[PATCH 4.4 75/91] gfs2: Add missing rcu locking for glock lookup

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andrew Price <anprice@xxxxxxxxxx>

commit f38e5fb95a1f8feda88531eedc98f69b24748712 upstream.

We must hold the rcu read lock across looking up glocks and trying to
bump their refcount to prevent the glocks from being freed in between.

Signed-off-by: Andrew Price <anprice@xxxxxxxxxx>
Signed-off-by: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
Signed-off-by: Bob Peterson <rpeterso@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/gfs2/glock.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -651,9 +651,11 @@ int gfs2_glock_get(struct gfs2_sbd *sdp,
 	struct kmem_cache *cachep;
 	int ret, tries = 0;
 
+	rcu_read_lock();
 	gl = rhashtable_lookup_fast(&gl_hash_table, &name, ht_parms);
 	if (gl && !lockref_get_not_dead(&gl->gl_lockref))
 		gl = NULL;
+	rcu_read_unlock();
 
 	*glp = gl;
 	if (gl)
@@ -721,15 +723,18 @@ again:
 
 	if (ret == -EEXIST) {
 		ret = 0;
+		rcu_read_lock();
 		tmp = rhashtable_lookup_fast(&gl_hash_table, &name, ht_parms);
 		if (tmp == NULL || !lockref_get_not_dead(&tmp->gl_lockref)) {
 			if (++tries < 100) {
+				rcu_read_unlock();
 				cond_resched();
 				goto again;
 			}
 			tmp = NULL;
 			ret = -ENOMEM;
 		}
+		rcu_read_unlock();
 	} else {
 		WARN_ON_ONCE(ret);
 	}