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Re: Help debugging a use after free

To: Stuart MENEFY <stuart.menefy@xxxxxx>
Subject: Re: Help debugging a use after free
From: Russell Cattelan <cattelan@xxxxxxxxxxx>
Date: Thu, 23 Apr 2009 11:24:49 -0500
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, Russell Cattelan <cattelan@xxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <49F092D6.4070507@xxxxxx>
References: <49E37972.1070101@xxxxxx> <49E4DF8C.4050800@xxxxxxxxxxx> <49E8A081.7020200@xxxxxx> <20090419081702.GD16929@xxxxxxxxxxxxxxxx> <49F092D6.4070507@xxxxxx>
User-agent: Thunderbird (Macintosh/20070728)
Stuart MENEFY wrote:
> Dave Chinner wrote:
>> On Fri, Apr 17, 2009 at 04:30:09PM +0100, Stuart MENEFY wrote:
>>>> If you can instrument actually free that is causing the problem it
>>>> would be good to print out the
>>>> actually pid doing the free and as many return addresses that you can,
>>>> so we can get an
>>>> idea of the actual call chain.
>>> The free is coming from the xfssyncd thread, the back trace looks like:
>>> [<8418d0e2>] xfs_idestroy+0x22/0x100
>>> [<8418a1b0>] xfs_ireclaim+0x50/0x80
>>> [<841ad7f2>] xfs_finish_reclaim+0x32/0x1c0
>>> [<841ada30>] xfs_finish_reclaim_all+0xb0/0x100
>>> [<8418a780>] xfs_ilock_nowait+0x0/0x160
>>> [<841a9df2>] xfs_syncsub+0x52/0x360
>>> [<84335108>] schedule_timeout+0x48/0x100
>>> [<841ab684>] xfs_sync+0x24/0x40
>>> [<841e0ce0>] list_add+0x0/0x20
>>> [<841c041c>] vfs_sync+0x1c/0x40
>>> [<841bf37c>] vfs_sync_worker+0x1c/0x60
>>> [<841bf6b6>] xfssyncd+0xb6/0x140
>>> [<8402f0dc>] kthread+0x3c/0x80
>>> [<84012440>] complete+0x0/0x60
>>> [<841bf600>] xfssyncd+0x0/0x140
>>> [<8402f060>] kthread_should_stop+0x0/0x20
>>> [<84003984>] kernel_thread_helper+0x4/0x20
>>> [<8402f0a0>] kthread+0x0/0x80
>>> [<84003980>] kernel_thread_helper+0x0/0x20
>> There were some use-after-free fixes in .27 timeframe to the inode
>> reclaim code. Can you reeetest with a more recent kernel?
> Possibly. I have a half-finished port of 2.6.27-rc4
>  to our hardware
> which I could probably get going fairly quickly. Do you think that
> would be sufficient to pick up the use-after-free fixes?
> Thanks
> Stuart
Any reason you are using an rc4? vs 2.6.27?

I would simply run a diff over rc4 fs/xfs and 2.6.27 fs/xfs and see what
is different if anything.

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