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[PATCH 3.18 04/22] tcp: when rearming RTO, if RTO time is in past then fire RTO ASAP

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3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Neal Cardwell <ncardwell@google.com>


[ Upstream commit cdbeb633ca71a02b7b63bfeb94994bf4e1a0b894 ]

In some situations tcp_send_loss_probe() can realize that it's unable
to send a loss probe (TLP), and falls back to calling tcp_rearm_rto()
to schedule an RTO timer. In such cases, sometimes tcp_rearm_rto()
realizes that the RTO was eligible to fire immediately or at some
point in the past (delta_us <= 0). Previously in such cases
tcp_rearm_rto() was scheduling such "overdue" RTOs to happen at now +
icsk_rto, which caused needless delays of hundreds of milliseconds
(and non-linear behavior that made reproducible testing
difficult). This commit changes the logic to schedule "overdue" RTOs
ASAP, rather than at now + icsk_rto.

Fixes: 6ba8a3b19e76 ("tcp: Tail loss probe (TLP)")
Suggested-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv4/tcp_input.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2985,8 +2985,7 @@ void tcp_rearm_rto(struct sock *sk)
 			/* delta may not be positive if the socket is locked
 			 * when the retrans timer fires and is rescheduled.
 			 */
-			if (delta > 0)
-				rto = delta;
+			rto = max(delta, 1);
 		}
 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
 					  TCP_RTO_MAX);

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[PATCH 3.18 00/22] 3.18.68-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:20 +0200
  [PATCH 3.18 19/22] Bluetooth: bnep: fix possible might sleep error in bnep_session Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:20 +0200
  [PATCH 3.18 05/22] irda: do not leak initialized list.dev to userspace Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:20 +0200
  [PATCH 3.18 20/22] iio: imu: adis16480: Fix acceleration scale factor for adis16480 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:20 +0200
  [PATCH 3.18 01/22] dccp: purge write queue in dccp_destroy_sock() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:20 +0200
  [PATCH 3.18 13/22] cifs: Fix df output for users with quota limits Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:20 +0200
  [PATCH 3.18 03/22] sctp: fully initialize the IPv6 address in sctp_v6_to_addr() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:20 +0200
  [PATCH 3.18 07/22] net_sched: fix order of queue length updates in qdisc_replace() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:20 +0200
  [PATCH 3.18 22/22] ACPI / APEI: Add missing synchronize_rcu() on NOTIFY_SCI removal Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:20 +0200
  [PATCH 3.18 17/22] Bluetooth: hidp: fix possible might sleep error in hidp_session_thread Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:20 +0200
  [PATCH 3.18 09/22] ALSA: core: Fix unexpected error at replacing user TLV Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:20 +0200
  [PATCH 3.18 06/22] net: sched: fix NULL pointer dereference when action calls some targets Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:20 +0200
  [PATCH 3.18 04/22] tcp: when rearming RTO, if RTO time is in past then fire RTO ASAP Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:20 +0200
  [PATCH 3.18 08/22] Input: trackpoint - add new trackpoint firmware ID Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:20 +0200
  [PATCH 3.18 12/22] tracing: Fix freeing of filter in create_filter() when set_str is false Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:30 +0200
  [PATCH 3.18 18/22] Bluetooth: cmtp: fix possible might sleep error in cmtp_session Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:30 +0200
  [PATCH 3.18 14/22] cifs: return ENAMETOOLONG for overlong names in cifs_open()/cifs_lookup() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:30 +0200
  [PATCH 3.18 02/22] dccp: defer ccid_hc_tx_delete() at dismantle time Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:30 +0200
  [PATCH 3.18 10/22] ALSA: hda - Add stereo mic quirk for Lenovo G50-70 (17aa:3978) Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:30 +0200
  [PATCH 3.18 16/22] perf/core: Fix group {cpu,task} validation Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:30 +0200
  [PATCH 3.18 21/22] staging: rtl8188eu: add RNX-N150NUB support Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-28 10:30 +0200
  Re: [PATCH 3.18 00/22] 3.18.68-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-08-28 21:40 +0200
  Re: [PATCH 3.18 00/22] 3.18.68-stable review Guenter Roeck <linux@roeck-us.net> - 2017-08-29 02:10 +0200

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