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>

1 files changed, 6 insertions, 5 deletions

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 4aff766d171a..f51bf13125c0 100644
--- 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;