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    SubjectRe: kfree(0) - ok?
    On Sat, 18 Aug 2007, Pekka Enberg wrote:

    > Agreed, especially as we have real zero-sized objects returned from
    > kmalloc() et al now.



    Slab allocators: Fail if ksize is called with a NULL parameter

    A NULL pointer means that the object was not allocated. One cannot
    determine the size of an object that has not been allocated. Currently
    we return 0 but we really should BUG() on attempts to determine the size
    of something nonexistent.

    krealloc() interprets NULL to mean a zero sized object. Handle that
    separately in krealloc().

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

    Index: linux-2.6/mm/slab.c
    ===================================================================
    --- linux-2.6.orig/mm/slab.c 2007-08-17 16:17:41.000000000 -0700
    +++ linux-2.6/mm/slab.c 2007-08-17 16:18:15.000000000 -0700
    @@ -4436,7 +4436,8 @@ const struct seq_operations slabstats_op
    */
    size_t ksize(const void *objp)
    {
    - if (unlikely(ZERO_OR_NULL_PTR(objp)))
    + BUG_ON(!objp);
    + if (unlikely(objp == ZERO_SIZE_PTR))
    return 0;

    return obj_size(virt_to_cache(objp));
    Index: linux-2.6/mm/slob.c
    ===================================================================
    --- linux-2.6.orig/mm/slob.c 2007-08-17 16:18:19.000000000 -0700
    +++ linux-2.6/mm/slob.c 2007-08-17 16:18:40.000000000 -0700
    @@ -484,7 +484,8 @@ size_t ksize(const void *block)
    {
    struct slob_page *sp;

    - if (ZERO_OR_NULL_PTR(block))
    + BUG_ON(!block);
    + if (block == ZERO_SIZE_PTR)
    return 0;

    sp = (struct slob_page *)virt_to_page(block);
    Index: linux-2.6/mm/slub.c
    ===================================================================
    --- linux-2.6.orig/mm/slub.c 2007-08-17 16:16:36.000000000 -0700
    +++ linux-2.6/mm/slub.c 2007-08-17 16:17:36.000000000 -0700
    @@ -2426,7 +2426,8 @@ size_t ksize(const void *object)
    struct page *page;
    struct kmem_cache *s;

    - if (ZERO_OR_NULL_PTR(object))
    + BUG_ON(!object);
    + if (object == ZERO_SIZE_PTR)
    return 0;

    page = get_object_page(object);
    Index: linux-2.6/mm/util.c
    ===================================================================
    --- linux-2.6.orig/mm/util.c 2007-08-17 16:16:29.000000000 -0700
    +++ linux-2.6/mm/util.c 2007-08-17 16:16:32.000000000 -0700
    @@ -81,14 +81,16 @@ EXPORT_SYMBOL(kmemdup);
    void *krealloc(const void *p, size_t new_size, gfp_t flags)
    {
    void *ret;
    - size_t ks;
    + size_t ks = 0;

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

    - ks = ksize(p);
    + if (p)
    + ks = ksize(p);
    +
    if (ks >= new_size)
    return (void *)p;

    -
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