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Paul E. McKenney 1ec0cd3b2c rcu: Don't deboost before reporting expedited quiescent state
commit 10c5357874 upstream.

Currently rcu_preempt_deferred_qs_irqrestore() releases rnp->boost_mtx
before reporting the expedited quiescent state.  Under heavy real-time
load, this can result in this function being preempted before the
quiescent state is reported, which can in turn prevent the expedited grace
period from completing.  Tim Murray reports that the resulting expedited
grace periods can take hundreds of milliseconds and even more than one
second, when they should normally complete in less than a millisecond.

This was fine given that there were no particular response-time
constraints for synchronize_rcu_expedited(), as it was designed
for throughput rather than latency.  However, some users now need
sub-100-millisecond response-time constratints.

This patch therefore follows Neeraj's suggestion (seconded by Tim and
by Uladzislau Rezki) of simply reversing the two operations.

Reported-by: Tim Murray <timmurray@google.com>
Reported-by: Joel Fernandes <joelaf@google.com>
Reported-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Reviewed-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Tested-by: Tim Murray <timmurray@google.com>
Cc: Todd Kjos <tkjos@google.com>
Cc: Sandeep Patil <sspatil@google.com>
Cc: <stable@vger.kernel.org> # 5.4.x
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2023-04-19 17:46:25 +08:00
arch ACPI / x86: Work around broken XSDT on Advantech DAC-BJ01 board 2023-04-19 17:46:24 +08:00
block block: release rq qos structures for queue without disk 2023-04-19 17:46:21 +08:00
certs certs: Add support for using elliptic curve keys for signing modules 2021-08-23 19:55:42 +03:00
crypto crypto: api - Move cryptomgr soft dependency into algapi 2023-04-19 17:45:10 +08:00
Documentation swiotlb: rework "fix info leak with DMA_FROM_DEVICE" 2023-04-19 17:46:16 +08:00
drivers drm/virtio: Ensure that objs is not NULL in virtio_gpu_array_put_free() 2023-04-19 17:46:25 +08:00
fs btrfs: skip reserved bytes warning on unmount after log cleanup failure 2023-04-19 17:46:23 +08:00
include ALSA: pcm: Fix races among concurrent hw_params and hw_free calls 2023-04-19 17:46:24 +08:00
init init: make unknown command line param message clearer 2023-04-19 16:57:51 +08:00
ipc ipc/sem: do not sleep with a spin lock held 2023-04-19 17:45:01 +08:00
kernel rcu: Don't deboost before reporting expedited quiescent state 2023-04-19 17:46:25 +08:00
lib ARM: 9178/1: fix unmet dependency on BITREVERSE for HAVE_ARCH_BITREVERSE 2023-04-19 17:46:19 +08:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm: swap: get rid of livelock in swapin readahead 2023-04-19 17:46:20 +08:00
net netfilter: nf_tables: validate registers coming from userspace. 2023-04-19 17:46:24 +08:00
samples samples: bpf: Fix 'unknown warning group' build warning on Clang 2023-04-19 17:43:59 +08:00
scripts kconfig: fix failing to generate auto.conf 2023-04-19 17:45:35 +08:00
security selinux: fix misuse of mutex_is_locked() 2023-04-19 17:45:37 +08:00
sound ALSA: pci: fix reading of swapped values from pcmreg in AC97 codec 2023-04-19 17:46:24 +08:00
tools perf symbols: Fix symbol size calculation condition 2023-04-19 17:46:22 +08:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2023-04-19 17:44:58 +08:00
virt KVM: Fix lockdep false negative during host resume 2023-04-19 17:46:14 +08:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.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 .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
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: adjust file entry for of_net.c after movement 2023-04-19 17:46:04 +08:00
Makefile Linux 5.15.31 2023-04-19 17:46:23 +08:00
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.