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Neal Cardwell 1634d5d39c tcp: fix indefinite deferral of RTO with SACK reneging [ Upstream commit `3d2af9cce3` ] This commit fixes a bug that can cause a TCP data sender to repeatedly defer RTOs when encountering SACK reneging. The bug is that when we're in fast recovery in a scenario with SACK reneging, every time we get an ACK we call tcp_check_sack_reneging() and it can note the apparent SACK reneging and rearm the RTO timer for srtt/2 into the future. In some SACK reneging scenarios that can happen repeatedly until the receive window fills up, at which point the sender can't send any more, the ACKs stop arriving, and the RTO fires at srtt/2 after the last ACK. But that can take far too long (O(10 secs)), since the connection is stuck in fast recovery with a low cwnd that cannot grow beyond ssthresh, even if more bandwidth is available. This fix changes the logic in tcp_check_sack_reneging() to only rearm the RTO timer if data is cumulatively ACKed, indicating forward progress. This avoids this kind of nearly infinite loop of RTO timer re-arming. In addition, this meets the goals of tcp_check_sack_reneging() in handling Windows TCP behavior that looks temporarily like SACK reneging but is not really. Many thanks to Jakub Kicinski and Neil Spring, who reported this issue and provided critical packet traces that enabled root-causing this issue. Also, many thanks to Jakub Kicinski for testing this fix. Fixes: `5ae344c949` ("tcp: reduce spurious retransmits due to transient SACK reneging") Reported-by: Jakub Kicinski <kuba@kernel.org> Reported-by: Neil Spring <ntspring@fb.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Cc: Yuchung Cheng <ycheng@google.com> Tested-by: Jakub Kicinski <kuba@kernel.org> Link: https://lore.kernel.org/r/20221021170821.1093930-1-ncardwell.kernel@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>		2022-11-03 23:57:52 +09:00
arch	x86/unwind/orc: Fix unreliable stack dump with gcov	2022-11-03 23:57:51 +09:00
block	blk-wbt: fix that 'rwb->wc' is always set to 1 in wbt_init()	2022-10-30 09:41:19 +01:00
certs	certs/blacklist_hashes.c: fix const confusion in certs blacklist	2022-06-22 14:13:17 +02:00
crypto	crypto: akcipher - default implementation for setting a private key	2022-10-26 13:25:42 +02:00
Documentation	arm64: errata: Remove AES hwcap for COMPAT tasks	2022-10-30 09:41:16 +01:00
drivers	net: lantiq_etop: don't free skb when returning NETDEV_TX_BUSY	2022-11-03 23:57:52 +09:00
fs	kernfs: fix use-after-free in __kernfs_remove	2022-11-03 23:57:50 +09:00
include	media: v4l2: Fix v4l2_i2c_subdev_set_name function documentation	2022-11-03 23:57:51 +09:00
init	Kconfig: Add option for asm goto w/ tied outputs to workaround clang-13 bug	2022-06-09 10:21:25 +02:00
ipc	ipc/mqueue: use get_tree_nodev() in mqueue_get_tree()	2022-06-09 10:21:17 +02:00
kernel	tracing: Do not free snapshot if tracer is on cmdline	2022-10-30 09:41:18 +01:00
lib	dyndbg: drop EXPORTed dynamic_debug_exec_queries	2022-10-26 13:25:34 +02:00
LICENSES	LICENSES/deprecated: add Zlib license text	2020-09-16 14:33:49 +02:00
mm	mm,hugetlb: take hugetlb_lock before decrementing h->resv_huge_pages	2022-11-03 23:57:50 +09:00
net	tcp: fix indefinite deferral of RTO with SACK reneging	2022-11-03 23:57:52 +09:00
samples	x86: Prepare inline-asm for straight-line-speculation	2022-07-25 11:26:29 +02:00
scripts	kbuild: Add skip_encoding_btf_enum64 option to pahole	2022-10-28 12:57:12 +02:00
security	selinux: enable use of both GFP_KERNEL and GFP_ATOMIC in convert_context()	2022-10-30 09:41:15 +01:00
sound	ALSA: ac97: fix possible memory leak in snd_ac97_dev_register()	2022-11-03 23:57:51 +09:00
tools	perf auxtrace: Fix address filter symbol name match for modules	2022-11-03 23:57:50 +09:00
usr	usr/include/Makefile: add linux/nfc.h to the compile-test coverage	2022-02-01 17:25:48 +01:00
virt	kvm: Add support for arch compat vm ioctls	2022-10-30 09:41:15 +01:00
.clang-format	RDMA 5.10 pull request	2020-10-17 11:18:18 -07:00
.cocciconfig	scripts: add Linux .cocciconfig for coccinelle	2016-07-22 12:13:39 +02:00
.get_maintainer.ignore	Opt out of scripts/get_maintainer.pl	2019-05-16 10:53:40 -07:00
.gitattributes	.gitattributes: use 'dts' diff driver for dts files	2019-12-04 19:44:11 -08:00
.gitignore	kbuild: generate Module.symvers only when vmlinux exists	2021-05-19 10:12:59 +02:00
.mailmap	mailmap: add two more addresses of Uwe Kleine-König	2020-12-06 10:19:07 -08:00
COPYING	COPYING: state that all contributions really are covered by this file	2020-02-10 13:32:20 -08:00
CREDITS	MAINTAINERS: Move Jason Cooper to CREDITS	2020-11-30 10:20:34 +01:00
Kbuild	kbuild: rename hostprogs-y/always to hostprogs/always-y	2020-02-04 01:53:07 +09:00
Kconfig	kbuild: ensure full rebuild when the compiler is updated	2020-05-12 13:28:33 +09:00
MAINTAINERS	MAINTAINERS: add Amir as xfs maintainer for 5.10.y	2022-07-02 16:39:22 +02:00
Makefile	Linux 5.10.152	2022-10-30 09:41:19 +01:00
README	Drop all 00-INDEX files from Documentation/	2018-09-09 15:08:58 -06:00

README

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.

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.