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Re: XFS reclaim lock order bug

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: XFS reclaim lock order bug
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Thu, 25 Nov 2010 12:37:37 +0100
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Nick Piggin <npiggin@xxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <20101125112530.GB4195@xxxxxxxxxxxxx>
References: <20101123121802.GA4785@amd> <20101123211258.GY22876@dastard> <20101124200341.GA2493@xxxxxxxxxxxxx> <20101125034824.GA3359@amd> <1290666325.2072.535.camel@laptop> <20101125102940.GE12187@dastard> <20101125112530.GB4195@xxxxxxxxxxxxx>
On Thu, 2010-11-25 at 06:25 -0500, Christoph Hellwig wrote:
> On Thu, Nov 25, 2010 at 09:29:40PM +1100, Dave Chinner wrote:
> > Yes, actually it is - see the XFS_IRECLAIMABLE case in
> > xfs_iget_cache_hit(). I guess we haven't seen the original lock
> > inversion false positives that this was supposed to fix because the
> > reclaim warnings trip first...
> > 
> > I think that means we also need to reinitialise the lock when we recycle
> > the inode out of the XFS_IRECLAIMABLE state.
> 
> I came up with the patch below when we had a previous report of the
> warning, but I couldn't convince myself that it really helps:
> 
> Index: linux-2.6/fs/xfs/xfs_iget.c
> ===================================================================
> --- linux-2.6.orig/fs/xfs/xfs_iget.c  2010-09-20 12:10:28.227444173 -0300
> +++ linux-2.6/fs/xfs/xfs_iget.c       2010-09-20 12:11:25.631444190 -0300
> @@ -207,6 +207,10 @@ xfs_iget_cache_hit(
>  
>                       ip->i_flags &= ~XFS_INEW;
>                       ip->i_flags |= XFS_IRECLAIMABLE;
> +
> +                     ASSERT(!rwsem_is_locked(&ip->i_iolock.mr_lock));
> +                     mrlock_init(&ip->i_iolock, MRLOCK_BARRIER, "xfsio", 
> ip->i_ino);
> +
>                       __xfs_inode_set_reclaim_tag(pag, ip);
>                       trace_xfs_iget_reclaim_fail(ip);
>                       goto out_error;


That adds a 3rd class which should work, but doesn't validate that the
first -- xfs_inode_alloc() and this one are in fact similar.


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