Merge branch 'fix/waitqueue-barriers' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux into for-linus-4.4

1 files changed, 12 insertions, 2 deletions

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index c3f9a9c71f28..1fffe8845c09 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -229,7 +229,9 @@ int btrfs_pin_log_trans(struct btrfs_root *root)
 void btrfs_end_log_trans(struct btrfs_root *root)
 {
         if (atomic_dec_and_test(&root->log_writers)) {
-                smp_mb();
+                /*
+                 * Implicit memory barrier after atomic_dec_and_test
+                 */
                 if (waitqueue_active(&root->log_writer_wait))
                         wake_up(&root->log_writer_wait);
         }
@@ -2820,7 +2822,9 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
 
         mutex_lock(&log_root_tree->log_mutex);
         if (atomic_dec_and_test(&log_root_tree->log_writers)) {
-                smp_mb();
+                /*
+                 * Implicit memory barrier after atomic_dec_and_test
+                 */
                 if (waitqueue_active(&log_root_tree->log_writer_wait))
                         wake_up(&log_root_tree->log_writer_wait);
         }
@@ -2950,6 +2954,9 @@ out_wake_log_root:
         atomic_set(&log_root_tree->log_commit[index2], 0);
         mutex_unlock(&log_root_tree->log_mutex);
 
+        /*
+         * The barrier before waitqueue_active is implied by mutex_unlock
+         */
         if (waitqueue_active(&log_root_tree->log_commit_wait[index2]))
                 wake_up(&log_root_tree->log_commit_wait[index2]);
 out:
@@ -2961,6 +2968,9 @@ out:
         atomic_set(&root->log_commit[index1], 0);
         mutex_unlock(&root->log_mutex);
 
+        /*
+         * The barrier before waitqueue_active is implied by mutex_unlock
+         */
         if (waitqueue_active(&root->log_commit_wait[index1]))
                 wake_up(&root->log_commit_wait[index1]);
         return ret;