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

[Juri Lelli]

On 17/10/25 15:01, Youngmin Nam wrote:
> 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) <peterz at infradead.org>
> > > 
> > > 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/8218e149-7718-4432-9312-f97297c352b9@linux.ibm.com/
> > > [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 <venkat88 at linux.ibm.com>
> > > Closes: https://lore.kernel.org/all/8218e149-7718-4432-9312-f97297c352b9@linux.ibm.com
> > > Signed-off-by: Peter Zijlstra (Intel) <peterz at infradead.org>
> > > Signed-off-by: Shrikanth Hegde <sshegde at linux.ibm.com>
> > > Tested-by: Marek Szyprowski <m.szyprowski at samsung.com>
> > > Tested-by: Shrikanth Hegde <sshegde at linux.ibm.com>
> > 
> > Looks good to me.
> > 
> > Acked-by: Juri Lelli <juri.lelli at redhat.com>
> > 
> > Thanks!
> > Juri
> > 
> 
> Hi All,
> 
> Could we expect this patch to address the following issue as well?
> 
> https://lore.kernel.org/all/aMKTHKfegBk4DgjA@jlelli-thinkpadt14gen4.remote.csb/

I don't think I see a direct connection with it.

Thanks,
Juri