• David Woodhouse's avatar
    Increase slab redzone to 64bits · b46b8f19
    David Woodhouse authored
    There are two problems with the existing redzone implementation.
    Firstly, it's causing misalignment of structures which contain a 64-bit
    integer, such as netfilter's 'struct ipt_entry' -- causing netfilter
    modules to fail to load because of the misalignment.  (In particular, the
    first check in
    On ppc32 and sparc32, amongst others, __alignof__(uint64_t) == 8.
    With slab debugging, we use 32-bit redzones. And allocated slab objects
    aren't sufficiently aligned to hold a structure containing a uint64_t.
    By _just_ setting ARCH_KMALLOC_MINALIGN to __alignof__(u64) we'd disable
    redzone checks on those architectures.  By using 64-bit redzones we avoid that
    loss of debugging, and also fix the other problem while we're at it.
    When investigating this, I noticed that on 64-bit platforms we're using a
    32-bit value of RED_ACTIVE/RED_INACTIVE in the 64-bit memory location set
    aside for the redzone.  Which means that the four bytes immediately before
    or after the allocated object at 0x00,0x00,0x00,0x00 for LE and BE
    machines, respectively.  Which is probably not the most useful choice of
    poison value.
    One way to fix both of those at once is just to switch to 64-bit
    redzones in all cases.
    Signed-off-by: default avatarDavid Woodhouse <dwmw2@infradead.org>
    Acked-by: default avatarPekka Enberg <penberg@cs.helsinki.fi>
    Cc: Christoph Lameter <clameter@engr.sgi.com>
    Acked-by: default avatarDavid S. Miller <davem@davemloft.net>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>