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>

2 files changed, 18 insertions, 9 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 5022e62e63a8..7b1f614f51f6 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3065,16 +3065,22 @@ static noinline long btrfs_ioctl_start_sync(struct btrfs_root *root,
         u64 transid;
         int ret;
 
-        trans = btrfs_start_transaction(root, 0);
-        if (IS_ERR(trans))
-                return PTR_ERR(trans);
+        trans = btrfs_attach_transaction(root);
+        if (IS_ERR(trans)) {
+                if (PTR_ERR(trans) != -ENOENT)
+                        return PTR_ERR(trans);
+
+                /* No running transaction, don't bother */
+                transid = root->fs_info->last_trans_committed;
+                goto out;
+        }
         transid = trans->transid;
         ret = btrfs_commit_transaction_async(trans, root, 0);
         if (ret) {
                 btrfs_end_transaction(trans, root);
                 return ret;
         }
-
+out:
         if (argp)
                 if (copy_to_user(argp, &transid, sizeof(transid)))
                         return -EFAULT;
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);