On 09.10.2025 20:47, Shrikanth Hegde wrote: > From: Peter Zijlstra (Intel) <[email protected]> > > 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 protected]/ > [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 protected]> > Closes: > https://lore.kernel.org/all/[email protected] Closes: https://lore.kernel.org/all/[email protected]/ > Signed-off-by: Peter Zijlstra (Intel) <[email protected]> > Signed-off-by: Shrikanth Hegde <[email protected]> > Tested-by: Marek Szyprowski <[email protected]> > Tested-by: Shrikanth Hegde <[email protected]> > --- > 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))
Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
