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    Subject[PATCH] [264/275] Revert "slab: Fix missing DEBUG_SLAB last user"
    Date
    2.6.35-longterm review patch.  If anyone has any objections, please let me know.

    ------------------
    From: Pekka Enberg <penberg@kernel.org>

    [ upstream commit 3ff84a7f36554b257cd57325b1a7c1fa4b49fbe3 ]

    This reverts commit 5c5e3b33b7cb959a401f823707bee006caadd76e.

    The commit breaks ARM thusly:

    | Mount-cache hash table entries: 512
    | slab error in verify_redzone_free(): cache `idr_layer_cache': memory outside object was overwritten
    | Backtrace:
    | [<c0227088>] (dump_backtrace+0x0/0x110) from [<c0431afc>] (dump_stack+0x18/0x1c)
    | [<c0431ae4>] (dump_stack+0x0/0x1c) from [<c0293304>] (__slab_error+0x28/0x30)
    | [<c02932dc>] (__slab_error+0x0/0x30) from [<c0293a74>] (cache_free_debugcheck+0x1c0/0x2b8)
    | [<c02938b4>] (cache_free_debugcheck+0x0/0x2b8) from [<c0293f78>] (kmem_cache_free+0x3c/0xc0)
    | [<c0293f3c>] (kmem_cache_free+0x0/0xc0) from [<c032b1c8>] (ida_get_new_above+0x19c/0x1c0)
    | [<c032b02c>] (ida_get_new_above+0x0/0x1c0) from [<c02af7ec>] (alloc_vfsmnt+0x54/0x144)
    | [<c02af798>] (alloc_vfsmnt+0x0/0x144) from [<c0299830>] (vfs_kern_mount+0x30/0xec)
    | [<c0299800>] (vfs_kern_mount+0x0/0xec) from [<c0299908>] (kern_mount_data+0x1c/0x20)
    | [<c02998ec>] (kern_mount_data+0x0/0x20) from [<c02146c4>] (sysfs_init+0x68/0xc8)
    | [<c021465c>] (sysfs_init+0x0/0xc8) from [<c02137d4>] (mnt_init+0x90/0x1b0)
    | [<c0213744>] (mnt_init+0x0/0x1b0) from [<c0213388>] (vfs_caches_init+0x100/0x140)
    | [<c0213288>] (vfs_caches_init+0x0/0x140) from [<c0208c0c>] (start_kernel+0x2e8/0x368)
    | [<c0208924>] (start_kernel+0x0/0x368) from [<c0208034>] (__enable_mmu+0x0/0x2c)
    | c0113268: redzone 1:0xd84156c5c032b3ac, redzone 2:0xd84156c5635688c0.
    | slab error in cache_alloc_debugcheck_after(): cache `idr_layer_cache': double free, or memory outside object was overwritten
    | ...
    | c011307c: redzone 1:0x9f91102ffffffff, redzone 2:0x9f911029d74e35b
    | slab: Internal list corruption detected in cache 'idr_layer_cache'(24), slabp c0113000(16). Hexdump:
    |
    | 000: 20 4f 10 c0 20 4f 10 c0 7c 00 00 00 7c 30 11 c0
    | 010: 10 00 00 00 10 00 00 00 00 00 c9 17 fe ff ff ff
    | 020: fe ff ff ff fe ff ff ff fe ff ff ff fe ff ff ff
    | 030: fe ff ff ff fe ff ff ff fe ff ff ff fe ff ff ff
    | 040: fe ff ff ff fe ff ff ff fe ff ff ff fe ff ff ff
    | 050: fe ff ff ff fe ff ff ff fe ff ff ff 11 00 00 00
    | 060: 12 00 00 00 13 00 00 00 14 00 00 00 15 00 00 00
    | 070: 16 00 00 00 17 00 00 00 c0 88 56 63
    | kernel BUG at /home/rmk/git/linux-2.6-rmk/mm/slab.c:2928!

    Reference: https://lkml.org/lkml/2011/2/7/238
    Cc: <stable@kernel.org> # 2.6.35.y and later
    Reported-and-analyzed-by: Russell King <rmk@arm.linux.org.uk>
    Signed-off-by: Pekka Enberg <penberg@kernel.org>
    Signed-off-by: Andi Kleen <ak@linux.intel.com>

    ---
    mm/slab.c | 8 ++++----
    1 file changed, 4 insertions(+), 4 deletions(-)

    Index: linux-2.6.35.y/mm/slab.c
    ===================================================================
    --- linux-2.6.35.y.orig/mm/slab.c 2011-01-13 09:47:51.000000000 -0800
    +++ linux-2.6.35.y/mm/slab.c 2011-03-29 23:28:50.113636629 -0700
    @@ -2289,8 +2289,8 @@
    if (ralign < align) {
    ralign = align;
    }
    - /* disable debug if not aligning with REDZONE_ALIGN */
    - if (ralign & (__alignof__(unsigned long long) - 1))
    + /* disable debug if necessary */
    + if (ralign > __alignof__(unsigned long long))
    flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER);
    /*
    * 4) Store it.
    @@ -2316,8 +2316,8 @@
    */
    if (flags & SLAB_RED_ZONE) {
    /* add space for red zone words */
    - cachep->obj_offset += align;
    - size += align + sizeof(unsigned long long);
    + cachep->obj_offset += sizeof(unsigned long long);
    + size += 2 * sizeof(unsigned long long);
    }
    if (flags & SLAB_STORE_USER) {
    /* user store requires one word storage behind the end of

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