From nobody Fri Dec 19 08:09:47 2025 Received: from szxga04-in.huawei.com (szxga04-in.huawei.com [45.249.212.190]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1D8AD125A8 for ; Tue, 19 Dec 2023 08:29:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.88.214]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4SvVGY3VX9z1wp0D; Tue, 19 Dec 2023 16:29:09 +0800 (CST) Received: from dggpeml500003.china.huawei.com (unknown [7.185.36.200]) by mail.maildlp.com (Postfix) with ESMTPS id EA9301A0192; Tue, 19 Dec 2023 16:29:22 +0800 (CST) Received: from huawei.com (10.44.142.84) by dggpeml500003.china.huawei.com (7.185.36.200) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.35; Tue, 19 Dec 2023 16:29:22 +0800 From: Yu Liao To: , CC: , , , , Subject: [PATCH] tick/broadcast-hrtimer: Prevent the timer device on broadcast duty CPU from being disabled Date: Mon, 18 Dec 2023 10:58:44 +0800 Message-ID: <20231218025844.55675-1-liaoyu15@huawei.com> X-Mailer: git-send-email 2.33.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To dggpeml500003.china.huawei.com (7.185.36.200) Content-Type: text/plain; charset="utf-8" It was found that running the LTP hotplug stress test on a aarch64 system could produce rcu_sched stall warnings. The issue is the following: CPU1 (owns the broadcast hrtimer) CPU2 tick_broadcast_enter() //shut down local timer device ... tick_broadcast_exit() //exits with tick_broadcast_force_mask set, timer device remains disabled initiates offlining of CPU1 take_cpu_down() //CPU1 shuts down and does not send broadcast IPI anymore takedown_cpu() hotplug_cpu__broadcast_tick_pull() //move broadcast hrtimer to this CPU clockevents_program_event() bc_set_next() hrtimer_start() //does not call hrtimer_reprogram() to program timer device if expires equals dev->next_event, so the timer device remains disabled. CPU2 takes over the broadcast duty but local timer device is disabled, causing many CPUs to become stuck. Fix this by calling tick_program_event() to reprogram the local timer device in this scenario. Signed-off-by: Yu Liao --- kernel/time/tick-broadcast-hrtimer.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/kernel/time/tick-broadcast-hrtimer.c b/kernel/time/tick-broadc= ast-hrtimer.c index e28f9210f8a1..6a4a612581fb 100644 --- a/kernel/time/tick-broadcast-hrtimer.c +++ b/kernel/time/tick-broadcast-hrtimer.c @@ -42,10 +42,22 @@ static int bc_shutdown(struct clock_event_device *evt) */ static int bc_set_next(ktime_t expires, struct clock_event_device *bc) { + ktime_t next_event =3D this_cpu_ptr(&tick_cpu_device)->evtdev->next_event; + /* - * This is called either from enter/exit idle code or from the - * broadcast handler. In all cases tick_broadcast_lock is held. - * + * This can be called from CPU offline operation to move broadcast + * assignment. If tick_broadcast_force_mask is set, the CPU local + * timer device may be disabled. And hrtimer_reprogram() will not + * called if the timer is not the first expiring timer. Reprogram + * the cpu local timer device to ensure we can take over the + * broadcast duty. + */ + if (tick_check_broadcast_expired() && expires >=3D next_event) + tick_program_event(next_event, 1); + + /* + * This is called from enter/exit idle code, broadcast handler or + * CPU offline operation. In all cases tick_broadcast_lock is held. * hrtimer_cancel() cannot be called here neither from the * broadcast handler nor from the enter/exit idle code. The idle * code can run into the problem described in bc_shutdown() and the --=20 2.33.0