Re: "slab: Fix missing DEBUG_SLAB last user" breaks ARM

[Pekka Enberg]

On Tue, Feb 8, 2011 at 5:02 PM, Christoph Lameter <cl@xxxxxxxxx> wrote:
> On Tue, 8 Feb 2011, Russell King wrote:
>
>> > I thought the fix was for ARM, actually, but unfortunately the
>> > changelog is somewhat terse (shame on me). Hmm?
>>
>> As you say, the changelog is soo terse that we now have no idea why this
>> commit was created.
>>
>> So, what's the fix here?  It looks to me like a revert is in order.
>>
>> I suggest that if it does get reverted, a copy of my original bug report
>> is included in the revert commit so that all the details are available if
>> it needs revisiting.
>
> Uhh.. That first hunk in commit 5c5e3b33b7cb959a401f823707bee006caadd76e
> looks wrong to me. ralign is usually a power of two and greater than
> alignof(unsigned long long). The & operation will result in 0 and never
> exempt any caches.
>
> diff --git a/mm/slab.c b/mm/slab.c
> index bac0f4f..525c664 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -2220,8 +2220,8 @@ kmem_cache_create (const char *name, size_t size,
> size_t align,
>        if (ralign < align) {
>                ralign = align;
>        }
> -       /* disable debug if necessary */
> -       if (ralign > __alignof__(unsigned long long))
> +       /* disable debug if not aligning with REDZONE_ALIGN */
> +       if (ralign & (__alignof__(unsigned long long) - 1))
>                flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER);
>        /*
>         * 4) Store it.
>
>
> Did you mean
>
>        if (ralign > REDZONE_ALIGN) ...
>
> ?

Ping. Any arm-capable tester out there that can verify this fix? OTOH,
since Shiyong Li hasn't showed up, I'm inclined to just revert the
commit...
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