gfs2: fix glock shrinker ref issues

Before this patch, function gfs2_scan_glock_lru would only try to free
glocks that had a reference count of 0. But if the reference count ever
got to 0, the glock should have already been freed.

Shrinker function gfs2_dispose_glock_lru checks whether glocks on the
LRU are demote_ok, and if so, tries to demote them. But that's only
possible if the reference count is at least 1.

This patch changes gfs2_scan_glock_lru so it will try to demote and/or
dispose of glocks that have a reference count of 1 and which are either
demotable, or are already unlocked.
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/glock.c

@@ -2010,7 +2010,9 @@ static long gfs2_scan_glock_lru(int nr)
 		if (!test_bit(GLF_LOCK, &gl->gl_flags)) {
 			if (!spin_trylock(&gl->gl_lockref.lock))
 				continue;
-			if (!gl->gl_lockref.count) {
+			if (gl->gl_lockref.count <= 1 &&
+			    (gl->gl_state == LM_ST_UNLOCKED ||
+			     demote_ok(gl))) {
 				list_move(&gl->gl_lru, &dispose);
 				atomic_dec(&lru_count);
 				freed++;