On Tue, Oct 14, 2025 at 11:11:31AM +0200, Juri Lelli wrote:

Hello,

On 10/10/25 00:17, Shrikanth Hegde wrote:

quoted

From: Peter Zijlstra (Intel) <peterz@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/ (local)
[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 <redacted>
Closes: https://lore.kernel.org/all/8218e149-7718-4432-9312-f97297c352b9@linux.ibm.com (local)
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Shrikanth Hegde <redacted>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Shrikanth Hegde <redacted>

Looks good to me.

Acked-by: Juri Lelli <juri.lelli@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/ (local)

Thanks,
Youngmin.