GFS2: ignore unlock failures after withdraw

After gfs2 has withdrawn the filesystem, it may still have many locks not
in the unlocked state.  If it is using lock_dlm, it will failed trying
the unlocks since it has already unmounted the lock manager. Instead, it
should set the SDF_SKIP_DLM_UNLOCK flag on withdraw, to signal that
it can skip the lock_manager on unlocks, and failback to lock_nolock
style unlocking.

Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>

fs/gfs2/glock.c

@@ -475,7 +475,14 @@ __acquires(&gl->gl_lockref.lock)
 	if (sdp->sd_lockstruct.ls_ops->lm_lock)	{
 		/* lock_dlm */
 		ret = sdp->sd_lockstruct.ls_ops->lm_lock(gl, target, lck_flags);
-		if (ret) {
+		if (ret == -EINVAL && gl->gl_target == LM_ST_UNLOCKED &&
+		    target == LM_ST_UNLOCKED &&
+		    test_bit(SDF_SKIP_DLM_UNLOCK, &sdp->sd_flags)) {
+			finish_xmote(gl, target);
+			if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
+				gfs2_glock_put(gl);
+		}
+		else if (ret) {
 			pr_err("lm_lock ret %d\n", ret);
 			GLOCK_BUG_ON(gl, 1);
 		}