Btrfs: properly wait log writers during log sync

A recently fsync optimization make btrfs_sync_log skip calling
wait_for_writer in the single log writer case. This is incorrect
since the writer count can also be increased by btrfs_pin_log.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 4aff766..f51bf13 100644 (file)
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -1995,12 +1995,13 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
        if (atomic_read(&root->log_commit[(index1 + 1) % 2]))
                wait_log_commit(trans, root, root->log_transid - 1);
 
-       while (root->log_multiple_pids) {
+       while (1) {
                unsigned long batch = root->log_batch;
-               mutex_unlock(&root->log_mutex);
-               schedule_timeout_uninterruptible(1);
-               mutex_lock(&root->log_mutex);
-
+               if (root->log_multiple_pids) {
+                       mutex_unlock(&root->log_mutex);
+                       schedule_timeout_uninterruptible(1);
+                       mutex_lock(&root->log_mutex);
+               }
                wait_for_writer(trans, root);
                if (batch == root->log_batch)
                        break;