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;