[34-longterm 137/209] tcp: Don't change unlocked socket state in tcp_v4_err().

[Paul Gortmaker]

From: David S. Miller <davem@xxxxxxxxxxxxx>

  =====================================================================
  | This is a commit scheduled for the next v2.6.34 longterm release. |
  | If you see a problem with using this for longterm, please comment.|
  =====================================================================

commit 8f49c2703b33519aaaccc63f571b465b9d2b3a2d upstream

Alexey Kuznetsov noticed a regression introduced by
commit f1ecd5d9e7366609d640ff4040304ea197fbc618
("Revert Backoff [v3]: Revert RTO on ICMP destination unreachable")

The RTO and timer modification code added to tcp_v4_err()
doesn't check sock_owned_by_user(), which if true means we
don't have exclusive access to the socket and therefore cannot
modify it's critical state.

Just skip this new code block if sock_owned_by_user() is true
and eliminate the now superfluous sock_owned_by_user() code
block contained within.

Reported-by: Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
CC: Damian Lukowski <damian@xxxxxxxxxxxxxxxxxx>
Acked-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
 net/ipv4/tcp_ipv4.c |    8 +++-----
 1 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 3c23e70..ea51c2f 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -411,6 +411,9 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
 		    !icsk->icsk_backoff)
 			break;
 
+		if (sock_owned_by_user(sk))
+			break;
+
 		icsk->icsk_backoff--;
 		inet_csk(sk)->icsk_rto = __tcp_set_rto(tp) <<
 					 icsk->icsk_backoff;
@@ -425,11 +428,6 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
 		if (remaining) {
 			inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 						  remaining, TCP_RTO_MAX);
-		} else if (sock_owned_by_user(sk)) {
-			/* RTO revert clocked out retransmission,
-			 * but socket is locked. Will defer. */
-			inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
-						  HZ/20, TCP_RTO_MAX);
 		} else {
 			/* RTO revert clocked out retransmission.
 			 * Will retransmit now */
-- 
1.7.4.4

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