Btrfs: don't start a new transaction when starting sync

If there is no running transaction in the fs, we needn't start a new one when
we want to start sync.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

1 files changed, 8 insertions, 5 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index bcc6b65be3b0..8db401fa2f8f 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -1307,9 +1307,10 @@ static void do_async_commit(struct work_struct *work)
          * We've got freeze protection passed with the transaction.
          * Tell lockdep about it.
          */
-        rwsem_acquire_read(
-                &ac->root->fs_info->sb->s_writers.lock_map[SB_FREEZE_FS-1],
-                0, 1, _THIS_IP_);
+        if (ac->newtrans->type < TRANS_JOIN_NOLOCK)
+                rwsem_acquire_read(
+                     &ac->root->fs_info->sb->s_writers.lock_map[SB_FREEZE_FS-1],
+                     0, 1, _THIS_IP_);
 
         current->journal_info = ac->newtrans;
 
@@ -1347,8 +1348,10 @@ int btrfs_commit_transaction_async(struct btrfs_trans_handle *trans,
          * Tell lockdep we've released the freeze rwsem, since the
          * async commit thread will be the one to unlock it.
          */
-        rwsem_release(&root->fs_info->sb->s_writers.lock_map[SB_FREEZE_FS-1],
-                      1, _THIS_IP_);
+        if (trans->type < TRANS_JOIN_NOLOCK)
+                rwsem_release(
+                        &root->fs_info->sb->s_writers.lock_map[SB_FREEZE_FS-1],
+                        1, _THIS_IP_);
 
         schedule_delayed_work(&ac->work, 0);