xfs: provide a inode iolock lockdep class

The XFS iolock needs to be re-initialised to a new lock class before
it enters reclaim to prevent lockdep false positives. Unfortunately,
this is not sufficient protection as inodes in the XFS_IRECLAIMABLE
state can be recycled and not re-initialised before being reused.

We need to re-initialise the lock state when transfering out of
XFS_IRECLAIMABLE state to XFS_INEW, but we need to keep the same
class as if the inode was just allocated. Hence we need a specific
lockdep class variable for the iolock so that both initialisations
use the same class.

While there, add a specific class for inodes in the reclaim state so
that it is easy to tell from lockdep reports what state the inode
was in that generated the report.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/linux-2.6/xfs_super.c

@@ -1118,6 +1118,8 @@ xfs_fs_evict_inode(
 	 */
 	ASSERT(!rwsem_is_locked(&ip->i_iolock.mr_lock));
 	mrlock_init(&ip->i_iolock, MRLOCK_BARRIER, "xfsio", ip->i_ino);
+	lockdep_set_class_and_name(&ip->i_iolock.mr_lock,
+			&xfs_iolock_reclaimable, "xfs_iolock_reclaimable");
 
 	xfs_inactive(ip);
 }

fs/xfs/xfs_iget.c

@@ -42,6 +42,17 @@
 #include "xfs_trace.h"
 
 
+/*
+ * Define xfs inode iolock lockdep classes. We need to ensure that all active
+ * inodes are considered the same for lockdep purposes, including inodes that
+ * are recycled through the XFS_IRECLAIMABLE state. This is the the only way to
+ * guarantee the locks are considered the same when there are multiple lock
+ * initialisation siteѕ. Also, define a reclaimable inode class so it is
+ * obvious in lockdep reports which class the report is against.
+ */
+static struct lock_class_key xfs_iolock_active;
+struct lock_class_key xfs_iolock_reclaimable;
+
 /*
  * Allocate and initialise an xfs_inode.
  */
@@ -71,6 +82,8 @@ xfs_inode_alloc(
 	ASSERT(completion_done(&ip->i_flush));
 
 	mrlock_init(&ip->i_iolock, MRLOCK_BARRIER, "xfsio", ip->i_ino);
+	lockdep_set_class_and_name(&ip->i_iolock.mr_lock,
+			&xfs_iolock_active, "xfs_iolock_active");
 
 	/* initialise the xfs inode */
 	ip->i_ino = ino;
@@ -218,6 +231,12 @@ xfs_iget_cache_hit(
 		ip->i_flags |= XFS_INEW;
 		__xfs_inode_clear_reclaim_tag(mp, pag, ip);
 		inode->i_state = I_NEW;
+
+		ASSERT(!rwsem_is_locked(&ip->i_iolock.mr_lock));
+		mrlock_init(&ip->i_iolock, MRLOCK_BARRIER, "xfsio", ip->i_ino);
+		lockdep_set_class_and_name(&ip->i_iolock.mr_lock,
+				&xfs_iolock_active, "xfs_iolock_active");
+
 		spin_unlock(&ip->i_flags_lock);
 		write_unlock(&pag->pag_ici_lock);
 	} else {

fs/xfs/xfs_inode.h

@@ -438,6 +438,8 @@ static inline void xfs_ifunlock(xfs_inode_t *ip)
 #define XFS_IOLOCK_DEP(flags)	(((flags) & XFS_IOLOCK_DEP_MASK) >> XFS_IOLOCK_SHIFT)
 #define XFS_ILOCK_DEP(flags)	(((flags) & XFS_ILOCK_DEP_MASK) >> XFS_ILOCK_SHIFT)
 
+extern struct lock_class_key xfs_iolock_reclaimable;
+
 /*
  * Flags for xfs_itruncate_start().
  */