XFS reclaim lock order bug

[Christoph Hellwig]

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;