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

[Juri Lelli <juri.lelli@redhat.com>]

Hello,

On 10/10/25 00:17, Shrikanth Hegde wrote:
> 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/
> [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@linux.ibm.com>
> Closes: https://lore.kernel.org/all/8218e149-7718-4432-9312-f97297c352b9@linux.ibm.com
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
> Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>

Looks good to me.

Acked-by: Juri Lelli <juri.lelli@redhat.com>

Thanks!
Juri