linux-kernel - Re: VM: Fix nasty and subtle race in shared mmap'ed page writeback

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Date:	Sun, 31 Dec 2006 14:55:58 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Andrea Gelmini <gelma@...ma.net>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: VM: Fix nasty and subtle race in shared mmap'ed page writeback

Andrea Gelmini wrote:
> On Fri, Dec 29, 2006 at 06:59:02PM +0000, Linux Kernel Mailing List wrote:
> 
>>Gitweb:     http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=7658cc289288b8ae7dd2c2224549a048431222b3
>>Commit:     7658cc289288b8ae7dd2c2224549a048431222b3
>>Parent:     3bf8ba38f38d3647368e4edcf7d019f9f8d9184a
>>Author:     Linus Torvalds <torvalds@...mini.osdl.org>
>>AuthorDate: Fri Dec 29 10:00:58 2006 -0800
>>Committer:  Linus Torvalds <torvalds@...mini.osdl.org>
>>CommitDate: Fri Dec 29 10:00:58 2006 -0800
>>
>>    VM: Fix nasty and subtle race in shared mmap'ed page writeback
> 
> 
> With 2.6.20-rc2-git1, which contain this patch, I have no more Berkeley
> DB corruption with Klibido.
> I'm afraid a lot of software project switched to Sqlite, from BDB,
> because the bug this patch fix (ie. http://bogofilter.sourceforge.net/).
> I've also thought, since years, it was an userland problem.

This bug was only introduced in 2.6.19, due to a change that caused pte
dirty bits to be discarded without a subsequent set_page_dirty() (nowhere
else in the kernel should have done this).

So if your corruption is years old, then it must be something else.
Maybe it is hidden by a timing change, or BDB isn't using msync properly.

-- 
SUSE Labs, Novell Inc.
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