ocfs2: add missing annotation for dlm_empty_lockres()

Sparse reports a warning at dlm_empty_lockres()

  warning: context imbalance in dlm_purge_lockres() - unexpected unlock

The root cause is the missing annotation at dlm_purge_lockres()

Add the missing __must_hold(&dlm->spinlock)

Signed-off-by: Jules Irenge <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Reviewed-by: Andrew Morton <[email protected]>
Cc: Mark Fasheh <[email protected]>
Cc: Joel Becker <[email protected]>
Cc: Junxiao Bi <[email protected]>
Cc: Joseph Qi <[email protected]>
Cc: Changwei Ge <[email protected]>
Cc: Gang He <[email protected]>
Cc: Jun Piao <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

Author: irenge

fs/ocfs2/dlm/dlmmaster.c

@@ -2760,6 +2760,7 @@ static int dlm_migrate_lockres(struct dlm_ctxt *dlm,
  * Returns: 1 if dlm->spinlock was dropped/retaken, 0 if never dropped
  */
 int dlm_empty_lockres(struct dlm_ctxt *dlm, struct dlm_lock_resource *res)
+	__must_hold(&dlm->spinlock)
 {
 	int ret;
 	int lock_dropped = 0;