On Mon, Nov 08, 2010 at 07:36:28PM -0800, Paul E. McKenney wrote: > On Mon, Nov 08, 2010 at 06:09:29PM -0500, Christoph Hellwig wrote: > > This patch generally looks good to me, but with so much RCU magic I'd prefer > > if Paul & Eric could look over it. > > Is there a git tree, tarball, or whatever? git://git.kernel.org/pub/scm/linux/kernel/git/dgc/xfsdev.git working contains the series that this patch is in. > For example, I don't see > how this patch handles the case of an inode being freed just as an RCU > reader gains a reference to it, XFS_IRECLAIM flag is set on inodes as they transition into the reclaim state long before they are freed. The XFS_IRECLAIM flag is left there once freed. Hence lookups in xfs_iget_cache_hit() will see this. If the inode has been reallocated, the inode number will not yet be set, or the inode state will have changed to XFS_INEW, both of which xfs_iget_cache_hit() will also reject. > but then reallocated as some other inode > (so that ->ino is nonzero) before the RCU reader gets a chance to actually > look at the inode. XFS_INEW is not cleared until well after a new ->i_ino is set, so the lookup should find trip over XFS_INEW in that case. I think that I may need to move the inode number check under the i_flags_lock after validating the flags - more to check that we've got the correct inode than to validate we have a freed inode. > But such a check might well be in the code that this > patch didn't change... Yeah, most of the XFS code is already in a form compatible with such RCU use because inodes have always had a quiescent "reclaimable" state between active and reclaim (XFS_INEW -> active -> XFS_IRECLAIMABLE -> XFS_IRECLAIM) where the inode can be reused before being freed. The result is that lookups have always had to handle races with inodes that have just transitioned into the XFS_IRECLAIM state and hence cannot be immediately reused... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
