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John Stultz 295f3fcaa8 pstore: Revert pmsg_lock back to a normal mutex 
[ Upstream commit 5239a89b06 ]

This reverts commit 76d62f24db.

So while priority inversion on the pmsg_lock is an occasional
problem that an rt_mutex would help with, in uses where logging
is writing to pmsg heavily from multiple threads, the pmsg_lock
can be heavily contended.

After this change landed, it was reported that cases where the
mutex locking overhead was commonly adding on the order of 10s
of usecs delay had suddenly jumped to ~msec delay with rtmutex.

It seems the slight differences in the locks under this level
of contention causes the normal mutexes to utilize the spinning
optimizations, while the rtmutexes end up in the sleeping
slowpath (which allows additional threads to pile on trying
to take the lock).

In this case, it devolves to a worse case senerio where the lock
acquisition and scheduling overhead dominates, and each thread
is waiting on the order of ~ms to do ~us of work.

Obviously, having tons of threads all contending on a single
lock for logging is non-optimal, so the proper fix is probably
reworking pstore pmsg to have per-cpu buffers so we don't have
contention.

Additionally, Steven Rostedt has provided some furhter
optimizations for rtmutexes that improves the rtmutex spinning
path, but at least in my testing, I still see the test tripping
into the sleeping path on rtmutexes while utilizing the spinning
path with mutexes.

But in the short term, lets revert the change to the rt_mutex
and go back to normal mutexes to avoid a potentially major
performance regression. And we can work on optimizations to both
rtmutexes and finer-grained locking for pstore pmsg in the
future.

Cc: Wei Wang <wvw@google.com>
Cc: Midas Chien<midaschieh@google.com>
Cc: "Chunhui Li (李春辉)" <chunhui.li@mediatek.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Anton Vorontsov <anton@enomsg.org>
Cc: "Guilherme G. Piccoli" <gpiccoli@igalia.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: kernel-team@android.com
Fixes: 76d62f24db ("pstore: Switch pmsg_lock to an rt_mutex to avoid priority inversion")
Reported-by: "Chunhui Li (李春辉)" <chunhui.li@mediatek.com>
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230308204043.2061631-1-jstultz@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
2023-05-11 23:00:31 +09:00
arch arm64: kgdb: Set PSTATE.SS to 1 to re-enable single-step 2023-05-11 23:00:24 +09:00
block blk-crypto: make blk_crypto_evict_key() more robust 2023-05-11 23:00:16 +09:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:22:01 +02:00
crypto crypto: drbg - Only fail when jent is unavailable in FIPS mode 2023-05-11 23:00:27 +09:00
Documentation riscv: Move early dtb mapping into the fixmap region 2023-05-01 08:23:24 +09:00
drivers drivers: staging: rtl8723bs: Fix locking in rtw_scan_timeout_handler() 2023-05-11 23:00:31 +09:00
fs pstore: Revert pmsg_lock back to a normal mutex 2023-05-11 23:00:31 +09:00
include netfilter: nf_tables: don't write table validation state without mutex 2023-05-11 23:00:30 +09:00
init kbuild: Add CONFIG_PAHOLE_VERSION 2023-02-25 12:06:45 +01:00
io_uring io_uring: avoid null-ptr-deref in io_arm_poll_handler 2023-03-22 13:31:37 +01:00
ipc ipc/sem: Fix dangling sem_array access in semtimedop race 2022-12-08 11:28:45 +01:00
kernel bpf: Don't EFAULT for getsockopt with optval=NULL 2023-05-11 23:00:30 +09:00
lib debugobject: Prevent init race with static objects 2023-05-11 23:00:25 +09:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm writeback, cgroup: fix null-ptr-deref write in bdi_split_work_to_wbs 2023-05-11 23:00:18 +09:00
net tcp/udp: Fix memleaks of sk and zerocopy skbs with TX timestamp. 2023-05-11 23:00:31 +09:00
samples samples: vfio-mdev: Fix missing pci_disable_device() in mdpy_fb_probe() 2022-12-31 13:14:31 +01:00
scripts ASN.1: Fix check for strdup() success 2023-04-26 13:51:56 +02:00
security selinux: ensure av_permissions.h is built when needed 2023-05-11 23:00:19 +09:00
sound sound/oss/dmasound: fix build when drivers are mixed =y/=m 2023-05-11 23:00:19 +09:00
tools selftests/bpf: Fix leaked bpf_link in get_stackid_cannot_attach 2023-05-11 23:00:28 +09:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:27:15 +01:00
virt KVM: fix memoryleak in kvm_init() 2023-03-17 08:49:04 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes
.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
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild
Kconfig
MAINTAINERS counter: Internalize sysfs interface code 2023-04-20 12:13:55 +02:00
Makefile Linux 5.15.110 2023-05-01 08:23:24 +09:00
README

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.