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authorGuilherme G. Piccoli <gpiccoli@canonical.com>2020-06-08 07:40:45 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2020-06-08 21:05:56 +0300
commit0ec9dc9bcba0a62b0844e54c1caf6b8b0bf6b5b4 (patch)
tree4f943adb6612e5161748b68437650507e78643d2 /Documentation
parentf117955a2255721a6a0e9cecf6cad3a6eb43cbc3 (diff)
downloadlinux-0ec9dc9bcba0a62b0844e54c1caf6b8b0bf6b5b4.tar.xz
kernel/hung_task.c: introduce sysctl to print all traces when a hung task is detected
Commit 401c636a0eeb ("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>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/admin-guide/sysctl/kernel.rst14
1 files changed, 14 insertions, 0 deletions
diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 3b00b9223157..861820d27c19 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -335,6 +335,20 @@ Path for the hotplug policy agent.
Default value is "``/sbin/hotplug``".
+hung_task_all_cpu_backtrace:
+================
+
+If this option is set, the kernel will send an NMI to all CPUs to dump
+their backtraces when a hung task is detected. This file shows up if
+CONFIG_DETECT_HUNG_TASK and CONFIG_SMP are enabled.
+
+0: Won't show all CPUs backtraces when a hung task is detected.
+This is the default behavior.
+
+1: Will non-maskably interrupt all CPUs and dump their backtraces when
+a hung task is detected.
+
+
hung_task_panic
===============