Re: [PATCH] sched/deadline: stop dl_server before CPU goes offline
From: Venkat <hidden>
Date: 2025-10-10 05:00:08
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On 10 Oct 2025, at 12:17 AM, Shrikanth Hegde [off-list ref] 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/ (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>This patch fixes reported issue. Please add below tag. Tested-by: Venkat Rao Bagalkote <redacted> Regards, Venkat.
quoted hunk ↗ jump to hunk
--- kernel/sched/core.c | 2 ++ kernel/sched/deadline.c | 3 +++ 2 files changed, 5 insertions(+)diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 198d2dd45f59..f1ebf67b48e2 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c@@ -8571,10 +8571,12 @@ int sched_cpu_dying(unsigned int cpu)sched_tick_stop(cpu); rq_lock_irqsave(rq, &rf); + update_rq_clock(rq); if (rq->nr_running != 1 || rq_has_pinned_tasks(rq)) { WARN(true, "Dying CPU not properly vacated!"); dump_rq_tasks(rq, KERN_WARNING); } + dl_server_stop(&rq->fair_server); rq_unlock_irqrestore(rq, &rf); calc_load_migrate(rq);diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 615411a0a881..7b7671060bf9 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c@@ -1582,6 +1582,9 @@ void dl_server_start(struct sched_dl_entity *dl_se)if (!dl_server(dl_se) || dl_se->dl_server_active) return; + if (WARN_ON_ONCE(!cpu_online(cpu_of(rq)))) + return; + dl_se->dl_server_active = 1; enqueue_dl_entity(dl_se, ENQUEUE_WAKEUP); if (!dl_task(dl_se->rq->curr) || dl_entity_preempt(dl_se, &rq->curr->dl)) -- 2.47.3