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Filename Latest commit message Latest commit date
Neal Cardwell f79de6451e tcp: fix indefinite deferral of RTO with SACK reneging
[ Upstream commit 3d2af9cce3133b3bc596a9d065c6f9d93419ccfb ]

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 23:56:55 +09:00
arch x86/unwind/orc: Fix unreliable stack dump with gcov 2022-11-03 23:56:55 +09:00
block blk-mq: don't create hctx debugfs dir until q->debugfs_dir is created 2022-08-25 11:17:36 +02:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:11:22 +02:00
crypto crypto: akcipher - default implementation for setting a private key 2022-10-26 13:22:45 +02:00
Documentation arm64: errata: Remove AES hwcap for COMPAT tasks 2022-10-29 10:20:35 +02:00
drivers net: lantiq_etop: don't free skb when returning NETDEV_TX_BUSY 2022-11-03 23:56:55 +09:00
fs xfs: force the log after remapping a synchronous-writes file 2022-11-03 23:56:54 +09:00
include media: v4l2: Fix v4l2_i2c_subdev_set_name function documentation 2022-11-03 23:56:54 +09:00
init random: handle latent entropy and command line from random_init() 2022-06-22 14:11:17 +02:00
ipc
kernel cgroup-v1: add disabled controller check in cgroup1_parse_param() 2022-11-03 23:56:54 +09:00
lib dyndbg: let query-modname override actual module name 2022-10-26 13:22:37 +02:00
LICENSES
mm mm,hugetlb: take hugetlb_lock before decrementing h->resv_huge_pages 2022-11-03 23:56:54 +09:00
net tcp: fix indefinite deferral of RTO with SACK reneging 2022-11-03 23:56:55 +09:00
samples
scripts kbuild: remove the target in signal traps when interrupted 2022-10-26 13:22:46 +02:00
security efi: Correct Macmini DMI match in uefi cert quirk 2022-10-15 07:54:39 +02:00
sound ALSA: ac97: fix possible memory leak in snd_ac97_dev_register() 2022-11-03 23:56:55 +09:00
tools perf auxtrace: Fix address filter symbol name match for modules 2022-11-03 23:56:54 +09:00
usr
virt KVM: arm64: vgic: Fix exit condition in scan_its_table() 2022-10-29 10:20:35 +02:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS MAINTAINERS: add Chandan as xfs maintainer for 5.4.y 2022-09-28 11:03:58 +02:00
Makefile Linux 5.4.222 2022-11-01 19:06:42 +01:00
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.