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    Subject[patch 03/26] Slab allocators: Consistent ZERO_SIZE_PTR support and NULL result semantics
    Define ZERO_OR_NULL_PTR macro to be able to remove the checks
    from the allocators. Move ZERO_SIZE_PTR related stuff into slab.h.

    Make ZERO_SIZE_PTR work for all slab allocators and get rid of the
    WARN_ON_ONCE(size == 0) that is still remaining in SLAB.

    Make slub return NULL like the other allocators if a too large
    memory segment is requested via __kmalloc.

    Signed-off-by: Christoph Lameter <clameter@sgi.com>

    ---
    include/linux/slab.h | 13 +++++++++++++
    include/linux/slab_def.h | 12 ++++++++++++
    include/linux/slub_def.h | 11 -----------
    mm/slab.c | 14 ++++++++------
    mm/slob.c | 13 ++++++++-----
    mm/slub.c | 29 ++++++++++++++++-------------
    mm/util.c | 2 +-
    7 files changed, 58 insertions(+), 36 deletions(-)

    Index: linux-2.6.22-rc4-mm2/include/linux/slab.h
    ===================================================================
    --- linux-2.6.22-rc4-mm2.orig/include/linux/slab.h 2007-06-12 12:04:57.000000000 -0700
    +++ linux-2.6.22-rc4-mm2/include/linux/slab.h 2007-06-17 20:35:03.000000000 -0700
    @@ -33,6 +33,19 @@
    #define SLAB_RECLAIM_ACCOUNT 0x00020000UL /* Objects are reclaimable */
    #define SLAB_TEMPORARY SLAB_RECLAIM_ACCOUNT /* Objects are short-lived */
    /*
    + * ZERO_SIZE_PTR will be returned for zero sized kmalloc requests.
    + *
    + * Dereferencing ZERO_SIZE_PTR will lead to a distinct access fault.
    + *
    + * ZERO_SIZE_PTR can be passed to kfree though in the same way that NULL can.
    + * Both make kfree a no-op.
    + */
    +#define ZERO_SIZE_PTR ((void *)16)
    +
    +#define ZERO_OR_NULL_PTR(x) ((unsigned long)(x) < \
    + (unsigned long)ZERO_SIZE_PTR)
    +
    +/*
    * struct kmem_cache related prototypes
    */
    void __init kmem_cache_init(void);
    Index: linux-2.6.22-rc4-mm2/include/linux/slab_def.h
    ===================================================================
    --- linux-2.6.22-rc4-mm2.orig/include/linux/slab_def.h 2007-06-04 17:57:25.000000000 -0700
    +++ linux-2.6.22-rc4-mm2/include/linux/slab_def.h 2007-06-17 20:35:03.000000000 -0700
    @@ -29,6 +29,10 @@ static inline void *kmalloc(size_t size,
    {
    if (__builtin_constant_p(size)) {
    int i = 0;
    +
    + if (!size)
    + return ZERO_SIZE_PTR;
    +
    #define CACHE(x) \
    if (size <= x) \
    goto found; \
    @@ -55,6 +59,10 @@ static inline void *kzalloc(size_t size,
    {
    if (__builtin_constant_p(size)) {
    int i = 0;
    +
    + if (!size)
    + return ZERO_SIZE_PTR;
    +
    #define CACHE(x) \
    if (size <= x) \
    goto found; \
    @@ -84,6 +92,10 @@ static inline void *kmalloc_node(size_t
    {
    if (__builtin_constant_p(size)) {
    int i = 0;
    +
    + if (!size)
    + return ZERO_SIZE_PTR;
    +
    #define CACHE(x) \
    if (size <= x) \
    goto found; \
    Index: linux-2.6.22-rc4-mm2/include/linux/slub_def.h
    ===================================================================
    --- linux-2.6.22-rc4-mm2.orig/include/linux/slub_def.h 2007-06-17 19:10:33.000000000 -0700
    +++ linux-2.6.22-rc4-mm2/include/linux/slub_def.h 2007-06-17 20:35:03.000000000 -0700
    @@ -160,17 +160,6 @@ static inline struct kmem_cache *kmalloc
    #endif


    -/*
    - * ZERO_SIZE_PTR will be returned for zero sized kmalloc requests.
    - *
    - * Dereferencing ZERO_SIZE_PTR will lead to a distinct access fault.
    - *
    - * ZERO_SIZE_PTR can be passed to kfree though in the same way that NULL can.
    - * Both make kfree a no-op.
    - */
    -#define ZERO_SIZE_PTR ((void *)16)
    -
    -
    static inline void *kmalloc(size_t size, gfp_t flags)
    {
    if (__builtin_constant_p(size) && !(flags & SLUB_DMA)) {
    Index: linux-2.6.22-rc4-mm2/mm/slab.c
    ===================================================================
    --- linux-2.6.22-rc4-mm2.orig/mm/slab.c 2007-06-17 19:10:33.000000000 -0700
    +++ linux-2.6.22-rc4-mm2/mm/slab.c 2007-06-17 20:35:08.000000000 -0700
    @@ -774,7 +774,9 @@ static inline struct kmem_cache *__find_
    */
    BUG_ON(malloc_sizes[INDEX_AC].cs_cachep == NULL);
    #endif
    - WARN_ON_ONCE(size == 0);
    + if (!size)
    + return ZERO_SIZE_PTR;
    +
    while (size > csizep->cs_size)
    csizep++;

    @@ -2340,7 +2342,7 @@ kmem_cache_create (const char *name, siz
    * this should not happen at all.
    * But leave a BUG_ON for some lucky dude.
    */
    - BUG_ON(!cachep->slabp_cache);
    + BUG_ON(ZERO_OR_NULL_PTR(cachep->slabp_cache));
    }
    cachep->ctor = ctor;
    cachep->name = name;
    @@ -3642,8 +3644,8 @@ __do_kmalloc_node(size_t size, gfp_t fla
    struct kmem_cache *cachep;

    cachep = kmem_find_general_cachep(size, flags);
    - if (unlikely(cachep == NULL))
    - return NULL;
    + if (unlikely(ZERO_OR_NULL_PTR(cachep)))
    + return cachep;
    return kmem_cache_alloc_node(cachep, flags, node);
    }

    @@ -3749,7 +3751,7 @@ void kfree(const void *objp)
    struct kmem_cache *c;
    unsigned long flags;

    - if (unlikely(!objp))
    + if (unlikely(ZERO_OR_NULL_PTR(objp)))
    return;
    local_irq_save(flags);
    kfree_debugcheck(objp);
    @@ -4436,7 +4438,7 @@ const struct seq_operations slabstats_op
    */
    size_t ksize(const void *objp)
    {
    - if (unlikely(objp == NULL))
    + if (unlikely(ZERO_OR_NULL_PTR(objp)))
    return 0;

    return obj_size(virt_to_cache(objp));
    Index: linux-2.6.22-rc4-mm2/mm/slob.c
    ===================================================================
    --- linux-2.6.22-rc4-mm2.orig/mm/slob.c 2007-06-17 19:10:33.000000000 -0700
    +++ linux-2.6.22-rc4-mm2/mm/slob.c 2007-06-17 20:35:04.000000000 -0700
    @@ -306,7 +306,7 @@ static void slob_free(void *block, int s
    slobidx_t units;
    unsigned long flags;

    - if (!block)
    + if (ZERO_OR_NULL_PTR(block))
    return;
    BUG_ON(!size);

    @@ -384,11 +384,14 @@ out:

    void *__kmalloc(size_t size, gfp_t gfp)
    {
    + unsigned int *m;
    int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);

    if (size < PAGE_SIZE - align) {
    - unsigned int *m;
    - m = slob_alloc(size + align, gfp, align);
    + if (!size)
    + return ZERO_SIZE_PTR;
    +
    + m = slob_alloc(size + align, gfp, align);
    if (m)
    *m = size;
    return (void *)m + align;
    @@ -411,7 +414,7 @@ void kfree(const void *block)
    {
    struct slob_page *sp;

    - if (!block)
    + if (ZERO_OR_NULL_PTR(block))
    return;

    sp = (struct slob_page *)virt_to_page(block);
    @@ -430,7 +433,7 @@ size_t ksize(const void *block)
    {
    struct slob_page *sp;

    - if (!block)
    + if (ZERO_OR_NULL_PTR(block))
    return 0;

    sp = (struct slob_page *)virt_to_page(block);
    Index: linux-2.6.22-rc4-mm2/mm/util.c
    ===================================================================
    --- linux-2.6.22-rc4-mm2.orig/mm/util.c 2007-06-17 19:10:33.000000000 -0700
    +++ linux-2.6.22-rc4-mm2/mm/util.c 2007-06-17 20:35:03.000000000 -0700
    @@ -99,7 +99,7 @@ void *krealloc(const void *p, size_t new

    if (unlikely(!new_size)) {
    kfree(p);
    - return NULL;
    + return ZERO_SIZE_PTR;
    }

    ks = ksize(p);
    Index: linux-2.6.22-rc4-mm2/mm/slub.c
    ===================================================================
    --- linux-2.6.22-rc4-mm2.orig/mm/slub.c 2007-06-17 19:10:33.000000000 -0700
    +++ linux-2.6.22-rc4-mm2/mm/slub.c 2007-06-17 20:35:04.000000000 -0700
    @@ -2279,10 +2279,11 @@ static struct kmem_cache *get_slab(size_
    int index = kmalloc_index(size);

    if (!index)
    - return NULL;
    + return ZERO_SIZE_PTR;

    /* Allocation too large? */
    - BUG_ON(index < 0);
    + if (index < 0)
    + return NULL;

    #ifdef CONFIG_ZONE_DMA
    if ((flags & SLUB_DMA)) {
    @@ -2323,9 +2324,10 @@ void *__kmalloc(size_t size, gfp_t flags
    {
    struct kmem_cache *s = get_slab(size, flags);

    - if (s)
    - return slab_alloc(s, flags, -1, __builtin_return_address(0));
    - return ZERO_SIZE_PTR;
    + if (ZERO_OR_NULL_PTR(s))
    + return s;
    +
    + return slab_alloc(s, flags, -1, __builtin_return_address(0));
    }
    EXPORT_SYMBOL(__kmalloc);

    @@ -2334,9 +2336,10 @@ void *__kmalloc_node(size_t size, gfp_t
    {
    struct kmem_cache *s = get_slab(size, flags);

    - if (s)
    - return slab_alloc(s, flags, node, __builtin_return_address(0));
    - return ZERO_SIZE_PTR;
    + if (ZERO_OR_NULL_PTR(s))
    + return s;
    +
    + return slab_alloc(s, flags, node, __builtin_return_address(0));
    }
    EXPORT_SYMBOL(__kmalloc_node);
    #endif
    @@ -2387,7 +2390,7 @@ void kfree(const void *x)
    * this comparison would be true for all "negative" pointers
    * (which would cover the whole upper half of the address space).
    */
    - if ((unsigned long)x <= (unsigned long)ZERO_SIZE_PTR)
    + if (ZERO_OR_NULL_PTR(x))
    return;

    page = virt_to_head_page(x);
    @@ -2706,8 +2709,8 @@ void *__kmalloc_track_caller(size_t size
    {
    struct kmem_cache *s = get_slab(size, gfpflags);

    - if (!s)
    - return ZERO_SIZE_PTR;
    + if (ZERO_OR_NULL_PTR(s))
    + return s;

    return slab_alloc(s, gfpflags, -1, caller);
    }
    @@ -2717,8 +2720,8 @@ void *__kmalloc_node_track_caller(size_t
    {
    struct kmem_cache *s = get_slab(size, gfpflags);

    - if (!s)
    - return ZERO_SIZE_PTR;
    + if (ZERO_OR_NULL_PTR(s))
    + return s;

    return slab_alloc(s, gfpflags, node, caller);
    }
    --
    -
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