af_unix: Define locking order for U_RECVQ_LOCK_EMBRYO in unix_collect_skb().

While GC is cleaning up cyclic references by SCM_RIGHTS,
unix_collect_skb() collects skb in the socket's recvq.

If the socket is TCP_LISTEN, we need to collect skb in the
embryo's queue.  Then, both the listener's recvq lock and
the embroy's one are held.

The locking is always done in the listener -> embryo order.

Let's define it as unix_recvq_lock_cmp_fn() instead of using
spin_lock_nested().

Note that the reverse order is defined for consistency.

Signed-off-by: Kuniyuki Iwashima <[email protected]>
Signed-off-by: Paolo Abeni <[email protected]>

1 files changed, 1 insertions, 7 deletions

diff --git a/net/unix/garbage.c b/net/unix/garbage.c
index dfe94a90ece4..eb8aa5171a68 100644
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -337,11 +337,6 @@ static bool unix_vertex_dead(struct unix_vertex *vertex)
 	return true;
 }
 
-enum unix_recv_queue_lock_class {
-	U_RECVQ_LOCK_NORMAL,
-	U_RECVQ_LOCK_EMBRYO,
-};
-
 static void unix_collect_queue(struct unix_sock *u, struct sk_buff_head *hitlist)
 {
 	skb_queue_splice_init(&u->sk.sk_receive_queue, hitlist);
@@ -375,8 +370,7 @@ static void unix_collect_skb(struct list_head *scc, struct sk_buff_head *hitlist
 			skb_queue_walk(queue, skb) {
 				struct sk_buff_head *embryo_queue = &skb->sk->sk_receive_queue;
 
-				/* listener -> embryo order, the inversion never happens. */
-				spin_lock_nested(&embryo_queue->lock, U_RECVQ_LOCK_EMBRYO);
+				spin_lock(&embryo_queue->lock);
 				unix_collect_queue(unix_sk(skb->sk), hitlist);
 				spin_unlock(&embryo_queue->lock);
 			}