Patch "tcp/dccp: block bh before arming time_wait timer" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

tcp/dccp: block bh before arming time_wait timer

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
tcp-dccp-block-bh-before-arming-time_wait-timer.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Dumazet <[email protected]>
Date: Fri, 1 Dec 2017 10:06:56 -0800
Subject: tcp/dccp: block bh before arming time_wait timer

From: Eric Dumazet <[email protected]>

[ Upstream commit cfac7f836a715b91f08c851df915d401a4d52783 ]

Maciej Żenczykowski reported some panics in tcp_twsk_destructor() that might be caused by the following bug.

timewait timer is pinned to the cpu, because we want to transition timwewait refcount from 0 to 4 in one go, once everything has been initialized.

At the time commit ed2e92394589 ("tcp/dccp: fix timewait races in timer handling") was merged, TCP was always running from BH habdler.

After commit 5413d1babe8f ("net: do not block BH while processing socket backlog") we definitely can run tcp_time_wait() from process context.

We need to block BH in the critical section so that the pinned timer has still its purpose.

This bug is more likely to happen under stress and when very small RTO are used in datacenter flows.

---
 net/dccp/minisocks.c     |    6 ++++++
 net/ipv4/tcp_minisocks.c |    6 ++++++
 2 files changed, 12 insertions(+)

@@ -57,10 +57,16 @@ void dccp_time_wait(struct sock *sk, int
 		if (state == DCCP_TIME_WAIT)
 			timeo = DCCP_TIMEWAIT_LEN;
 
+		/* tw_timer is pinned, so we need to make sure BH are disabled
+		 * in following section, otherwise timer handler could run before
+		 * we complete the initialization.
+		 */
+		local_bh_disable();
 		inet_twsk_schedule(tw, timeo);
 		/* Linkage updates. */
 		__inet_twsk_hashdance(tw, sk, &dccp_hashinfo);
 		inet_twsk_put(tw);
+		local_bh_enable();
 	} else {
 		/* Sorry, if we're out of memory, just CLOSE this
 		 * socket up.  We've got bigger problems than

@@ -312,10 +312,16 @@ void tcp_time_wait(struct sock *sk, int
 		if (state == TCP_TIME_WAIT)
 			timeo = TCP_TIMEWAIT_LEN;
 
+		/* tw_timer is pinned, so we need to make sure BH are disabled
+		 * in following section, otherwise timer handler could run before
+		 * we complete the initialization.
+		 */
+		local_bh_disable();
 		inet_twsk_schedule(tw, timeo);
 		/* Linkage updates. */
 		__inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
 		inet_twsk_put(tw);
+		local_bh_enable();
 	} else {
 		/* Sorry, if we're out of memory, just CLOSE this
 		 * socket up.  We've got bigger problems than

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/tcp-add-tcp_v4_fill_cb-tcp_v4_restore_cb.patch queue-4.14/net-thunderx-fix-tcp-udp-checksum-offload-for-ipv6-pkts.patch queue-4.14/tcp-remove-buggy-call-to-tcp_v6_restore_cb.patch queue-4.14/net-packet-fix-a-race-in-packet_bind-and-packet_notifier.patch queue-4.14/tcp-use-ipcb-instead-of-tcp_skb_cb-in-inet_exact_dif_match.patch queue-4.14/net-thunderx-fix-tcp-udp-checksum-offload-for-ipv4-pkts.patch queue-4.14/packet-fix-crash-in-fanout_demux_rollover.patch queue-4.14/net-remove-hlist_nulls_add_tail_rcu.patch queue-4.14/tcp-when-scheduling-tlp-time-of-rto-should-account-for-current-ack.patch queue-4.14/tcp-dccp-block-bh-before-arming-time_wait-timer.patch queue-4.14/tcp-use-current-time-in-tcp_rcv_space_adjust.patch