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Re: XFS reclaim lock order bug

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: XFS reclaim lock order bug
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Thu, 25 Nov 2010 06:25:30 -0500
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Nick Piggin <npiggin@xxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <20101125102940.GE12187@dastard>
References: <20101123121802.GA4785@amd> <20101123211258.GY22876@dastard> <20101124200341.GA2493@xxxxxxxxxxxxx> <20101125034824.GA3359@amd> <1290666325.2072.535.camel@laptop> <20101125102940.GE12187@dastard>
User-agent: Mutt/1.5.21 (2010-09-15)
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;

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