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Guilherme G. Piccoli 0ec9dc9bcb kernel/hung_task.c: introduce sysctl to print all traces when a hung task is detected 
Commit 401c636a0e ("kernel/hung_task.c: show all hung tasks before
panic") introduced a change in that we started to show all CPUs
backtraces when a hung task is detected _and_ the sysctl/kernel
parameter "hung_task_panic" is set.  The idea is good, because usually
when observing deadlocks (that may lead to hung tasks), the culprit is
another task holding a lock and not necessarily the task detected as
hung.

The problem with this approach is that dumping backtraces is a slightly
expensive task, specially printing that on console (and specially in
many CPU machines, as servers commonly found nowadays).  So, users that
plan to collect a kdump to investigate the hung tasks and narrow down
the deadlock definitely don't need the CPUs backtrace on dmesg/console,
which will delay the panic and pollute the log (crash tool would easily
grab all CPUs traces with 'bt -a' command).

Also, there's the reciprocal scenario: some users may be interested in
seeing the CPUs backtraces but not have the system panic when a hung
task is detected.  The current approach hence is almost as embedding a
policy in the kernel, by forcing the CPUs backtraces' dump (only) on
hung_task_panic.

This patch decouples the panic event on hung task from the CPUs
backtraces dump, by creating (and documenting) a new sysctl called
"hung_task_all_cpu_backtrace", analog to the approach taken on soft/hard
lockups, that have both a panic and an "all_cpu_backtrace" sysctl to
allow individual control.  The new mechanism for dumping the CPUs
backtraces on hung task detection respects "hung_task_warnings" by not
dumping the traces in case there's no warnings left.

Signed-off-by: Guilherme G. Piccoli <gpiccoli@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Link: http://lkml.kernel.org/r/20200327223646.20779-1-gpiccoli@canonical.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 		2020-06-08 11:05:56 -07:00
Documentation kernel/hung_task.c: introduce sysctl to print all traces when a hung task is detected 2020-06-08 11:05:56 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch Char/Misc driver patches for 5.8-rc1 2020-06-07 10:59:32 -07:00
block for-5.8/drivers-2020-06-01 2020-06-02 15:37:03 -07:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto crypto: engine - do not requeue in case of fatal error 2020-05-28 17:27:52 +10:00
drivers Char/Misc driver patches for 5.8-rc1 2020-06-07 10:59:32 -07:00
fs kernel/watchdog.c: convert {soft/hard}lockup boot parameters to sysctl aliases 2020-06-08 11:05:56 -07:00
include kernel/hung_task.c: introduce sysctl to print all traces when a hung task is detected 2020-06-08 11:05:56 -07:00
init kernel/sysctl: support setting sysctl parameters from kernel command line 2020-06-08 11:05:56 -07:00
ipc ipc/namespace.c: use a work queue to free_ipc 2020-06-08 11:05:56 -07:00
kernel kernel/hung_task.c: introduce sysctl to print all traces when a hung task is detected 2020-06-08 11:05:56 -07:00
lib lib/test_sysctl: support testing of sysctl. boot parameter 2020-06-08 11:05:56 -07:00
mm kernel/sysctl: support handling command line aliases 2020-06-08 11:05:56 -07:00
net Kbuild updates for v5.8 2020-06-06 12:00:25 -07:00
samples Kbuild updates for v5.8 2020-06-06 12:00:25 -07:00
scripts Fix for arch/sh build regression with newer binutils, removal of SH5, 2020-06-06 15:22:01 -07:00
security integrity-v5.8 2020-06-06 09:39:05 -07:00
sound powerpc updates for 5.8 2020-06-05 12:39:30 -07:00
tools lib/test_sysctl: support testing of sysctl. boot parameter 2020-06-08 11:05:56 -07:00
usr bpfilter: match bit size of bpfilter_umh to that of the kernel 2020-05-17 18:52:01 +09:00
virt A fair amount of stuff this time around, dominated by yet another massive 2020-06-01 15:45:27 -07:00
.clang-format block: add bio_for_each_bvec_all() 2020-05-25 11:25:24 +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 modpost: generate vmlinux.symvers and reuse it for the second modpost 2020-06-06 23:38:12 +09:00
.mailmap A fair amount of stuff this time around, dominated by yet another massive 2020-06-01 15:45:27 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS mailmap: change email for Ricardo Ribalda 2020-05-25 18:59:59 -06:00
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 Staging/IIO driver patches for 5.8-rc1 2020-06-07 10:45:08 -07:00
Makefile Kbuild updates for v5.8 2020-06-06 12:00:25 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

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.