmem_cache *s, struct page *page,
        void *head, void *tail, int bulk_cnt,
        unsigned long addr) { return 0; }

static inline int slab_pad_check(struct kmem_cache *s, struct page *page)
                        { return 1; }
static inline int check_object(struct kmem_cache *s, struct page *page,
                        void *object, u8 val) { return 1; }
static inline void add_full(struct kmem_cache *s, struct kmem_cache_node *n,
                                        struct page *page) {}
static inline void remove_full(struct kmem_cache *s, struct page *page) {}
static inline unsigned long kmem_cache_flags(unsigned long object_size,
        unsigned long flags, const char *name,
        void (*ctor)(void *))
{
        return flags;
}
#define slub_debug 0

#define disable_higher_order_debug 0

static inline unsigned long slabs_node(struct kmem_cache *s, int node)
                                                        { return 0; }
static inline unsigned long node_nr_slabs(struct kmem_cache_node *n)
                                                        { return 0; }
static inline void inc_slabs_node(struct kmem_cache *s, int node,
                                                        int objects) {}
static inline void dec_slabs_node(struct kmem_cache *s, int node,
                                                        int objects) {}

static inline int slab_pre_alloc_hook(struct kmem_cache *s, gfp_t flags)
                                                        { return 0; }

static inline void slab_post_alloc_hook(struct kmem_cache *s, gfp_t flags,
                void *object) {}

static inline void slab_free_hook(struct kmem_cache *s, void *x) {}

#endif /* CONFIG_SLUB_DEBUG */

static inline void slab_free_freelist_hook(struct kmem_cache *s,
                                           void *head, void *tail)
{
/*
 * Compiler cannot detect this function can be removed if slab_free_hook()
 * evaluates to nothing.  Thus, catch all relevant config debug options here.
 */
#if defined(CONFIG_KMEMCHECK) ||                \
        defined(CONFIG_LOCKDEP) ||              \
        defined(CONFIG_DEBUG_KMEMLEAK) ||       \
        defined(CONFIG_DEBUG_OBJECTS_FREE) ||   \
        defined(CONFIG_KASAN)

        void *object = head;
        void *tail_obj = tail ? : head;

        do {
                slab_free_hook(s, object);
        } while ((object != tail_obj) &&
                 (object = get_freepointer(s, object)));
#endif
}

/*
 * Slab allocation and freeing
 */
static inline struct page *alloc_slab_page(struct kmem_cache *s,
                gfp_t flags, int node, struct kmem_cache_order_objects oo)
{
        struct page *page;
        int order = oo_order(oo);

        flags |= __GFP_NOTRACK;

        if (memcg_charge_slab(s, flags, order))
                return NULL;

        if (node == NUMA_NO_NODE)
                page = alloc_pages(flags, order);
        else
                page = alloc_pages_exact_node(node, flags, order);

        if (!page)
                memcg_uncharge_slab(s, order);

        return page;
}

static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
{
        struct page *page;
        struct kmem_cache_order_objects oo = s->oo;
        gfp_t alloc_gfp;

        flags &= gfp_allowed_mask;

        if (flags & __GFP_WAIT)
                local_irq_enable();

        flags |= s->allocflags;

        /*
         * Let the initial higher-order allocation fail under memory pressure
         * so we fall-back to the minimum order allocation.
         */
        alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY) & ~__GFP_NOFAIL;

        page = alloc_slab_page(s, alloc_gfp, node, oo);
        if (unlikely(!page)) {
                oo = s->min;
                /*
                 * Allocation may have failed due to fragmentation.
                 * Try a lower order alloc if possible
                 */
                page = alloc_slab_page(s, flags, node, oo);

                if (page)
                        stat(s, ORDER_FALLBACK);
        }

        if (kmemcheck_enabled && page
                && !(s->flags & (SLAB_NOTRACK | DEBUG_DEFAULT_FLAGS))) {
                int pages = 1 << oo_order(oo);

                kmemcheck_alloc_shadow(page, oo_order(oo), flags, node);

                /*
                 * Objects from caches that have a constructor don't get
                 * cleared when they're allocated, so we need to do it here.
                 */
                if (s->ctor)
                        kmemcheck_mark_uninitialized_pages(page, pages);
                else
                        kmemcheck_mark_unallocated_pages(page, pages);
        }

        if (flags & __GFP_WAIT)
                local_irq_disable();
        if (!page)
                return NULL;

        page->objects = oo_objects(oo);
        mod_zone_page_state(page_zone(page),
                (s->flags & SLAB_RECLAIM_ACCOUNT) ?
                NR_SLAB_RECLAIMABLE : NR_SLAB_UNRECLAIMABLE,
                1 << oo_order(oo));

        return page;
}

static void setup_object(struct kmem_cache *s, struct page *page,
                                void *object)
{
        setup_object_debug(s, page, object);
        if (unlikely(s->ctor))
                s->ctor(object);
}

static struct page *new_slab(struct kmem_cache *s, gfp_t flags, int node)
{
        struct page *page;
        void *start;
        void *p;
        int order;
        int idx;

        BUG_ON(flags & GFP_SLAB_BUG_MASK);

        page = allocate_slab(s,
                flags & (GFP_RECLAIM_MASK | GFP_CONSTRAINT_MASK), node);
        if (!page)
                goto out;

        order = compound_order(page);
        inc_slabs_node(s, page_to_nid(page), page->objects);
        memcg_bind_pages(s, order);
        page->slab_cache = s;
        __SetPageSlab(page);
        if (page_is_pfmemalloc(page))
                SetPageSlabPfmemalloc(page);

        start = page_address(page);

        if (unlikely(s->flags & SLAB_POISON))
                memset(start, POISON_INUSE, PAGE_SIZE << order);

        for_each_object_idx(p, idx, s, start, page->objects) {
                setup_object(s, page, p);
                if (likely(idx < page->objects))
                        set_freepointer(s, p, p + s->size);
                else
                        set_freepointer(s, p, NULL);
        }

        page->freelist = fixup_red_left(s, start);
        page->inuse = page->objects;
        page->frozen = 1;
out:
        return page;
}

static void __free_slab(struct kmem_cache *s, struct page *page)
{
        int order = compound_order(page);
        int pages = 1 << order;

        if (s->flags & SLAB_CONSISTENCY_CHECKS) {
                void *p;

                slab_pad_check(s, page);
                for_each_object(p, s, page_address(page),
                                                page->objects)
                        check_object(s, page, p, SLUB_RED_INACTIVE);
        }

        kmemcheck_free_shadow(page, compound_order(page));

        mod_zone_page_state(page_zone(page),
                (s->flags & SLAB_RECLAIM_ACCOUNT) ?
                NR_SLAB_RECLAIMABLE : NR_SLAB_UNRECLAIMABLE,
                -pages);

        __ClearPageSlabPfmemalloc(page);
        __ClearPageSlab(page);

        memcg_release_pages(s, order);
        page_mapcount_reset(page);
        if (current->reclaim_state)
                current->reclaim_state->reclaimed_slab += pages;
        __free_pages(page, order);
        memcg_uncharge_slab(s, order);
}

#define need_reserve_slab_rcu                                           \
        (sizeof(((struct page *)NULL)->lru) < sizeof(struct rcu_head))

static void rcu_free_slab(struct rcu_head *h)
{
        struct page *page;

        if (need_reserve_slab_rcu)
                page = virt_to_head_page(h);
        else
                page = container_of((struct list_head *)h, struct page, lru);

        __free_slab(page->slab_cache, page);
}

static void free_slab(struct kmem_cache *s, struct page *page)
{
        if (unlikely(s->flags & SLAB_DESTROY_BY_RCU)) {
                struct rcu_head *head;

                if (need_reserve_slab_rcu) {
                        int order = compound_order(page);
                        int offset = (PAGE_SIZE << order) - s->reserved;

                        VM_BUG_ON(s->reserved != sizeof(*head));
                        head = page_address(page) + offset;
                } else {
                        /*
                         * RCU free overloads the RCU head over the LRU
                         */
                        head = (void *)&page->lru;
                }

                call_rcu(head, rcu_free_slab);
        } else
                __free_slab(s, page);
}

static void discard_slab(struct kmem_cache *s, struct page *page)
{
        dec_slabs_node(s, page_to_nid(page), page->objects);
        free_slab(s, page);
}

/*
 * Management of partially allocated slabs.
 *
 * list_lock must be held.
 */
static inline void add_partial(struct kmem_cache_node *n,
                                struct page *page, int tail)
{
        n->nr_partial++;
        if (tail == DEACTIVATE_TO_TAIL)
                list_add_tail(&page->lru, &n->partial);
        else
                list_add(&page->lru, &n->partial);
}

/*
 * list_lock must be held.
 */
static inline void remove_partial(struct kmem_cache_node *n,
                                        struct page *page)
{
        list_del(&page->lru);
        n->nr_partial--;
}

/*
 * Remove slab from the partial list, freeze it and
 * return the pointer to the freelist.
 *
 * Returns a list of objects or NULL if it fails.
 *
 * Must hold list_lock since we modify the partial list.
 */
static inline void *acquire_slab(struct kmem_cache *s,
                struct kmem_cache_node *n, struct page *page,
                int mode, int *objects)
{
        void *freelist;
        unsigned long counters;
        struct page new;

        /*
         * Zap the freelist and set the frozen bit.
         * The old freelist is the list of objects for the
         * per cpu allocation list.
         */
        freelist = page->freelist;
        counters = page->counters;
        new.counters = counters;
        *objects = new.objects - new.inuse;
        if (mode) {
                new.inuse = page->objects;
                new.freelist = NULL;
        } else {
                new.freelist = freelist;
        }

        VM_BUG_ON(new.frozen);
        new.frozen = 1;

        if (!__cmpxchg_double_slab(s, page,
                        freelist, counters,
                        new.freelist, new.counters,
                        "acquire_slab"))
                return NULL;

        remove_partial(n, page);
        WARN_ON(!freelist);
        return freelist;
}

static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain);
static inline bool pfmemalloc_match(struct page *page, gfp_t gfpflags);

/*
 * Try to allocate a partial slab from a specific node.
 */
static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
                                struct kmem_cache_cpu *c, gfp_t flags)
{
        struct page *page, *page2;
        void *object = NULL;
        int available = 0;
        int objects;

        /*
         * Racy check. If we mistakenly see no partial slabs then we
         * just allocate an empty slab. If we mistakenly try to get a
         * partial slab and there is none available then get_partials()
         * will return NULL.
         */
        if (!n || !n->nr_partial)
                return NULL;

        spin_lock(&n->list_lock);
        list_for_each_entry_safe(page, page2, &n->partial, lru) {
                void *t;

                if (!pfmemalloc_match(page, flags))
                        continue;

                t = acquire_slab(s, n, page, object == NULL, &objects);
                if (!t)
                        break;

                available += objects;
                if (!object) {
                        c->page = page;
                        stat(s, ALLOC_FROM_PARTIAL);
                        object = t;
                } else {
                        put_cpu_partial(s, page, 0);
                        stat(s, CPU_PARTIAL_NODE);
                }
                if (kmem_cache_debug(s) || available > s->cpu_partial / 2)
                        break;

        }
        spin_unlock(&n->list_lock);
        return object;
}

/*
 * Get a page from somewhere. Search in increasing NUMA distances.
 */
static void *get_any_partial(struct kmem_cache *s, gfp_t flags,
                struct kmem_cache_cpu *c)
{
#ifdef CONFIG_NUMA
        struct zonelist *zonelist;
        struct zoneref *z;
        struct zone *zone;
        enum zone_type high_zoneidx = gfp_zone(flags);
        void *object;
        unsigned int cpuset_mems_cookie;

        /*
         * The defrag ratio allows a configuration of the tradeoffs between
         * inter node defragmentation and node local allocations. A lower
         * defrag_ratio increases the tendency to do local allocations
         * instead of attempting to obtain partial slabs from other nodes.
         *
         * If the defrag_ratio is set to 0 then kmalloc() always
         * returns node local objects. If the ratio is higher then kmalloc()
         * may return off node objects because partial slabs are obtained
         * from other nodes and filled up.
         *
         * If /sys/kernel/slab/xx/defrag_ratio is set to 100 (which makes
         * defrag_ratio = 1000) then every (well almost) allocation will
         * first attempt to defrag slab caches on other nodes. This means
         * scanning over all nodes to look for partial slabs which may be
         * expensive if we do it every time we are trying to find a slab
         * with available objects.
         */
        if (!s->remote_node_defrag_ratio ||
                        get_cycles() % 1024 > s->remote_node_defrag_ratio)
                return NULL;

        do {
                cpuset_mems_cookie = read_mems_allowed_begin();
                zonelist = node_zonelist(slab_node(), flags);
                for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
                        struct kmem_cache_node *n;

                        n = get_node(s, zone_to_nid(zone));

                        if (n && cpuset_zone_allowed_hardwall(zone, flags) &&
                                        n->nr_partial > s->min_partial) {
                                object = get_partial_node(s, n, c, flags);
                                if (object) {
                                        /*
                                         * Don't check read_mems_allowed_retry()
                                         * here - if mems_allowed was updated in
                                         * parallel, that was a harmless race
                                         * between allocation and the cpuset
                                         * update
                                         */
                                        return object;
                                }
                        }
                }
        } while (read_mems_allowed_retry(cpuset_mems_cookie));
#endif
        return NULL;
}

/*
 * Get a partial page, lock it and return it.
 */
static void *get_partial(struct kmem_cache *s, gfp_t flags, int node,
                struct kmem_cache_cpu *c)
{
        void *object;
        int searchnode = node;

        if (node == NUMA_NO_NODE)
                searchnode = numa_mem_id();
        else if (!node_present_pages(node))
                searchnode = node_to_mem_node(node);

        object = get_partial_node(s, get_node(s, searchnode), c, flags);
        if (object || node != NUMA_NO_NODE)
                return object;

        return get_any_partial(s, flags, c);
}

#ifdef CONFIG_PREEMPT
/*
 * Calculate the next globally unique transaction for disambiguiation
 * during cmpxchg. The transactions start with the cpu number and are then
 * incremented by CONFIG_NR_CPUS.
 */
#define TID_STEP  roundup_pow_of_two(CONFIG_NR_CPUS)
#else
/*
 * No preemption supported therefore also no need to check for
 * different cpus.
 */
#define TID_STEP 1
#endif

static inline unsigned long next_tid(unsigned long tid)
{
        return tid + TID_STEP;
}

static inline unsigned int tid_to_cpu(unsigned long tid)
{
        return tid % TID_STEP;
}

static inline unsigned long tid_to_event(unsigned long tid)
{
        return tid / TID_STEP;
}

static inline unsigned int init_tid(int cpu)
{
        return cpu;
}

static inline void note_cmpxchg_failure(const char *n,
                const struct kmem_cache *s, unsigned long tid)
{
#ifdef SLUB_DEBUG_CMPXCHG
        unsigned long actual_tid = __this_cpu_read(s->cpu_slab->tid);

        printk(KERN_INFO "%s %s: cmpxchg redo ", n, s->name);

#ifdef CONFIG_PREEMPT
        if (tid_to_cpu(tid) != tid_to_cpu(actual_tid))
                printk("due to cpu change %d -> %d\n",
                        tid_to_cpu(tid), tid_to_cpu(actual_tid));
        else
#endif
        if (tid_to_event(tid) != tid_to_event(actual_tid))
                printk("due to cpu running other code. Event %ld->%ld\n",
                        tid_to_event(tid), tid_to_event(actual_tid));
        else
                printk("for unknown reason: actual=%lx was=%lx target=%lx\n",
                        actual_tid, tid, next_tid(tid));
#endif
        stat(s, CMPXCHG_DOUBLE_CPU_FAIL);
}

static void init_kmem_cache_cpus(struct kmem_cache *s)
{
        int cpu;

        for_each_possible_cpu(cpu)
                per_cpu_ptr(s->cpu_slab, cpu)->tid = init_tid(cpu);
}

/*
 * Remove the cpu slab
 */
static void deactivate_slab(struct kmem_cache *s, struct page *page, void *freelist)
{
        enum slab_modes { M_NONE, M_PARTIAL, M_FULL, M_FREE };
        struct kmem_cache_node *n = get_node(s, page_to_nid(page));
        int lock = 0;
        enum slab_modes l = M_NONE, m = M_NONE;
        void *nextfree;
        int tail = DEACTIVATE_TO_HEAD;
        struct page new;
        struct page old;

        if (page->freelist) {
                stat(s, DEACTIVATE_REMOTE_FREES);
                tail = DEACTIVATE_TO_TAIL;
        }

        /*
         * Stage one: Free all available per cpu objects back
         * to the page freelist while it is still frozen. Leave the
         * last one.
         *
         * There is no need to take the list->lock because the page
         * is still frozen.
         */
        while (freelist && (nextfree = get_freepointer(s, freelist))) {
                void *prior;
                unsigned long counters;

                do {
                        prior = page->freelist;
                        counters = page->counters;
                        set_freepointer(s, freelist, prior);
                        new.counters = counters;
                        new.inuse--;
                        VM_BUG_ON(!new.frozen);

                } while (!__cmpxchg_double_slab(s, page,
                        prior, counters,
                        freelist, new.counters,
                        "drain percpu freelist"));

                freelist = nextfree;
        }

        /*
         * Stage two: Ensure that the page is unfrozen while the
         * list presence reflects the actual number of objects
         * during unfreeze.
         *
         * We setup the list membership and then perform a cmpxchg
         * with the count. If there is a mismatch then the page
         * is not unfrozen but the page is on the wrong list.
         *
         * Then we restart the process which may have to remove
         * the page from the list that we just put it on again
         * because the number of objects in the slab may have
         * changed.
         */
redo:

        old.freelist = page->freelist;
        old.counters = page->counters;
        VM_BUG_ON(!old.frozen);

        /* Determine target state of the slab */
        new.counters = old.counters;
        if (freelist) {
                new.inuse--;
                set_freepointer(s, freelist, old.freelist);
                new.freelist = freelist;
        } else
                new.freelist = old.freelist;

        new.frozen = 0;

        if (!new.inuse && n->nr_partial > s->min_partial)
                m = M_FREE;
        else if (new.freelist) {
                m = M_PARTIAL;
                if (!lock) {
                        lock = 1;

                        /*
                         * Taking the spinlock removes the possiblity
                         * that acquire_slab() will see a slab page that
                         * is frozen
                         */
                        spin_lock(&n->list_lock);
                }
        } else {
                m = M_FULL;
                if (kmem_cache_debug(s) && !lock) {
                        lock = 1;
                        /*
                         * This also ensures that the scanning of full
                         * slabs from diagnostic functions will not see
                         * any frozen slabs.
                         */
                        spin_lock(&n->list_lock);
                }
        }

        if (l != m) {

                if (l == M_PARTIAL)

                        remove_partial(n, page);

                else if (l == M_FULL)

                        remove_full(s, page);

                if (m == M_PARTIAL) {

                        add_partial(n, page, tail);
                        stat(s, tail);

                } else if (m == M_FULL) {

                        stat(s, DEACTIVATE_FULL);
                        add_full(s, n, page);

                }
        }

        l = m;
        if (!__cmpxchg_double_slab(s, page,
                                old.freelist, old.counters,
                                new.freelist, new.counters,
                                "unfreezing slab"))
                goto redo;

        if (lock)
                spin_unlock(&n->list_lock);

        if (m == M_FREE) {
                stat(s, DEACTIVATE_EMPTY);
                discard_slab(s, page);
                stat(s, FREE_SLAB);
        }
}

/*
 * Unfreeze all the cpu partial slabs.
 *
 * This function must be called with interrupts disabled
 * for the cpu using c (or some other guarantee must be there
 * to guarantee no concurrent accesses).
 */
static void unfreeze_partials(struct kmem_cache *s,
                struct kmem_cache_cpu *c)
{
        struct kmem_cache_node *n = NULL, *n2 = NULL;
        struct page *page, *discard_page = NULL;

        while ((page = c->partial)) {
                struct page new;
                struct page old;

                c->partial = page->next;

                n2 = get_node(s, page_to_nid(page));
                if (n != n2) {
                        if (n)
                                spin_unlock(&n->list_lock);

                        n = n2;
                        spin_lock(&n->list_lock);
                }

                do {

                        old.freelist = page->freelist;
                        old.counters = page->counters;
                        VM_BUG_ON(!old.frozen);

                        new.counters = old.counters;
                        new.freelist = old.freelist;

                        new.frozen = 0;

                } while (!__cmpxchg_double_slab(s, page,
                                old.freelist, old.counters,
                                new.freelist, new.counters,
                                "unfreezing slab"));

                if (unlikely(!new.inuse && n->nr_partial > s->min_partial)) {
                        page->next = discard_page;
                        discard_page = page;
                } else {
                        add_partial(n, page, DEACTIVATE_TO_TAIL);
                        stat(s, FREE_ADD_PARTIAL);
                }
        }

        if (n)
                spin_unlock(&n->list_lock);

        while (discard_page) {
                page = discard_page;
                discard_page = discard_page->next;

                stat(s, DEACTIVATE_EMPTY);
                discard_slab(s, page);
                stat(s, FREE_SLAB);
        }
}

/*
 * Put a page that was just frozen (in __slab_free) into a partial page
 * slot if available. This is done without interrupts disabled and without
 * preemption disabled. The cmpxchg is racy and may put the partial page
 * onto a random cpus partial slot.
 *
 * If we did not find a slot then simply move all the partials to the
 * per node partial list.
 */
static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain)
{
        struct page *oldpage;
        int pages;
        int pobjects;

        preempt_disable();
        do {
                pages = 0;
                pobjects = 0;
                oldpage = this_cpu_read(s->cpu_slab->partial);

                if (oldpage) {
                        pobjects = oldpage->pobjects;
                        pages = oldpage->pages;
                        if (drain && pobjects > s->cpu_partial) {
                                unsigned long flags;
                                /*
                                 * partial array is full. Move the existing
                                 * set to the per node partial list.
                                 */
                                local_irq_save(flags);
                                unfreeze_partials(s, this_cpu_ptr(s->cpu_slab));
                                local_irq_restore(flags);
                                oldpage = NULL;
                                pobjects = 0;
                                pages = 0;
                                stat(s, CPU_PARTIAL_DRAIN);
                        }
                }

                pages++;
                pobjects += page->objects - page->inuse;

                page->pages = pages;
                page->pobjects = pobjects;
                page->next = oldpage;

        } while (this_cpu_cmpxchg(s->cpu_slab->partial, oldpage, page) != oldpage);

        if (unlikely(!s->cpu_partial)) {
                unsigned long flags;

                local_irq_save(flags);
                unfreeze_partials(s, this_cpu_ptr(s->cpu_slab));
                local_irq_restore(flags);
        }
        preempt_enable();
}

static inline void flush_slab(struct kmem_cache *s, struct kmem_cache_cpu *c)
{
        stat(s, CPUSLAB_FLUSH);
        deactivate_slab(s, c->page, c->freelist);

        c->tid = next_tid(c->tid);
        c->page = NULL;
        c->freelist = NULL;
}

/*
 * Flush cpu slab.
 *
 * Called from IPI handler with interrupts disabled.
 */
static inline void __flush_cpu_slab(struct kmem_cache *s, int cpu)
{
        struct kmem_cache_cpu *c = per_cpu_ptr(s->cpu_slab, cpu);

        if (likely(c)) {
                if (c->page)
                        flush_slab(s, c);

                unfreeze_partials(s, c);
        }
}

static void flush_cpu_slab(void *d)
{
        struct kmem_cache *s = d;

        __flush_cpu_slab(s, smp_processor_id());
}

static bool has_cpu_slab(int cpu, void *info)
{
        struct kmem_cache *s = info;
        struct kmem_cache_cpu *c = per_cpu_ptr(s->cpu_slab, cpu);

        return c->page || c->partial;
}

static void flush_all(struct kmem_cache *s)
{
        on_each_cpu_cond(has_cpu_slab, flush_cpu_slab, s, 1, GFP_ATOMIC);
}

/*
 * Check if the objects in a per cpu structure fit numa
 * locality expectations.
 */
static inline int node_match(struct page *page, int node)
{
#ifdef CONFIG_NUMA
        if (!page || (node != NUMA_NO_NODE && page_to_nid(page) != node))
                return 0;
#endif
        return 1;
}

static int count_free(struct page *page)
{
        return page->objects - page->inuse;
}

static unsigned long count_partial(struct kmem_cache_node *n,
                                        int (*get_count)(struct page *))
{
        unsigned long flags;
        unsigned long x = 0;
        struct page *page;

        spin_lock_irqsave(&n->list_lock, flags);
        list_for_each_entry(page, &n->partial, lru)
                x += get_count(page);
        spin_unlock_irqrestore(&n->list_lock, flags);
        return x;
}

static inline unsigned long node_nr_objs(struct kmem_cache_node *n)
{
#ifdef CONFIG_SLUB_DEBUG
        return atomic_long_read(&n->total_objects);
#else
        return 0;
#endif
}

static noinline void
slab_out_of_memory(struct kmem_cache *s, gfp_t gfpflags, int nid)
{
        int node;

        printk(KERN_WARNING
                "SLUB: Unable to allocate memory on node %d (gfp=0x%x)\n",
                nid, gfpflags);
        printk(KERN_WARNING "  cache: %s, object size: %d, buffer size: %d, "
                "default order: %d, min order: %d\n", s->name, s->object_size,
                s->size, oo_order(s->oo), oo_order(s->min));

        if (oo_order(s->min) > get_order(s->object_size))
                printk(KERN_WARNING "  %s debugging increased min order, use "
                       "slub_debug=O to disable.\n", s->name);

        for_each_online_node(node) {
                struct kmem_cache_node *n = get_node(s, node);
                unsigned long nr_slabs;
                unsigned long nr_objs;
                unsigned long nr_free;

                if (!n)
                        continue;

                nr_free  = count_partial(n, count_free);
                nr_slabs = node_nr_slabs(n);
                nr_objs  = node_nr_objs(n);

                printk(KERN_WARNING
                        "  node %d: slabs: %ld, objs: %ld, free: %ld\n",
                        node, nr_slabs, nr_objs, nr_free);
        }
}

static inline void *new_slab_objects(struct kmem_cache *s, gfp_t flags,
                        int node, struct kmem_cache_cpu **pc)
{
        void *freelist;
        struct kmem_cache_cpu *c = *pc;
        struct page *page;

        WARN_ON_ONCE(s->ctor && (flags & __GFP_ZERO));

        freelist = get_partial(s, flags, node, c);

        if (freelist)
                return freelist;

        page = new_slab(s, flags, node);
        if (page) {
                c = this_cpu_ptr(s->cpu_slab);
                if (c->page)
                        flush_slab(s, c);

                /*
                 * No other reference to the page yet so we can
                 * muck around with it freely without cmpxchg
                 */
                freelist = page->freelist;
                page->freelist = NULL;

                stat(s, ALLOC_SLAB);
                c->page = page;
                *pc = c;
        } else
                freelist = NULL;

        return freelist;
}

static inline bool pfmemalloc_match(struct page *page, gfp_t gfpflags)
{
        if (unlikely(PageSlabPfmemalloc(page)))
                return gfp_pfmemalloc_allowed(gfpflags);

        return true;
}

/*
 * Check the page->freelist of a page and either transfer the freelist to the per cpu freelist
 * or deactivate the page.
 *
 * The page is still frozen if the return value is not NULL.
 *
 * If this function returns NULL then the page has been unfrozen.
 *
 * This function must be called with interrupt disabled.
 */
static inline void *get_freelist(struct kmem_cache *s, struct page *page)
{
        struct page new;
        unsigned long counters;
        void *freelist;

        do {
                freelist = page->freelist;
                counters = page->counters;

                new.counters = counters;
                VM_BUG_ON(!new.frozen);

                new.inuse = page->objects;
                new.frozen = freelist != NULL;

        } while (!__cmpxchg_double_slab(s, page,
                freelist, counters,
                NULL, new.counters,
                "get_freelist"));

        return freelist;
}

/*
 * Slow path. The lockless freelist is empty or we need to perform
 * debugging duties.
 *
 * Processing is still very fast if new objects have been freed to the
 * regular freelist. In that case we simply take over the regular freelist
 * as the lockless freelist and zap the regular freelist.
 *
 * If that is not working then we fall back to the partial lists. We take the
 * first element of the freelist as the object to allocate now and move the
 * rest of the freelist to the lockless freelist.
 *
 * And if we were unable to get a new slab from the partial slab lists then
 * we need to allocate a new slab. This is the slowest path since it involves
 * a call to the page allocator and the setup of a new slab.
 *
 * Version of __slab_alloc to use when we know that interrupts are
 * already disabled (which is the case for bulk allocation).
 */
static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
                          unsigned long addr, struct kmem_cache_cpu *c)
{
        void *freelist;
        struct page *page;

        page = c->page;
        if (!page)
                goto new_slab;
redo:

        if (unlikely(!node_match(page, node))) {
                int searchnode = node;

                if (node != NUMA_NO_NODE && !node_present_pages(node))
                        searchnode = node_to_mem_node(node);

                if (unlikely(!node_match(page, searchnode))) {
                        stat(s, ALLOC_NODE_MISMATCH);
                        deactivate_slab(s, page, c->freelist);
                        c->page = NULL;
                        c->freelist = NULL;
                        goto new_slab;
                }
        }

        /*
         * By rights, we should be searching for a slab page that was
         * PFMEMALLOC but right now, we are losing the pfmemalloc
         * information when the page leaves the per-cpu allocator
         */
        if (unlikely(!pfmemalloc_match(page, gfpflags))) {
                deactivate_slab(s, page, c->freelist);
                c->page = NULL;
                c->freelist = NULL;
                goto new_slab;
        }

        /* must check again c->freelist in case of cpu migration or IRQ */
        freelist = c->freelist;
        if (freelist)
                goto load_freelist;

        stat(s, ALLOC_SLOWPATH);

        freelist = get_freelist(s, page);

        if (!freelist) {
                c->page = NULL;
                stat(s, DEACTIVATE_BYPASS);
                goto new_slab;
        }

        stat(s, ALLOC_REFILL);

load_freelist:
        /*
         * freelist is pointing to the list of objects to be used.
         * page is pointing to the page from which the objects are obtained.
         * That page must be frozen for per cpu allocations to work.
         */
        VM_BUG_ON(!c->page->frozen);
        c->freelist = get_freepointer(s, freelist);
        c->tid = next_tid(c->tid);
        return freelist;

new_slab:

        if (c->partial) {
                page = c->page = c->partial;
                c->partial = page->next;
                stat(s, CPU_PARTIAL_ALLOC);
                c->freelist = NULL;
                goto redo;
        }

        freelist = new_slab_objects(s, gfpflags, node, &c);

        if (unlikely(!freelist)) {
                if (!(gfpflags & __GFP_NOWARN) && printk_ratelimit())
                        slab_out_of_memory(s, gfpflags, node);
                return NULL;
        }

        page = c->page;
        if (likely(!kmem_cache_debug(s) && pfmemalloc_match(page, gfpflags)))
                goto load_freelist;

        /* Only entered in the debug case */
        if (kmem_cache_debug(s) && !alloc_debug_processing(s, page, freelist, addr))
                goto new_slab;  /* Slab failed checks. Next slab needed */

        deactivate_slab(s, page, get_freepointer(s, freelist));
        c->page = NULL;
        c->freelist = NULL;
        return freelist;
}

/*
 * Another one that disabled interrupt and compensates for possible
 * cpu changes by refetching the per cpu area pointer.
 */
static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
                          unsigned long addr, struct kmem_cache_cpu *c)
{
        void *p;
        unsigned long flags;

        local_irq_save(flags);
#ifdef CONFIG_PREEMPT
        /*
         * We may have been preempted and rescheduled on a different
         * cpu before disabling interrupts. Need to reload cpu area
         * pointer.
         */
        c = this_cpu_ptr(s->cpu_slab);
#endif

        p = ___slab_alloc(s, gfpflags, node, addr, c);
        local_irq_restore(flags);
        return p;
}

/*
 * Inlined fastpath so that allocation functions (kmalloc, kmem_cache_alloc)
 * have the fastpath folded into their functions. So no function call
 * overhead for requests that can be satisfied on the fastpath.
 *
 * The fastpath works by first checking if the lockless freelist can be used.
 * If not then __slab_alloc is called for slow processing.
 *
 * Otherwise we can simply pick the next object from the lockless free list.
 */
static __always_inline void *slab_alloc_node(struct kmem_cache *s,
                gfp_t gfpflags, int node, unsigned long addr)
{
        void *object;
        struct kmem_cache_cpu *c;
        struct page *page;
        unsigned long tid;

        if (slab_pre_alloc_hook(s, gfpflags))
                return NULL;

        s = memcg_kmem_get_cache(s, gfpflags);
redo:
        /*
         * Must read kmem_cache cpu data via this cpu ptr. Preemption is
         * enabled. We may switch back and forth between cpus while
         * reading from one cpu area. That does not matter as long
         * as we end up on the original cpu again when doing the cmpxchg.
         *
         * Preemption is disabled for the retrieval of the tid because that
         * must occur from the current processor. We cannot allow rescheduling
         * on a different processor between the determination of the pointer
         * and the retrieval of the tid.
         */
        preempt_disable();
        c = this_cpu_ptr(s->cpu_slab);

        /*
         * The transaction ids are globally unique per cpu and per operation on
         * a per cpu queue. Thus they can be guarantee that the cmpxchg_double
         * occurs on the right processor and that there was no operation on the
         * linked list in between.
         */
        tid = c->tid;
        preempt_enable();

        object = c->freelist;
        page = c->page;
        if (unlikely(!object || !node_match(page, node)))
                object = __slab_alloc(s, gfpflags, node, addr, c);

        else {
                void *next_object = get_freepointer_safe(s, object);

                /*
                 * The cmpxchg will only match if there was no additional
                 * operation and if we are on the right processor.
                 *
                 * The cmpxchg does the following atomically (without lock semantics!)
                 * 1. Relocate first pointer to the current per cpu area.
                 * 2. Verify that tid and freelist have not been changed
                 * 3. If they were not changed replace tid and freelist
                 *
                 * Since this is without lock semantics the protection is only against
                 * code executing on this cpu *not* from access by other cpus.
                 */
                if (unlikely(!this_cpu_cmpxchg_double(
                                s->cpu_slab->freelist, s->cpu_slab->tid,
                                object, tid,
                                next_object, next_tid(tid)))) {

                        note_cmpxchg_failure("slab_alloc", s, tid);
                        goto redo;
                }
                prefetch_freepointer(s, next_object);
                stat(s, ALLOC_FASTPATH);
        }

        if (unlikely(gfpflags & __GFP_ZERO) && object)
                memset(object, 0, s->object_size);

        slab_post_alloc_hook(s, gfpflags, 1, &object);

        return object;
}

static __always_inline void *slab_alloc(struct kmem_cache *s,
                gfp_t gfpflags, unsigned long addr)
{
        return slab_alloc_node(s, gfpflags, NUMA_NO_NODE, addr);
}

void *kmem_cache_alloc(struct kmem_cache *s, gfp_t gfpflags)
{
        void *ret = slab_alloc(s, gfpflags, _RET_IP_);

        trace_kmem_cache_alloc(_RET_IP_, ret, s->object_size, s->size, gfpflags);

        return ret;
}
EXPORT_SYMBOL(kmem_cache_alloc);

#ifdef CONFIG_TRACING
void *kmem_cache_alloc_trace(struct kmem_cache *s, gfp_t gfpflags, size_t size)
{
        void *ret = slab_alloc(s, gfpflags, _RET_IP_);
        trace_kmalloc(_RET_IP_, ret, size, s->size, gfpflags);
        return ret;
}
EXPORT_SYMBOL(kmem_cache_alloc_trace);

void *kmalloc_order_trace(size_t size, gfp_t flags, unsigned int order)
{
        void *ret = kmalloc_order(size, flags, order);
        trace_kmalloc(_RET_IP_, ret, size, PAGE_SIZE << order, flags);
        return ret;
}
EXPORT_SYMBOL(kmalloc_order_trace);
#endif

#ifdef CONFIG_NUMA
void *kmem_cache_alloc_node(struct kmem_cache *s, gfp_t gfpflags, int node)
{
        void *ret = slab_alloc_node(s, gfpflags, node, _RET_IP_);

        trace_kmem_cache_alloc_node(_RET_IP_, ret,
                                    s->object_size, s->size, gfpflags, node);

        return ret;
}
EXPORT_SYMBOL(kmem_cache_alloc_node);

#ifdef CONFIG_TRACING
void *kmem_cache_alloc_node_trace(struct kmem_cache *s,
                                    gfp_t gfpflags,
                                    int node, size_t size)
{
        void *ret = slab_alloc_node(s, gfpflags, node, _RET_IP_);

        trace_kmalloc_node(_RET_IP_, ret,
                           size, s->size, gfpflags, node);
        return ret;
}
EXPORT_SYMBOL(kmem_cache_alloc_node_trace);
#endif
#endif

/*
 * Slow patch handling. This may still be called frequently since objects
 * have a longer lifetime than the cpu slabs in most processing loads.
 *
 * So we still attempt to reduce cache line usage. Just take the slab
 * lock and free the item. If there is no additional partial page
 * handling required then we can return immediately.
 */
static void __slab_free(struct kmem_cache *s, struct page *page,
                        void *head, void *tail, int cnt,
                        unsigned long addr)

{
        void *prior;
        int was_frozen;
        struct page new;
        unsigned long counters;
        struct kmem_cache_node *n = NULL;
        unsigned long uninitialized_var(flags);

        stat(s, FREE_SLOWPATH);

        if (kmem_cache_debug(s) &&
            !free_debug_processing(s, page, head, tail, cnt, addr))
                return;

        do {
                if (unlikely(n)) {
                        spin_unlock_irqrestore(&n->list_lock, flags);
                        n = NULL;
                }
                prior = page->freelist;
                counters = page->counters;
                set_freepointer(s, tail, prior);
                new.counters = counters;
                was_frozen = new.frozen;
                new.inuse -= cnt;
                if ((!new.inuse || !prior) && !was_frozen) {

                        if (!kmem_cache_debug(s) && !prior)

                                /*
                                 * Slab was on no list before and will be partially empty
                                 * We can defer the list move and instead freeze it.
                                 */
                                new.frozen = 1;

                        else { /* Needs to be taken off a list */

                                n = get_node(s, page_to_nid(page));
                                /*
                                 * Speculatively acquire the list_lock.
                                 * If the cmpxchg does not succeed then we may
                                 * drop the list_lock without any processing.
                                 *
                                 * Otherwise the list_lock will synchronize with
                                 * other processors updating the list of slabs.
                                 */
                                spin_lock_irqsave(&n->list_lock, flags);

                        }
                }

        } while (!cmpxchg_double_slab(s, page,
                prior, counters,
                head, new.counters,
                "__slab_free"));

        if (likely(!n)) {

                /*
                 * If we just froze the page then put it onto the
                 * per cpu partial list.
                 */
                if (new.frozen && !was_frozen) {
                        put_cpu_partial(s, page, 1);
                        stat(s, CPU_PARTIAL_FREE);
                }
                /*
                 * The list lock was not taken therefore no list
                 * activity can be necessary.
                 */
                if (was_frozen)
                        stat(s, FREE_FROZEN);
                return;
        }

        if (unlikely(!new.inuse && n->nr_partial > s->min_partial))
                goto slab_empty;

        /*
         * Objects left in the slab. If it was not on the partial list before
         * then add it.
         */
        if (kmem_cache_debug(s) && unlikely(!prior)) {
                remove_full(s, page);
                add_partial(n, page, DEACTIVATE_TO_TAIL);
                stat(s, FREE_ADD_PARTIAL);
        }
        spin_unlock_irqrestore(&n->list_lock, flags);
        return;

slab_empty:
        if (prior) {
                /*
                 * Slab on the partial list.
                 */
                remove_partial(n, page);
                stat(s, FREE_REMOVE_PARTIAL);
        } else
                /* Slab must be on the full list */
                remove_full(s, page);

        spin_unlock_irqrestore(&n->list_lock, flags);
        stat(s, FREE_SLAB);
        discard_slab(s, page);
}

/*
 * Fastpath with forced inlining to produce a kfree and kmem_cache_free that
 * can perform fastpath freeing without additional function calls.
 *
 * The fastpath is only possible if we are freeing to the current cpu slab
 * of this processor. This typically the case if we have just allocated
 * the item before.
 *
 * If fastpath is not possible then fall back to __slab_free where we deal
 * with all sorts of special processing.
 *
 * Bulk free of a freelist with several objects (all pointing to the
 * same page) possible by specifying head and tail ptr, plus objects
 * count (cnt). Bulk free indicated by tail pointer being set.
 */
static __always_inline void slab_free(struct kmem_cache *s, struct page *page,
                                      void *head, void *tail, int cnt,
                                      unsigned long addr)
{
        void *tail_obj = tail ? : head;
        struct kmem_cache_cpu *c;
        unsigned long tid;

        slab_free_freelist_hook(s, head, tail);

redo:
        /*
         * Determine the currently cpus per cpu slab.
         * The cpu may change afterward. However that does not matter since
         * data is retrieved via this pointer. If we are on the same cpu
         * during the cmpxchg then the free will succedd.
         */
        preempt_disable();
        c = this_cpu_ptr(s->cpu_slab);

        tid = c->tid;
        preempt_enable();

        if (likely(page == c->page)) {
                set_freepointer(s, tail_obj, c->freelist);

                if (unlikely(!this_cpu_cmpxchg_double(
                                s->cpu_slab->freelist, s->cpu_slab->tid,
                                c->freelist, tid,
                                head, next_tid(tid)))) {

                        note_cmpxchg_failure("slab_free", s, tid);
                        goto redo;
                }
                stat(s, FREE_FASTPATH);
        } else
                __slab_free(s, page, head, tail_obj, cnt, addr);

}

void kmem_cache_free(struct kmem_cache *s, void *x)
{
        s = cache_from_obj(s, x);
        if (!s)
                return;
        slab_free(s, virt_to_head_page(x), x, NULL, 1, _RET_IP_);
        trace_kmem_cache_free(_RET_IP_, x);
}
EXPORT_SYMBOL(kmem_cache_free);

struct detached_freelist {
        struct page *page;
        void *tail;
        void *freelist;
        int cnt;
        struct kmem_cache *s;
};

/*
 * This function progressively scans the array with free objects (with
 * a limited look ahead) and extract objects belonging to the same
 * page.  It builds a detached freelist directly within the given
 * page/objects.  This can happen without any need for
 * synchronization, because the objects are owned by running process.
 * The freelist is build up as a single linked list in the objects.
 * The idea is, that this detached freelist can then be bulk
 * transferred to the real freelist(s), but only requiring a single
 * synchronization primitive.  Look ahead in the array is limited due
 * to performance reasons.
 */
static inline
int build_detached_freelist(struct kmem_cache *s, size_t size,
                            void **p, struct detached_freelist *df)
{
        size_t first_skipped_index = 0;
        int lookahead = 3;
        void *object;

        /* Always re-init detached_freelist */
        df->page = NULL;

        do {
                object = p[--size];
        } while (!object && size);

        if (!object)
                return 0;

        /* Support for memcg, compiler can optimize this out */
        df->s = cache_from_obj(s, object);

        /* Start new detached freelist */
        set_freepointer(df->s, object, NULL);
        df->page = virt_to_head_page(object);
        df->tail = object;
        df->freelist = object;
        p[size] = NULL; /* mark object processed */
        df->cnt = 1;

        while (size) {
                object = p[--size];
                if (!object)
                        continue; /* Skip processed objects */

                /* df->page is always set at this point */
                if (df->page == virt_to_head_page(object)) {
                        /* Opportunity build freelist */
                        set_freepointer(df->s, object, df->freelist);
                        df->freelist = object;
                        df->cnt++;
                        p[size] = NULL; /* mark object processed */

                        continue;
                }

                /* Limit look ahead search */
                if (!--lookahead)
                        break;

                if (!first_skipped_index)
                        first_skipped_index = size + 1;
        }

        return first_skipped_index;
}

/* Note that interrupts must be enabled when calling this function. */
void kmem_cache_free_bulk(struct kmem_cache *s, size_t size, void **p)
{
        if (WARN_ON(!size))
                return;

        do {
                struct detached_freelist df;

                size = build_detached_freelist(s, size, p, &df);
                if (unlikely(!df.page))
                        continue;

                slab_free(df.s, df.page, df.freelist, df.tail, df.cnt,_RET_IP_);
        } while (likely(size));
}
EXPORT_SYMBOL(kmem_cache_free_bulk);

/* Note that interrupts must be enabled when calling this function. */
int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
                          void **p)
{
        struct kmem_cache_cpu *c;
        int i;

        /* memcg and kmem_cache debug support */
        if (unlikely(slab_pre_alloc_hook(s, flags)))
                return false;
        /*
         * Drain objects in the per cpu slab, while disabling local
         * IRQs, which protects against PREEMPT and interrupts
         * handlers invoking normal fastpath.
         */
        local_irq_disable();
        c = this_cpu_ptr(s->cpu_slab);

        for (i = 0; i < size; i++) {
                void *object = c->freelist;

                if (unlikely(!object)) {
                        /*
                         * Invoking slow path likely have side-effect
                         * of re-populating per CPU c->freelist
                         */
                        p[i] = ___slab_alloc(s, flags, NUMA_NO_NODE,
                                            _RET_IP_, c);
                        if (unlikely(!p[i]))
                                goto error;

                        c = this_cpu_ptr(s->cpu_slab);
                        continue; /* goto for-loop */
                }
                c->freelist = get_freepointer(s, object);
                p[i] = object;
        }
        c->tid = next_tid(c->tid);
        local_irq_enable();

        /* Clear memory outside IRQ disabled fastpath loop */
        if (unlikely(flags & __GFP_ZERO)) {
                int j;

                for (j = 0; j < i; j++)
                        memset(p[j], 0, s->object_size);
        }