From: Michal Kubecek <mkubecek@suse.cz>

Date: Fri, 21 Jan 2022 01:15:39 +0100

Subject: net: allow retransmitting a TCP packet if original is still in queue

Patch-mainline: Never, temporary workaround

References: bsc#1188605 bsc#1187428 bsc#1206619

This effectively reverts mainline commit 1f3279ae0c13 ("tcp: avoid

retransmits of TCP packets hanging in host queues") so that the retransmit

can unblock the previous transmit of a TCP packet if it was left in the

qdisc queue of pfifo_fast due to a race condition in lockless qdisc code.

Rather than a full revert, just let skb_still_in_host_queue() always return

false so that everything else works exactly as before.

This is only a temporary workaround until the bsc#1188605 race condition is

identified and fixed.

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>

---

 net/ipv4/tcp_output.c | 4 +++-

 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/ipv4/tcp_output.c

+++ b/net/ipv4/tcp_output.c

@@ -2785,7 +2785,9 @@ static bool skb_still_in_host_queue(struct sock *sk,

 		if (skb_fclone_busy(sk, skb)) {

 			NET_INC_STATS(sock_net(sk),

 				      LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);

-			return true;

+			/* unclog the qdisc queue if previous transmit is still

+			 * there because of a race condition

+			 */

 		}

 	}

 	return false;