ocfs2/dlm: Do not purge lockres that is being migrated dlm_purge_lockres()

This patch attempts to fix a fine race between purging and migration.
Signed-off-by: Sunil Mushran <sunil.mushran@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>

fs/ocfs2/dlm/dlmthread.c

@@ -162,12 +162,28 @@ static int dlm_purge_lockres(struct dlm_ctxt *dlm,
 
 	spin_lock(&res->spinlock);
 	if (!__dlm_lockres_unused(res)) {
-		spin_unlock(&res->spinlock);
 		mlog(0, "%s:%.*s: tried to purge but not unused\n",
 		     dlm->name, res->lockname.len, res->lockname.name);
-		return -ENOTEMPTY;
+		__dlm_print_one_lock_resource(res);
+		spin_unlock(&res->spinlock);
+		BUG();
 	}
+
+	if (res->state & DLM_LOCK_RES_MIGRATING) {
+		mlog(0, "%s:%.*s: Delay dropref as this lockres is "
+		     "being remastered\n", dlm->name, res->lockname.len,
+		     res->lockname.name);
+		/* Re-add the lockres to the end of the purge list */
+		if (!list_empty(&res->purge)) {
+			list_del_init(&res->purge);
+			list_add_tail(&res->purge, &dlm->purge_list);
+		}
+		spin_unlock(&res->spinlock);
+		return 0;
+	}
+
 	master = (res->owner == dlm->node_num);
+
 	if (!master)
 		res->state |= DLM_LOCK_RES_DROPPING_REF;
 	spin_unlock(&res->spinlock);