Subject: Re: [PATCH] sched/deadline: stop dl_server before CPU goes offline

From: Youngmin Nam <[email-masked]>
Date: Fri, 17 Oct 2025 15:01:05 +0900

On Tue, Oct 14, 2025 at 11:11:31AM +0200, Juri Lelli wrote:
> Hello,
> 
> On 10/10/25 00:17, Shrikanth Hegde wrote:
> > From: Peter Zijlstra (Intel) <[email-masked]>
> > 
> > IBM CI tool reported kernel warning[1] when running a CPU removal
> > operation through drmgr[2]. i.e "drmgr -c cpu -r -q 1"
> > 
> > WARNING: CPU: 0 PID: 0 at kernel/sched/cpudeadline.c:219 cpudl_set+0x58/0x170
> > NIP [c0000000002b6ed8] cpudl_set+0x58/0x170
> > LR [c0000000002b7cb8] dl_server_timer+0x168/0x2a0
> > Call Trace:
> > [c000000002c2f8c0] init_stack+0x78c0/0x8000 (unreliable)
> > [c0000000002b7cb8] dl_server_timer+0x168/0x2a0
> > [c00000000034df84] __hrtimer_run_queues+0x1a4/0x390
> > [c00000000034f624] hrtimer_interrupt+0x124/0x300
> > [c00000000002a230] timer_interrupt+0x140/0x320
> > 
> > Git bisects to: commit 4ae8d9aa9f9d ("sched/deadline: Fix dl_server getting stuck")
> > 
> > This happens since: 
> > - dl_server hrtimer gets enqueued close to cpu offline, when 
> >   kthread_park enqueues a fair task.
> > - CPU goes offline and drmgr removes it from cpu_present_mask.
> > - hrtimer fires and warning is hit.
> > 
> > Fix it by stopping the dl_server before CPU is marked dead.
> > 
> > [1]: https://lore.kernel.org/all/[email-masked]/
> > [2]: https://github.com/ibm-power-utilities/powerpc-utils/tree/next/src/drmgr
> > 
> > [sshegde: wrote the changelog and tested it]
> > Fixes: 4ae8d9aa9f9d ("sched/deadline: Fix dl_server getting stuck")
> > Reported-by: Venkat Rao Bagalkote <[email-masked]>
> > Closes: https://lore.kernel.org/all/[email-masked]
> > Signed-off-by: Peter Zijlstra (Intel) <[email-masked]>
> > Signed-off-by: Shrikanth Hegde <[email-masked]>
> > Tested-by: Marek Szyprowski <[email-masked]>
> > Tested-by: Shrikanth Hegde <[email-masked]>
> 
> Looks good to me.
> 
> Acked-by: Juri Lelli <[email-masked]>
> 
> Thanks!
> Juri
> 

Hi All,

Could we expect this patch to address the following issue as well?

https://lore.kernel.org/all/[email-masked]/

Thanks,
Youngmin.