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Arjun Roy 435ccfa894 tcp: Prevent low rmem stalls with SO_RCVLOWAT.
With SO_RCVLOWAT, under memory pressure,
it is possible to enter a state where:

1. We have not received enough bytes to satisfy SO_RCVLOWAT.
2. We have not entered buffer pressure (see tcp_rmem_pressure()).
3. But, we do not have enough buffer space to accept more packets.

In this case, we advertise 0 rwnd (due to #3) but the application does
not drain the receive queue (no wakeup because of #1 and #2) so the
flow stalls.

Modify the heuristic for SO_RCVLOWAT so that, if we are advertising
rwnd<=rcv_mss, force a wakeup to prevent a stall.

Without this patch, setting tcp_rmem to 6143 and disabling TCP
autotune causes a stalled flow. With this patch, no stall occurs. This
is with RPC-style traffic with large messages.

Fixes: 03f45c883c ("tcp: avoid extra wakeups for SO_RCVLOWAT users")
Signed-off-by: Arjun Roy <arjunroy@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20201023184709.217614-1-arjunroy.kdev@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2020-10-23 19:11:20 -07:00
arch ARM: 2020-10-23 11:17:56 -07:00
block docs: bio: fix a kerneldoc markup 2020-10-15 07:49:48 +02:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto drivers-5.10-2020-10-12 2020-10-13 13:04:41 -07:00
Documentation Fixes for 5.10-rc1 from the networking tree: 2020-10-23 12:05:49 -07:00
drivers net: ucc_geth: Drop extraneous parentheses in comparison 2020-10-23 18:44:06 -07:00
fs Changes in gfs2: 2020-10-23 11:47:42 -07:00
include Fixes for 5.10-rc1 from the networking tree: 2020-10-23 12:05:49 -07:00
init linux-kselftest-kunit-5.10-rc1 2020-10-18 14:45:59 -07:00
ipc ipc: adjust proc_ipc_sem_dointvec definition to match prototype 2020-09-05 12:14:29 -07:00
kernel Fixes for 5.10-rc1 from the networking tree: 2020-10-23 12:05:49 -07:00
lib Kbuild updates for v5.10 2020-10-22 13:13:57 -07:00
LICENSES LICENSES/deprecated: add Zlib license text 2020-09-16 14:33:49 +02:00
mm Refactored code for 5.10: 2020-10-23 11:33:41 -07:00
net tcp: Prevent low rmem stalls with SO_RCVLOWAT. 2020-10-23 19:11:20 -07:00
samples bpf, libbpf: Guard bpf inline asm from bpf_tail_call_static 2020-10-22 01:46:52 +02:00
scripts Fixes for 5.10-rc1 from the networking tree: 2020-10-23 12:05:49 -07:00
security task_work: cleanup notification modes 2020-10-17 15:05:30 -06:00
sound dma-mapping updates for 5.10 2020-10-15 14:43:29 -07:00
tools Fixes for 5.10-rc1 from the networking tree: 2020-10-23 12:05:49 -07:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt kvm: x86/mmu: Support dirty logging for the TDP MMU 2020-10-23 03:42:13 -04:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig
.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 .gitignore: docs: ignore sphinx_*/ directories 2020-09-10 10:44:31 -06:00
.mailmap MAINTAINERS: jarkko.sakkinen@linux.intel.com -> jarkko@kernel.org 2020-10-16 11:11:19 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS networking changes for the 5.10 merge window 2020-10-15 18:42:13 -07:00
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 Fixes for 5.10-rc1 from the networking tree: 2020-10-23 12:05:49 -07:00
Makefile Kbuild updates for v5.10 2020-10-22 13:13:57 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -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.

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.