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Yuchung Cheng fd2123a3d7 tcp: avoid resetting ACK timer upon receiving packet with ECN CWR flag
Previously commit 9aee400061 ("tcp: ack immediately when a cwr
packet arrives") calls tcp_enter_quickack_mode to force sending
two immediate ACKs upon receiving a packet w/ CWR flag. The side
effect is it'll also reset the delayed ACK timer and interactive
session tracking. This patch removes that side effect by using the
new ACK_NOW flag to force an immmediate ACK.

Packetdrill to demonstrate:

    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
   +0 setsockopt(3, SOL_TCP, TCP_CONGESTION, "dctcp", 5) = 0
   +0 bind(3, ..., ...) = 0
   +0 listen(3, 1) = 0

   +0 < [ect0] SEW 0:0(0) win 32792 <mss 1000,sackOK,nop,nop,nop,wscale 7>
   +0 > SE. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK,nop,wscale 8>
  +.1 < [ect0] . 1:1(0) ack 1 win 257
   +0 accept(3, ..., ...) = 4

   +0 < [ect0] . 1:1001(1000) ack 1 win 257
   +0 > [ect01] . 1:1(0) ack 1001

   +0 write(4, ..., 1) = 1
   +0 > [ect01] P. 1:2(1) ack 1001

   +0 < [ect0] . 1001:2001(1000) ack 2 win 257
   +0 write(4, ..., 1) = 1
   +0 > [ect01] P. 2:3(1) ack 2001

   +0 < [ect0] . 2001:3001(1000) ack 3 win 257
   +0 < [ect0] . 3001:4001(1000) ack 3 win 257
   // Ack delayed ...

   +.01 < [ce] P. 4001:4501(500) ack 3 win 257
   +0 > [ect01] . 3:3(0) ack 4001
   +0 > [ect01] E. 3:3(0) ack 4501

+.001 read(4, ..., 4500) = 4500
   +0 write(4, ..., 1) = 1
   +0 > [ect01] PE. 3:4(1) ack 4501 win 100

 +.01 < [ect0] W. 4501:5501(1000) ack 4 win 257
   // No delayed ACK on CWR flag
   +0 > [ect01] . 4:4(0) ack 5501

 +.31 < [ect0] . 5501:6501(1000) ack 4 win 257
   +0 > [ect01] . 4:4(0) ack 6501

Fixes: 9aee400061 ("tcp: ack immediately when a cwr packet arrives")
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2018-08-11 11:31:35 -07:00
arch Merge ra.kernel.org:/pub/scm/linux/kernel/git/davem/net 2018-08-09 11:52:36 -07:00
block Partially revert "block: fail op_is_write() requests to read-only partitions" 2018-08-04 18:19:55 -07:00
certs certs/blacklist: fix const confusion 2018-06-26 09:43:03 -07:00
crypto net: simplify sock_poll_wait 2018-07-30 09:10:25 -07:00
Documentation Merge branch 'for-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth-next 2018-08-10 14:24:57 -07:00
drivers wimax: usb-tx: mark expected switch fall-through 2018-08-11 11:29:36 -07:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs Merge ra.kernel.org:/pub/scm/linux/kernel/git/davem/net 2018-08-05 13:04:31 -07:00
include tcp: mandate a one-time immediate ACK 2018-08-11 11:31:35 -07:00
init Kbuild fixes for v4.18 2018-06-30 13:05:30 -07:00
ipc Merge ra.kernel.org:/pub/scm/linux/kernel/git/davem/net 2018-08-05 13:04:31 -07:00
kernel Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2018-08-07 11:02:05 -07:00
lib Merge ra.kernel.org:/pub/scm/linux/kernel/git/davem/net 2018-08-02 10:55:32 -07:00
LICENSES LICENSES: Add Linux-OpenIB license text 2018-04-27 16:41:53 -06:00
mm ipc/shm.c add ->pagesize function to shm_vm_ops 2018-08-02 16:03:40 -07:00
net tcp: avoid resetting ACK timer upon receiving packet with ECN CWR flag 2018-08-11 11:31:35 -07:00
samples samples/bpf: extend test_cgrp2_attach2 test to use cgroup storage 2018-08-03 00:47:33 +02:00
scripts Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-07-18 19:32:54 -07:00
security net: sched: introduce chain object to uapi 2018-07-23 20:44:12 -07:00
sound ALSA: hda/realtek - Yet another Clevo P950 quirk entry 2018-07-18 12:17:46 +02:00
tools selftests: mlxsw: Add TC flower test for Spectrum-2 2018-08-09 10:36:10 -07:00
usr kbuild: rename built-in.o to built-in.a 2018-03-26 02:01:19 +09:00
virt Miscellaneous bugfixes, plus a small patchlet related to Spectre v2. 2018-07-18 11:08:44 -07:00
.clang-format clang-format: add configuration file 2018-04-11 10:28:35 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap Merge branch 'asoc-4.17' into asoc-4.18 for compress dependencies 2018-04-26 12:24:28 +01:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS/CREDITS: Drop METAG ARCHITECTURE 2018-03-05 16:34:24 +00:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: add basic helper macros to scripts/Kconfig.include 2018-05-29 03:31:19 +09:00
MAINTAINERS MAINTAINERS: add an entry for MediaTek Bluetooth driver 2018-08-07 21:35:36 +02:00
Makefile Linux 4.18-rc8 2018-08-05 12:37:41 -07:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -06:00

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.