linux-kernel - Re: "slab: Fix missing DEBUG

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Date:	Tue, 8 Feb 2011 09:02:09 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Russell King <rmk@....linux.org.uk>
cc:	Pekka Enberg <penberg@...nel.org>,
	Shiyong Li <shi-yong.li@...orola.com>,
	Linux Kernel List <linux-kernel@...r.kernel.org>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: "slab: Fix missing DEBUG_SLAB last user" breaks ARM

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) ...

?


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