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Re: [PATCH] Fix use-after-free with log and quotas

To: Lachlan McIlroy <lachlan@xxxxxxx>
Subject: Re: [PATCH] Fix use-after-free with log and quotas
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 16 Sep 2008 14:08:25 +1000
Cc: xfs-dev <xfs-dev@xxxxxxx>, xfs-oss <xfs@xxxxxxxxxxx>
In-reply-to: <48CDCB04.1040402@xxxxxxx>
Mail-followup-to: Lachlan McIlroy <lachlan@xxxxxxx>, xfs-dev <xfs-dev@xxxxxxx>, xfs-oss <xfs@xxxxxxxxxxx>
References: <48CA2B23.4020405@xxxxxxx> <20080913040219.GA5811@disturbed> <48CDCB04.1040402@xxxxxxx>
User-agent: Mutt/1.5.18 (2008-05-17)
On Mon, Sep 15, 2008 at 12:40:04PM +1000, Lachlan McIlroy wrote:
> Dave Chinner wrote:
>> On Fri, Sep 12, 2008 at 06:41:07PM +1000, Lachlan McIlroy wrote:
>>> Destroying the quota stuff on unmount can access the log - ie XFS_QM_DONE()
>>> ends up in xfs_dqunlock() which calls xfs_trans_unlocked_item() and then
>>> xfs_log_move_tail().  By this time the log has already been destroyed.
>>> Just move the cleanup of the quota code earlier in xfs_unmountfs() before
>>> the call to xfs_log_unmount().  Moving XFS_QM_DONE() up near
>>> XFS_QM_DQPURGEALL() seems like a good spot.
>>
>> FWIW, has this been actually seen in the real world?
> Yes.  And easy to reproduce too.

Care to provide details about the test case, then? I can't help if
you keep me in the dark....

>> torn down the AIL and there should be no log items in the system
>> that are in the AIL....
> That should be the case but clearly not happening.  Pete is investigating
> an issue right now where a dquot is not getting removed from the AIL when
> it should.  Until we've got to the bottom of that problem I'd prefer to at
> least avoid this use after free issue.

No point in putting a bandaid in if you're already in the process of
trying to find the real cause....

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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