1 files changed, 9 insertions, 5 deletions

diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index 272f911203ff..a44eff074805 100644
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -78,13 +78,15 @@ void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
                 write_lock(&eb->lock);
                 WARN_ON(atomic_read(&eb->spinning_writers));
                 atomic_inc(&eb->spinning_writers);
-                if (atomic_dec_and_test(&eb->blocking_writers))
+                if (atomic_dec_and_test(&eb->blocking_writers) &&
+                    waitqueue_active(&eb->write_lock_wq))
                         wake_up(&eb->write_lock_wq);
         } else if (rw == BTRFS_READ_LOCK_BLOCKING) {
                 BUG_ON(atomic_read(&eb->blocking_readers) == 0);
                 read_lock(&eb->lock);
                 atomic_inc(&eb->spinning_readers);
-                if (atomic_dec_and_test(&eb->blocking_readers))
+                if (atomic_dec_and_test(&eb->blocking_readers) &&
+                    waitqueue_active(&eb->read_lock_wq))
                         wake_up(&eb->read_lock_wq);
         }
         return;
@@ -199,7 +201,8 @@ void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
         }
         btrfs_assert_tree_read_locked(eb);
         WARN_ON(atomic_read(&eb->blocking_readers) == 0);
-        if (atomic_dec_and_test(&eb->blocking_readers))
+        if (atomic_dec_and_test(&eb->blocking_readers) &&
+            waitqueue_active(&eb->read_lock_wq))
                 wake_up(&eb->read_lock_wq);
         atomic_dec(&eb->read_locks);
 }
@@ -247,8 +250,9 @@ void btrfs_tree_unlock(struct extent_buffer *eb)
         if (blockers) {
                 WARN_ON(atomic_read(&eb->spinning_writers));
                 atomic_dec(&eb->blocking_writers);
-                smp_wmb();
-                wake_up(&eb->write_lock_wq);
+                smp_mb();
+                if (waitqueue_active(&eb->write_lock_wq))
+                        wake_up(&eb->write_lock_wq);
         } else {
                 WARN_ON(atomic_read(&eb->spinning_writers) != 1);
                 atomic_dec(&eb->spinning_writers);