btrfs: remove extra barrier before waitqueue_active

Removing barriers is scary, but a call to atomic_dec_and_test implies
a barrier, so we don't need to issue another one.

Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index d0deb46..6327559 100644 (file)
--- 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);
        }