GFS2: Fix potential race in glock code

We need to be careful of the ordering between clearing the
GLF_LOCK bit and scheduling the workqueue.

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

1 files changed, 8 insertions, 2 deletions

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 8b674b1f3a5..a3f90ad2af8 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -672,12 +672,17 @@ out:
         return;
 
 out_sched:
+        clear_bit(GLF_LOCK, &gl->gl_flags);
+        smp_mb__after_clear_bit();
         gfs2_glock_hold(gl);
         if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
                 gfs2_glock_put_nolock(gl);
+        return;
+
 out_unlock:
         clear_bit(GLF_LOCK, &gl->gl_flags);
-        goto out;
+        smp_mb__after_clear_bit();
+        return;
 }
 
 static void delete_work_func(struct work_struct *work)
@@ -1375,10 +1380,11 @@ static int gfs2_shrink_glock_memory(int nr, gfp_t gfp_mask)
                                 handle_callback(gl, LM_ST_UNLOCKED, 0);
                                 nr--;
                         }
+                        clear_bit(GLF_LOCK, &gl->gl_flags);
+                        smp_mb__after_clear_bit();
                         if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
                                 gfs2_glock_put_nolock(gl);
                         spin_unlock(&gl->gl_spin);
-                        clear_bit(GLF_LOCK, &gl->gl_flags);
                         spin_lock(&lru_lock);
                         continue;
                 }