1 files changed, 30 insertions, 15 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index d0a2b7e4938..69139a356f7 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -53,7 +53,7 @@ static noinline void switch_commit_root(struct btrfs_root *root)
 /*
  * either allocate a new transaction or hop into the existing one
  */
-static noinline int join_transaction(struct btrfs_root *root, int nofail)
+static noinline int join_transaction(struct btrfs_root *root, int type)
 {
 	struct btrfs_transaction *cur_trans;
 	struct btrfs_fs_info *fs_info = root->fs_info;
@@ -67,7 +67,13 @@ loop:
 	}
 
 	if (fs_info->trans_no_join) {
-		if (!nofail) {
+		/* 
+		 * If we are JOIN_NOLOCK we're already committing a current
+		 * transaction, we just need a handle to deal with something
+		 * when committing the transaction, such as inode cache and
+		 * space cache. It is a special case.
+		 */
+		if (type != TRANS_JOIN_NOLOCK) {
 			spin_unlock(&fs_info->trans_lock);
 			return -EBUSY;
 		}
@@ -87,6 +93,13 @@ loop:
 	}
 	spin_unlock(&fs_info->trans_lock);
 
+	/*
+	 * If we are ATTACH, we just want to catch the current transaction,
+	 * and commit it. If there is no transaction, just return ENOENT.
+	 */
+	if (type == TRANS_ATTACH)
+		return -ENOENT;
+
 	cur_trans = kmem_cache_alloc(btrfs_transaction_cachep, GFP_NOFS);
 	if (!cur_trans)
 		return -ENOMEM;
@@ -340,27 +353,28 @@ again:
 	 * because we're already holding a ref.  We need this because we could
 	 * have raced in and did an fsync() on a file which can kick a commit
 	 * and then we deadlock with somebody doing a freeze.
+	 *
+	 * If we are ATTACH, it means we just want to catch the current
+	 * transaction and commit it, so we needn't do sb_start_intwrite(). 
 	 */
-	if (type != TRANS_JOIN_NOLOCK &&
-	    !__sb_start_write(root->fs_info->sb, SB_FREEZE_FS, false)) {
-		if (type == TRANS_JOIN_FREEZE) {
-			kmem_cache_free(btrfs_trans_handle_cachep, h);
-			return ERR_PTR(-EPERM);
-		}
+	if (type < TRANS_JOIN_NOLOCK)
 		sb_start_intwrite(root->fs_info->sb);
-	}
 
 	if (may_wait_transaction(root, type))
 		wait_current_trans(root);
 
 	do {
-		ret = join_transaction(root, type == TRANS_JOIN_NOLOCK);
+		ret = join_transaction(root, type);
 		if (ret == -EBUSY)
 			wait_current_trans(root);
 	} while (ret == -EBUSY);
 
 	if (ret < 0) {
-		sb_end_intwrite(root->fs_info->sb);
+		/* We must get the transaction if we are JOIN_NOLOCK. */
+		BUG_ON(type == TRANS_JOIN_NOLOCK);
+
+		if (type < TRANS_JOIN_NOLOCK)
+			sb_end_intwrite(root->fs_info->sb);
 		kmem_cache_free(btrfs_trans_handle_cachep, h);
 		return ERR_PTR(ret);
 	}
@@ -432,9 +446,9 @@ struct btrfs_trans_handle *btrfs_start_ioctl_transaction(struct btrfs_root *root
 	return start_transaction(root, 0, TRANS_USERSPACE, 0);
 }
 
-struct btrfs_trans_handle *btrfs_join_transaction_freeze(struct btrfs_root *root)
+struct btrfs_trans_handle *btrfs_attach_transaction(struct btrfs_root *root)
 {
-	return start_transaction(root, 0, TRANS_JOIN_FREEZE, 0);
+	return start_transaction(root, 0, TRANS_ATTACH, 0);
 }
 
 /* wait for a transaction commit to be fully complete */
@@ -605,7 +619,7 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
 		}
 	}
 
-	if (lock)
+	if (trans->type < TRANS_JOIN_NOLOCK)
 		sb_end_intwrite(root->fs_info->sb);
 
 	WARN_ON(cur_trans != info->running_transaction);
@@ -1678,7 +1692,8 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 	put_transaction(cur_trans);
 	put_transaction(cur_trans);
 
-	sb_end_intwrite(root->fs_info->sb);
+	if (trans->type < TRANS_JOIN_NOLOCK)
+		sb_end_intwrite(root->fs_info->sb);
 
 	trace_btrfs_transaction_commit(root);