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    SubjectRe: [PATCH] slub: always align cpu_slab to honor cmpxchg_double requirement
    On 6/2/2011 1:16 PM, David Rientjes wrote:
    > On Thu, 2 Jun 2011, Chris Metcalf wrote:
    >> On an architecture without CMPXCHG_LOCAL but with DEBUG_VM enabled,
    >> the VM_BUG_ON() in __pcpu_double_call_return_bool() will cause an early
    >> panic during boot unless we always align cpu_slab properly.
    >> In principle we could remove the alignment-testing VM_BUG_ON() for
    >> architectures that don't have CMPXCHG_LOCAL, but leaving it in means
    >> that new code will tend not to break x86 even if it is introduced
    >> on another platform, and it's low cost to require alignment.
    >> Signed-off-by: Chris Metcalf <>
    > Acked-by: David Rientjes <>
    >> ---
    >> This needs to be pushed for 3.0 to allow arch/tile to boot.
    >> I'm happy to push it but I assume it would be better coming
    >> from an mm or percpu tree. Thanks!
    > Should also be marked for stable for 2.6.39.x, right?

    No, in 2.6.39 the irqsafe_cpu_cmpxchg_double() was guarded under "#ifdef
    CONFIG_CMPXCHG_LOCAL". Now it's not. I suppose we could take the comment
    change in percpu.h for 2.6.39, but it probably doesn't merit churning the
    stable tree.

    Chris Metcalf, Tilera Corp.

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