[PATCH 4.9 118/153] gfs2: Add missing rcu locking for glock lookup

[Greg Kroah-Hartman]

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

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

From: Andrew Price <anpr...@redhat.com>

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 <anpr...@redhat.com>
Signed-off-by: Andreas Gruenbacher <agrue...@redhat.com>
Signed-off-by: Bob Peterson <rpete...@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

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

--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -658,9 +658,11 @@ 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)
@@ -728,15 +730,18 @@ 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);
        }