GFS2: Fix race between lru_list and glock ref count

This patch fixes a narrow race window between the glock ref count
hitting zero and glocks being removed from the lru_list.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 10 insertions, 4 deletions

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 376816fcd040..351a3e797789 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -167,14 +167,19 @@ void gfs2_glock_add_to_lru(struct gfs2_glock *gl)
         spin_unlock(&lru_lock);
 }
 
-static void gfs2_glock_remove_from_lru(struct gfs2_glock *gl)
+static void __gfs2_glock_remove_from_lru(struct gfs2_glock *gl)
 {
-        spin_lock(&lru_lock);
         if (!list_empty(&gl->gl_lru)) {
                 list_del_init(&gl->gl_lru);
                 atomic_dec(&lru_count);
                 clear_bit(GLF_LRU, &gl->gl_flags);
         }
+}
+
+static void gfs2_glock_remove_from_lru(struct gfs2_glock *gl)
+{
+        spin_lock(&lru_lock);
+        __gfs2_glock_remove_from_lru(gl);
         spin_unlock(&lru_lock);
 }
 
@@ -217,11 +222,12 @@ void gfs2_glock_put(struct gfs2_glock *gl)
         struct gfs2_sbd *sdp = gl->gl_sbd;
         struct address_space *mapping = gfs2_glock2aspace(gl);
 
-        if (atomic_dec_and_test(&gl->gl_ref)) {
+        if (atomic_dec_and_lock(&gl->gl_ref, &lru_lock)) {
+                __gfs2_glock_remove_from_lru(gl);
+                spin_unlock(&lru_lock);
                 spin_lock_bucket(gl->gl_hash);
                 hlist_bl_del_rcu(&gl->gl_list);
                 spin_unlock_bucket(gl->gl_hash);
-                gfs2_glock_remove_from_lru(gl);
                 GLOCK_BUG_ON(gl, !list_empty(&gl->gl_holders));
                 GLOCK_BUG_ON(gl, mapping && mapping->nrpages);
                 trace_gfs2_glock_put(gl);