[PATCH] tcp: fix TCP socks unreleased in BBR mode

[kerneljasonxing]

From: Jason Xing <kerneljasonxing@xxxxxxxxx>

TCP socks cannot be released because of the sock_hold() increasing the
sk_refcnt in the manner of tcp_internal_pacing() when RTO happens.
Therefore, this situation could increase the slab memory and then trigger
the OOM if the machine has beening running for a long time. This issue,
however, can happen on some machine only running a few days.

We add one exception case to avoid unneeded use of sock_hold if the
pacing_timer is enqueued.

Reproduce procedure:
0) cat /proc/slabinfo | grep TCP
1) switch net.ipv4.tcp_congestion_control to bbr
2) using wrk tool something like that to send packages
3) using tc to increase the delay in the dev to simulate the busy case.
4) cat /proc/slabinfo | grep TCP
5) kill the wrk command and observe the number of objects and slabs in TCP.
6) at last, you could notice that the number would not decrease.

Signed-off-by: Jason Xing <kerneljasonxing@xxxxxxxxx>
Signed-off-by: liweishi <liweishi@xxxxxxxxxxxx>
Signed-off-by: Shujin Li <lishujin@xxxxxxxxxxxx>
---
 net/ipv4/tcp_output.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index cc4ba42..5cf63d9 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -969,7 +969,8 @@ static void tcp_internal_pacing(struct sock *sk, const struct sk_buff *skb)
 	u64 len_ns;
 	u32 rate;
 
-	if (!tcp_needs_internal_pacing(sk))
+	if (!tcp_needs_internal_pacing(sk) ||
+	    hrtimer_is_queued(&tcp_sk(sk)->pacing_timer))
 		return;
 	rate = sk->sk_pacing_rate;
 	if (!rate || rate == ~0U)
-- 
1.8.3.1