Btrfs: fix a deadlock in aborting transaction due to ENOSPC

When committing a transaction, we may bail out of running delayed refs
due to ENOSPC, and then abort the current transaction to flip into readonly.

But we'll hit a deadlock on ref head's lock since we forget to release
its lock and other cleanup stuff.
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

fs/btrfs/extent-tree.c

@@ -2297,6 +2297,9 @@ static noinline int run_clustered_refs(struct btrfs_trans_handle *trans,
 				kfree(extent_op);
 
 				if (ret) {
+					list_del_init(&locked_ref->cluster);
+					mutex_unlock(&locked_ref->mutex);
+
 					printk(KERN_DEBUG "btrfs: run_delayed_extent_op returned %d\n", ret);
 					spin_lock(&delayed_refs->lock);
 					return ret;
@@ -2339,6 +2342,10 @@ static noinline int run_clustered_refs(struct btrfs_trans_handle *trans,
 		count++;
 
 		if (ret) {
+			if (locked_ref) {
+				list_del_init(&locked_ref->cluster);
+				mutex_unlock(&locked_ref->mutex);
+			}
 			printk(KERN_DEBUG "btrfs: run_one_delayed_ref returned %d\n", ret);
 			spin_lock(&delayed_refs->lock);
 			return ret;