[PATCH] Btrfs: incremental send, fix infinite loop when apply children dir moves

[robbieko <robbieko@synology.com>]

From: Robbie Ko <robbieko@synology.com>

In apply_children_dir_moves, we first create an empty list (stack),
then we get an entry from pending_dir_moves and add it to the stack,
but we didn't delete the entry from rb_tree.

So, in add_pending_dir_move, we create a new entry and then use the
parent_ino in the current rb_tree to find the corresponding entry,
and if so, add the new entry to the corresponding list.

However, the entry may have been added to the stack, causing new
entries to be added to the stack as well.

Finally, each time we take the first entry from the stack and start
processing, it ends up with an infinite loop.

Fix this problem by remove node from pending_dir_moves,
avoid add new pending_dir_move to error list.

Signed-off-by: Robbie Ko <robbieko@synology.com>
---
 fs/btrfs/send.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 094cc144..5be83b5 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -3340,7 +3340,8 @@ static void free_pending_move(struct send_ctx *sctx, struct pending_dir_move *m)
 	kfree(m);
 }
 
-static void tail_append_pending_moves(struct pending_dir_move *moves,
+static void tail_append_pending_moves(struct send_ctx *sctx,
+				      struct pending_dir_move *moves,
 				      struct list_head *stack)
 {
 	if (list_empty(&moves->list)) {
@@ -3351,6 +3352,10 @@ static void tail_append_pending_moves(struct pending_dir_move *moves,
 		list_add_tail(&moves->list, stack);
 		list_splice_tail(&list, stack);
 	}
+	if (!RB_EMPTY_NODE(&moves->node)) {
+		rb_erase(&moves->node, &sctx->pending_dir_moves);
+		RB_CLEAR_NODE(&moves->node);
+	}
 }
 
 static int apply_children_dir_moves(struct send_ctx *sctx)
@@ -3365,7 +3370,7 @@ static int apply_children_dir_moves(struct send_ctx *sctx)
 		return 0;
 
 	INIT_LIST_HEAD(&stack);
-	tail_append_pending_moves(pm, &stack);
+	tail_append_pending_moves(sctx, pm, &stack);
 
 	while (!list_empty(&stack)) {
 		pm = list_first_entry(&stack, struct pending_dir_move, list);
@@ -3376,7 +3381,7 @@ static int apply_children_dir_moves(struct send_ctx *sctx)
 			goto out;
 		pm = get_pending_dir_moves(sctx, parent_ino);
 		if (pm)
-			tail_append_pending_moves(pm, &stack);
+			tail_append_pending_moves(sctx, pm, &stack);
 	}
 	return 0;
 
-- 
1.9.1