linux-kernel - Re: [PATCH] eCryptfs - use page_alloc not kmalloc to get a page of memory

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Message-ID: <84144f020807281342t2e1a3dc3id01314ac01de406f@mail.gmail.com>
Date:	Mon, 28 Jul 2008 23:42:37 +0300
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	"Eric Sandeen" <sandeen@...hat.com>, linux-kernel@...r.kernel.org,
	mhalcrow@...ibm.com, stable@...nel.org,
	"Christoph Lameter" <cl@...ux-foundation.org>
Subject: Re: [PATCH] eCryptfs - use page_alloc not kmalloc to get a page of memory

On Mon, Jul 28, 2008 at 11:35 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Mon, 28 Jul 2008 11:13:03 -0500
> Eric Sandeen <sandeen@...hat.com> wrote:
>
>> With SLUB debugging turned on in 2.6.26, I was getting memory corruption
>> when testing eCryptfs.  The root cause turned out to be that eCryptfs
>> was doing kmalloc(PAGE_CACHE_SIZE); virt_to_page() and treating that
>> as a nice page-aligned chunk of memory.  But at least with SLUB debugging
>> on, this is not always true, and the page we get from virt_to_page does
>> not necessarily match the PAGE_CACHE_SIZE worth of memory we got from
>> kmalloc.
>>
>> My simple testcase was 2 loops doing "rm -f fileX; cp /tmp/fileX ." for
>> 2 different multi-megabyte files.  With this change I no longer see
>> the corruption.
>
> The fix applies to both 2.6.25 and to 2.6.26 and appears to be needed
> in both kernel versions, so I have tagged it for backporting into both.

Hmm, SLUB will use the page allocator directly for PAGE_CACHE_SIZE
regadless of whether debugging is enabled or not...
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