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d=samsung.com; s=mail20170921; t=1760041714; bh=PEQt2CgrK+lTlqZJv4b9gffvbDj0I0LwSr+EGVx7o+M=; h=Date:Subject:To:Cc:From:In-Reply-To:References:From; b=nlk+4kPQaPH0OjKtHU2HerZ8oqVXQX4STzkU4FDKBWC0gUTfdoPuTHMZfbgtYCibG 03yoUe2MA2Qxuh6NkMpF8kRek6DVa/wnlrP/KZ1iNNWcYsT8pS53vLrJn2LugbRm22 UGSZ2fwrvO806Tjez4WYllNy7CsGXCm6jmB07FaM= Received: from eusmtip2.samsung.com (unknown [203.254.199.222]) by eucas1p1.samsung.com (KnoxPortal) with ESMTPA id 20251009202834eucas1p1bfe2bd8fdb6360bc836fa09dd2208a58~s7J0yGgka2691726917eucas1p1y; Thu, 9 Oct 2025 20:28:34 +0000 (GMT) Received: from [106.210.134.192] (unknown [106.210.134.192]) by eusmtip2.samsung.com (KnoxPortal) with ESMTPA id 20251009202833eusmtip29563cfd0864227c6682b23fe26571a5b~s7Jz4niFS2491624916eusmtip2D; Thu, 9 Oct 2025 20:28:33 +0000 (GMT) Message-ID: <58f317d8-3137-4847-9a27-cbdf0f54eff2@samsung.com> Date: Thu, 9 Oct 2025 22:28:32 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Betterbird (Windows) Subject: Re: [PATCH] sched/deadline: stop dl_server before CPU goes offline To: Shrikanth Hegde , peterz@infradead.org, juri.lelli@redhat.com Cc: mingo@redhat.com, vincent.guittot@linaro.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, venkat88@linux.ibm.com, jstultz@google.com Content-Language: en-US From: Marek Szyprowski In-Reply-To: <20251009184727.673081-1-sshegde@linux.ibm.com> Content-Transfer-Encoding: 7bit X-CMS-MailID: 20251009202834eucas1p1bfe2bd8fdb6360bc836fa09dd2208a58 X-Msg-Generator: CA Content-Type: text/plain; charset="utf-8" X-RootMTR: 20251009202834eucas1p1bfe2bd8fdb6360bc836fa09dd2208a58 X-EPHeader: CA X-CMS-RootMailID: 20251009202834eucas1p1bfe2bd8fdb6360bc836fa09dd2208a58 References: <20251009184727.673081-1-sshegde@linux.ibm.com> On 09.10.2025 20:47, Shrikanth Hegde wrote: > From: Peter Zijlstra (Intel) > > 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 > Closes: https://lore.kernel.org/all/8218e149-7718-4432-9312-f97297c352b9@linux.ibm.com Closes: https://lore.kernel.org/all/e56310b5-f7a9-4fad-b79a-dcbcdd3d3883@samsung.com/ > Signed-off-by: Peter Zijlstra (Intel) > Signed-off-by: Shrikanth Hegde > Tested-by: Marek Szyprowski > Tested-by: Shrikanth Hegde > --- > 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