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Filename Latest commit message Latest commit date
Eric Dumazet 774bacf121 tcp: fix SO_RCVLOWAT related hangs under mem pressure
[ Upstream commit f969dc5a885736842c3511ecdea240fbb02d25d9 ]

While commit 24adbc1676af ("tcp: fix SO_RCVLOWAT hangs with fat skbs")
fixed an issue vs too small sk_rcvbuf for given sk_rcvlowat constraint,
it missed to address issue caused by memory pressure.

1) If we are under memory pressure and socket receive queue is empty.
First incoming packet is allowed to be queued, after commit
76dfa60820 ("tcp: allow one skb to be received per socket under memory pressure")

But we do not send EPOLLIN yet, in case tcp_data_ready() sees sk_rcvlowat
is bigger than skb length.

2) Then, when next packet comes, it is dropped, and we directly
call sk->sk_data_ready().

3) If application is using poll(), tcp_poll() will then use
tcp_stream_is_readable() and decide the socket receive queue is
not yet filled, so nothing will happen.

Even when sender retransmits packets, phases 2) & 3) repeat
and flow is effectively frozen, until memory pressure is off.

Fix is to consider tcp_under_memory_pressure() to take care
of global memory pressure or memcg pressure.

Fixes: 24adbc1676af ("tcp: fix SO_RCVLOWAT hangs with fat skbs")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Arjun Roy <arjunroy@google.com>
Suggested-by: Wei Wang <weiwan@google.com>
Reviewed-by: Wei Wang <weiwan@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2021-03-04 10:26:17 +01:00
arch arm64: dts: msm8916: Fix reserved and rfsa nodes unit address 2021-03-04 10:26:16 +01:00
block bfq: Avoid false bfq queue merging 2021-03-04 10:26:10 +01:00
certs
crypto crypto: asym_tpm: correct zero out potential secrets 2021-01-12 20:16:17 +01:00
Documentation KVM: Forbid the use of tagged userspace addresses for memslots 2021-02-03 23:25:57 +01:00
drivers xen/netback: fix spurious event detection for common event case 2021-03-04 10:26:17 +01:00
fs debugfs: do not attempt to create a new file before the filesystem is initalized 2021-03-04 10:26:10 +01:00
include tcp: fix SO_RCVLOWAT related hangs under mem pressure 2021-03-04 10:26:17 +01:00
init fgraph: Initialize tracing_graph_pause at task creation 2021-02-10 09:25:29 +01:00
ipc
kernel bpf_lru_list: Read double-checked variable once without lock 2021-03-04 10:26:16 +01:00
lib udp: fix skb_copy_and_csum_datagram with odd segment sizes 2021-02-17 10:35:19 +01:00
LICENSES
mm mm: provide a saner PTE walking API for modules 2021-02-26 10:10:28 +01:00
net bpf: Fix bpf_fib_lookup helper MTU check for SKB ctx 2021-03-04 10:26:17 +01:00
samples samples: bpf: Fix lwt_len_hist reusing previous BPF map 2020-12-30 11:51:12 +01:00
scripts scripts/recordmcount.pl: support big endian for ARCH sh 2021-02-26 10:10:28 +01:00
security cap: fix conversions on getxattr 2021-02-17 10:35:15 +01:00
sound ALSA: usb-audio: Fix PCM buffer allocation in non-vmalloc mode 2021-03-04 10:26:10 +01:00
tools selftests: txtimestamp: fix compilation issue 2021-02-17 10:35:17 +01:00
usr
virt KVM: Use kvm_pfn_t for local PFN variable in hva_to_pfn_remapped() 2021-02-26 10:10:28 +01:00
.clang-format
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COPYING
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Kbuild
Kconfig
MAINTAINERS
Makefile Linux 5.4.101 2021-02-26 10:10:28 +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.