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Filename Latest commit message Latest commit date
Neal Cardwell ff81628202 tcp: fix to allow timestamp undo if no retransmits were sent
[ Upstream commit e37ab7373696e650d3b6262a5b882aadad69bb9e ]

Fix the TCP loss recovery undo logic in tcp_packet_delayed() so that
it can trigger undo even if TSQ prevents a fast recovery episode from
reaching tcp_retransmit_skb().

Geumhwan Yu <geumhwan.yu@samsung.com> recently reported that after
this commit from 2019:

commit bc9f38c832 ("tcp: avoid unconditional congestion window undo
on SYN retransmit")

...and before this fix we could have buggy scenarios like the
following:

+ Due to reordering, a TCP connection receives some SACKs and enters a
  spurious fast recovery.

+ TSQ prevents all invocations of tcp_retransmit_skb(), because many
  skbs are queued in lower layers of the sending machine's network
  stack; thus tp->retrans_stamp remains 0.

+ The connection receives a TCP timestamp ECR value echoing a
  timestamp before the fast recovery, indicating that the fast
  recovery was spurious.

+ The connection fails to undo the spurious fast recovery because
  tp->retrans_stamp is 0, and thus tcp_packet_delayed() returns false,
  due to the new logic in the 2019 commit: commit bc9f38c832 ("tcp:
  avoid unconditional congestion window undo on SYN retransmit")

This fix tweaks the logic to be more similar to the
tcp_packet_delayed() logic before bc9f38c832, except that we take
care not to be fooled by the FLAG_SYN_ACKED code path zeroing out
tp->retrans_stamp (the bug noted and fixed by Yuchung in
bc9f38c832).

Note that this returns the high-level behavior of tcp_packet_delayed()
to again match the comment for the function, which says: "Nothing was
retransmitted or returned timestamp is less than timestamp of the
first retransmission." Note that this comment is in the original
2005-04-16 Linux git commit, so this is evidently long-standing
behavior.

Fixes: bc9f38c832 ("tcp: avoid unconditional congestion window undo on SYN retransmit")
Reported-by: Geumhwan Yu <geumhwan.yu@samsung.com>
Diagnosed-by: Geumhwan Yu <geumhwan.yu@samsung.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>
Link: https://patch.msgid.link/20241001200517.2756803-2-ncardwell.sw@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2024-11-08 16:20:45 +01:00
arch s390/cpum_sf: Remove WARN_ON_ONCE statements 2024-11-08 16:20:44 +01:00
block block, bfq: don't break merge chain in bfq_split_bfqq() 2024-11-08 16:20:28 +01:00
certs
crypto crypto: aead,cipher - zeroize key buffer after use 2024-11-08 16:20:33 +01:00
Documentation arm64: errata: Expand speculative SSBS workaround once more 2024-11-08 16:20:42 +01:00
drivers ice: fix VLAN replay after reset 2024-11-08 16:20:45 +01:00
fs SUNRPC: Fix integer overflow in decode_rc_list() 2024-11-08 16:20:45 +01:00
include media: uapi/linux/cec.h: cec_msg_set_reply_to: zero flags 2024-11-08 16:20:41 +01:00
init init: open /initrd.image with O_LARGEFILE 2024-04-13 12:51:36 +02:00
ipc ipc: replace costly bailout check in sysvipc_find_ipc() 2024-09-04 13:15:02 +02:00
kernel bpf: Check percpu map value size first 2024-11-08 16:20:44 +01:00
lib debugobjects: Fix conditions in fill_pool() 2024-11-08 16:20:34 +01:00
LICENSES
mm mm: krealloc: consider spare memory for __GFP_ZERO 2024-11-08 16:20:40 +01:00
net tcp: fix to allow timestamp undo if no retransmits were sent 2024-11-08 16:20:45 +01:00
samples media: rename VFL_TYPE_GRABBER to _VIDEO 2024-03-26 18:22:22 -04:00
scripts scripts: kconfig: merge_config: config files: add a trailing newline 2024-11-08 16:20:24 +01:00
security tomoyo: fallback to realpath if symlink's pathname does not exist 2024-11-08 16:20:41 +01:00
sound ALSA: core: add isascii() check to card ID generator 2024-11-08 16:20:40 +01:00
tools tools/iio: Add memory allocation failure check for trigger_name 2024-11-08 16:20:45 +01:00
usr
virt KVM: async_pf: Cleanup kvm_setup_async_pf() 2024-05-02 16:18:32 +02:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore Remove *.orig pattern from .gitignore 2024-11-08 16:20:33 +01:00
.mailmap
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS iio: stx104: Move to addac subdirectory 2023-08-30 16:27:12 +02:00
Makefile Linux 5.4.284 2024-09-12 11:03:57 +02:00
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.