On Thu, Nov 25, 2010 at 07:25:25AM +0100, Peter Zijlstra wrote: > On Thu, 2010-11-25 at 14:48 +1100, Nick Piggin wrote: > > On Wed, Nov 24, 2010 at 03:03:41PM -0500, Christoph Hellwig wrote: > > > On Wed, Nov 24, 2010 at 08:12:58AM +1100, Dave Chinner wrote: > > > > It is supposed to be handled by the re-initialisation of the > > > > ip->i_iolock in ->evict_inode (xfs_fs_evict_inode). An inode found > > > > in the reclaim state must have passed through this reinitialisation, > > > > so from a lockdep perspective the iolock in the vfs path is a > > > > different context to the iolock in the reclaim path. That fixed all > > > > the non-reclaim state related lockdep false positives, so Perhaps > > > > there is an issue with the lockdep reclaim state checking that does > > > > not interact well with re-initialised lock contexts? > > > > > > I've been looking through this again, and I think it's indeed not > > > enough. We don't just need to re-initialize it, but also set a > > > different lockclass for it. > > > > Doesn't init_rwsem give it a new class? > > Per call-site, yes it should. > > > Guys, can you take a quick look at the code Dave is referring to > > (xfs_fs_evict_inode), and check that it actually does what he > > intends? > > Right, so this is trying to set a different class from the regular init > site, which (/me applies grep) lives in xfs_inode_alloc(), right? > > Ought to work.. assuming the inode will be fully destroyed and new > inodes are always obtained through xfs_inode_alloc() and not reused. > > > We're getting what seems to be false positives in reclaim inversion > > of lockings. Backtraces here > > http://oss.sgi.com/pipermail/xfs/2010-November/048092.html > > Right, so there its holding the inode in the read path while taking a > page-fault which does an allocation. > > vs > > acquiring the inode in the xfs_reclaim_node_shrink() path. > > > Presumably the whole xfs_fs_evict_inode() stuff will happen _after_ its > possible to end up in that read path? > > > Something like the below would give the lock-class an explicit name, > because both sites now use the exact same init thing they're called: > > (&(&ip->i_iolock)->mr_lock) > (&(&ip->i_iolock)->mr_lock#2) > > Which is hard to tell apart, but I suspect #2 is the dead one, since > they get numbered in order of appearance and its hard to have a dead > inode before having a life one ;-) > > In that case though, it would suggest the inode got re-used instead of > destroyed and re-created using xfs_alloc_inode(), is that at all > possible? 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. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
