linux-kernel - Re: [6.13-rc0 regression] workqueue throwing cpu affinity warnings during CPU hotplug

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Message-ID: <Z1ocEDhfwJ0Q-WYm@dread.disaster.area>
Date: Thu, 12 Dec 2024 10:11:12 +1100
From: Dave Chinner <david@...morbit.com>
To: Tejun Heo <tj@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org
Subject: Re: [6.13-rc0 regression] workqueue throwing cpu affinity warnings
 during CPU hotplug

On Wed, Dec 11, 2024 at 12:57:26PM -1000, Tejun Heo wrote:
> Hello, Dave.
> 
> Sorry about the really late reply.
> 
> On Fri, Nov 22, 2024 at 11:38:19AM +1100, Dave Chinner wrote:
> > Hi Tejun,
> > 
> > I just upgraded my test VMs from 6.12.0 to a current TOT kernel and
> > I got several of these warnings whilst running fstests whilst
> > running CPU hotplug online/offline concurrently with various tests:
> > 
> > [ 2508.109594] ------------[ cut here ]------------
> > [ 2508.115669] WARNING: CPU: 23 PID: 133 at kernel/kthread.c:76 kthread_set_per_cpu+0x33/0x50
> ...
> > [ 2508.253909]  <TASK>
> > [ 2508.311972]  unbind_worker+0x1b/0x70
> > [ 2508.315444]  workqueue_offline_cpu+0xd8/0x1f0
> > [ 2508.319554]  cpuhp_invoke_callback+0x13e/0x4f0
> > [ 2508.328936]  cpuhp_thread_fun+0xda/0x120
> > [ 2508.332746]  smpboot_thread_fn+0x132/0x1d0
> > [ 2508.336645]  kthread+0x147/0x170
> > [ 2508.347646]  ret_from_fork+0x3e/0x50
> > [ 2508.353845]  ret_from_fork_asm+0x1a/0x30
> > [ 2508.357773]  </TASK>
> > [ 2508.357776] ---[ end trace 0000000000000000 ]---
> 
> So, this is kthread saying that the thread passed to it doesn't have
> PF_KTHREAD set. There hasn't been any related changes and the flag is never
> cleared once set, so I don't see how that could be for a kworker.

....

> > I didn't see these on 6.12.0, so I'm guessing that there is
> > something in the merge window that has started triggering this.
> 
> I tried a few mixtures of stress-ng + continuous hot [un]plugging but can't
> reproduce in the current linus#master. Do you still see this happening?

I don't know. The machine that I was using to reproduce this has
been down with hardware failure for the last two weeks. I might have
it back up today, and then I'll be able to start exercising this
again.

-Dave.

-- 
Dave Chinner
david@...morbit.com