linux-kernel - Re: INFO: rcu_preempt detected expedited stalls on CPUs/tasks (6.1.0-rc3): in cat /sys/kernel/debug/kmemleak #forregzbot

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Date:   Wed, 9 Nov 2022 11:48:20 +0100
From:   Thorsten Leemhuis <regressions@...mhuis.info>
To:     "regressions@...ts.linux.dev" <regressions@...ts.linux.dev>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: INFO: rcu_preempt detected expedited stalls on CPUs/tasks
 (6.1.0-rc3): in cat /sys/kernel/debug/kmemleak #forregzbot

[Note: this mail is primarily send for documentation purposes and/or for
regzbot, my Linux kernel regression tracking bot. That's why I removed
most or all folks from the list of recipients, but left any that looked
like a mailing lists. These mails usually contain '#forregzbot' in the
subject, to make them easy to spot and filter out.]

[TLDR: I'm adding this regression report to the list of tracked
regressions; all text from me you find below is based on a few templates
paragraphs you might have encountered already already in similar form.]

Hi, this is your Linux kernel regression tracker.

On 04.11.22 23:01, Mirsad Goran Todorovac wrote:
> 
> When investigating thermald kmemleak, it occurred that the "cat
> /sys/kernel/debug/kmemleak"
> and "tail -20 /sys/kernel/debug/kmemleak" commands take unusual amount
> of time.
> 
> Dmesg output showed expedited stalls that the commands caused NMIs and
> NMI backtraces:
> 
> [ 8123.263464] rcu: INFO: rcu_preempt detected expedited stalls on
> CPUs/tasks: { 0-.... } 26 jiffies s: 3829 root: 0x1/.
> [ 8123.263500] rcu: blocking rcu_node structures (internal RCU debug):
> [ 8123.263508] Sending NMI from CPU 7 to CPUs 0:
> [ 8123.263528] NMI backtrace for cpu 0
> [ 8123.263539] CPU: 0 PID: 27898 Comm: cat Not tainted 6.1.0-rc3 #1
> [ 8123.263552] Hardware name: LENOVO 82H8/LNVNB161216, BIOS GGCN34WW
> 03/08/2022

#regzbot ^introduced 28b3ae426598e
#regzbot title rcu: thermald causes a kmemleak
#regzbot ignore-activity

This isn't a regression? This issue or a fix for it are already
discussed somewhere else? It was fixed already? You want to clarify when
the regression started to happen? Or point out I got the title or
something else totally wrong? Then just reply -- ideally with also
telling regzbot about it, as explained here:
https://linux-regtracking.leemhuis.info/tracked-regression/

Reminder for developers: When fixing the issue, add 'Link:' tags
pointing to the report (the mail this one replies to), as explained for
in the Linux kernel's documentation; above webpage explains why this is
important for tracked regressions.

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)

P.S.: As the Linux kernel's regression tracker I deal with a lot of
reports and sometimes miss something important when writing mails like
this. If that's the case here, don't hesitate to tell me in a public
reply, it's in everyone's interest to set the public record straight.