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Petr Mladek a68c246065 watchdog/softlockup: remove logic that tried to prevent repeated reports 
[ Upstream commit 1bc503cb4a ]

The softlockup detector does some gymnastic with the variable
soft_watchdog_warn.  It was added by the commit 58687acba5
("lockup_detector: Combine nmi_watchdog and softlockup detector").

The purpose is not completely clear.  There are the following clues.  They
describe the situation how it looked after the above mentioned commit:

  1. The variable was checked with a comment "only warn once".

  2. The variable was set when softlockup was reported. It was cleared
     only when the CPU was not longer in the softlockup state.

  3. watchdog_touch_ts was not explicitly updated when the softlockup
     was reported. Without this variable, the report would normally
     be printed again during every following watchdog_timer_fn()
     invocation.

The logic has got even more tangled up by the commit ed235875e2
("kernel/watchdog.c: print traces for all cpus on lockup detection").
After this commit, soft_watchdog_warn is set only when
softlockup_all_cpu_backtrace is enabled.  But multiple reports from all
CPUs are prevented by a new variable soft_lockup_nmi_warn.

Conclusion:

The variable probably never worked as intended.  In each case, it has not
worked last many years because the softlockup was reported repeatedly
after the full period defined by watchdog_thresh.

The reason is that watchdog gets touched in many known slow paths, for
example, in printk_stack_address().  This code is called also when
printing the softlockup report.  It means that the watchdog timestamp gets
updated after each report.

Solution:

Simply remove the logic. People want the periodic report anyway.

Link: https://lkml.kernel.org/r/20210311122130.6788-5-pmladek@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Laurence Oberman <loberman@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Whitchurch <vincent.whitchurch@axis.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2021-05-19 10:13:00 +02:00
arch ia64: module: fix symbolizer crash on fdescr 2021-05-19 10:12:59 +02:00
block block: return -EBUSY when there are open partitions in blkdev_reread_part 2021-04-28 13:39:59 +02:00
certs
crypto async_xor: increase src_offs when dropping destination page 2021-05-14 09:49:59 +02:00
Documentation kbuild: generate Module.symvers only when vmlinux exists 2021-05-19 10:12:59 +02:00
drivers bnxt_en: Add PCI IDs for Hyper-V VF devices. 2021-05-19 10:12:59 +02:00
fs cuse: prevent clone 2021-05-19 10:12:56 +02:00
include i2c: Add I2C_AQ_NO_REP_START adapter quirk 2021-05-19 10:12:54 +02:00
init seccomp: Fix CONFIG tests for Seccomp_filters 2021-05-14 09:50:24 +02:00
ipc
kernel watchdog/softlockup: remove logic that tried to prevent repeated reports 2021-05-19 10:13:00 +02:00
lib bug: Remove redundant condition check in report_bug 2021-05-14 09:50:32 +02:00
LICENSES
mm mm/memory-failure: unnecessary amount of unmapping 2021-05-14 09:50:45 +02:00
net net: sched: tapr: prevent cycle_time == 0 in parse_taprio_schedule 2021-05-19 10:12:57 +02:00
samples samples/bpf: Fix broken tracex1 due to kprobe argument change 2021-05-19 10:12:57 +02:00
scripts kbuild: generate Module.symvers only when vmlinux exists 2021-05-19 10:12:59 +02:00
security KEYS: trusted: Fix memory leak on object td 2021-05-19 10:12:50 +02:00
sound ASoC: rt286: Generalize support for ALC3263 codec 2021-05-19 10:12:57 +02:00
tools selftests: mlxsw: Fix mausezahn invocation in ERSPAN scale test 2021-05-19 10:12:59 +02:00
usr
virt kvm: Cap halt polling at kvm->max_halt_poll_ns 2021-05-19 10:12:51 +02:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore kbuild: generate Module.symvers only when vmlinux exists 2021-05-19 10:12:59 +02:00
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COPYING
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MAINTAINERS MAINTAINERS: move the staging subsystem to lists.linux.dev 2021-03-25 09:04:18 +01:00
Makefile kbuild: generate Module.symvers only when vmlinux exists 2021-05-19 10:12:59 +02:00
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.