Re: [PATCH v2 4/5] workqueue: Show all busy workers in stall diagnostics

[Jiri Slaby]

Hi,

we currently have several reports of this. On s390, ppc64, and x86_64.

On 07. 05. 26, 15:11, Breno Leitao wrote:
> Hi Jiri,
>
> On Thu, May 07, 2026 at 12:20:33PM +0200, Jiri Slaby wrote:
> > On 05. 03. 26, 17:15, Breno Leitao wrote:
> >
> >    BUG: workqueue lockup - pool cpus=144 node=0 flags=0x4 nice=0 stuck for
> > 168224s!
>
> That's an extremely long stall (~1.95 days).
>
> > ...
> >    Showing busy workqueues and worker pools:
> >    workqueue rcu_gp: flags=0x108
> >      pwq 578: cpus=144 node=0 flags=0x4 nice=0 active=3 refcnt=4
> > in:
> >    https://bugzilla.suse.com/show_bug.cgi?id=1263947
> > ?
> >
> > Can this (or other patch from the series) cause this? Should there be
> > something like cpu_online() instead of task_is_running() somewhere?
>
> This series only affects stall reporting, not detection. The changes run
> after the watchdog has identified a stall, so the detection logic itself
> remains unchanged.
>
> To help diagnose this issue, could you provide some additional information:
>
> 1) Was CPU 144 online at any point? If so, when was it taken offline?

It was not, it's non-present.

> 2) Does this message appear repeatedly? If you bring CPU 144 online, does
>     the issue resolve?

Yes, look at this new x86_64 report's dmesg (I believe it is related to 
the above report):
  BUG: workqueue lockup - pool cpus=2 node=0 flags=0x4 nice=0 stuck for 
50s!
in:
  https://bugzilla.suse.com/attachment.cgi?id=890229

$ grep -c BUG sl.txt
504
$ grep -c pwq sl.txt
509

It comes from:
https://bugzilla.suse.com/show_bug.cgi?id=1264554

> 3) Have you run similar tests on earlier kernel versions without seeing
>     this behavior, or is this a clear regression?

It's new in 7.0. Going back to 6.19.12 makes it disappear.

thanks,
--
js
suse labs