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

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Message-Id: <20080728133504.156f438f.akpm@linux-foundation.org>
Date:	Mon, 28 Jul 2008 13:35:04 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	linux-kernel@...r.kernel.org, mhalcrow@...ibm.com,
	stable@...nel.org
Subject: Re: [PATCH] eCryptfs - use page_alloc not kmalloc to get a page of
 memory

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.

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