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Tags: kernel   lockup   watchdog   scheduler  
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Title: rcu_sched self-detected stall on CPU + watchdog: BUG: soft lockup - CPU#3 stuck for 22s
ID: /2019/02/16/rcu_sched-self-detected-stall-on-CPU-_-watchdog_-BUG_-soft-lockup-CPU_3-stuck-for-22s
Created: February 16, 2019
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From: What are all these “Bug: soft lockup” messages about?


In the system log (/var/log/messages or journalctl) a lot of the
following messages is printed.

May 25 07:23:59 XXXXXXX kernel: [13445315.881356] BUG: soft lockup - CPU#16 stuck for 23s! [yyyyyyy:81602]  

followed by various stack traces. This document tries to explain what
the soft lockup messages mean.

The error message itself doesn’t tell you what is causing the problem.


A ‘soft lockup’ is defined as a bug that causes the kernel to loop in
kernel mode for more than 20 seconds, without giving other tasks a
chance to run. The watchdog daemon will send an non maskable interrupt
(NMI) to all CPUs in the system who in turn print the stack traces of
their currently running tasks.

Reducing server load is normal solution:


Under normal circumstances those messages may go away if the load
decreased. This ‘soft lockup’ can happen if the kernel is busy,
working on a huge amount of objects which need to be scanned, freed or
allocated respectively. The stack traces of those tasks can give a
first idea what the tasks were doing. However, to be able to examine
the cause behind the messages, a kernel dump would be needed.

You cannot disable those messages, however in some situations
increasing the time when those soft lockups will be fired can relax
the situation.

Do do so just increase the following sysctl parameter:
kernel.watchdog_thresh Default value for this parameter is 10 and
to double the value might be a good start.

⇧ How much is too many zombies (bad) Resetting Ubuntu to factory settings  ⇩