From nobody Sun Feb 8 09:27:02 2026 Received: from canpmsgout02.his.huawei.com (canpmsgout02.his.huawei.com [113.46.200.217]) (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 17EE030C615 for ; Thu, 22 Jan 2026 01:45:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=113.46.200.217 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769046346; cv=none; b=nU6RAufBHTKuKITnSPyis2jhoNo3W+wa3rtktSscLN+BrcmC3/xIQONSqUJrk/1IRzxDsaCz4+5wWgra3e208K303dOcLF5+EecP2OHRqdqmx6SUycA41TCvOdDyAd/3T7jjlV5N15/HnE4VU0GvIUJ7w1zwY/7u2iNm3N4xcvs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769046346; c=relaxed/simple; bh=iWDzowDeu+DpIjkNTpwj1UqeUa57xKFKZrVvj1AcQEw=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=DrrChfXlplBc/OS/s6jGHJ9FjMBf4mivnVQXDIraF3fXxntZXdp4DrthGq547U/SExNSaEbT+pr3hXypip1WmHZ/upmuv3NxYJAVf9SLxecSIatR+wlZsTTLq61GprfI6dor6CpJPg6p/gvg6DwMyvpi9kH/oA+1P5BieyPU7qw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b=ZaDa2gxy; arc=none smtp.client-ip=113.46.200.217 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 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b="ZaDa2gxy" dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=AeyiKQMUkY34WIu9zoqHHhLYA/WvBVVNvQdeGmPSpLE=; b=ZaDa2gxyKOdVxdmSsaWDQXcP+ZaicC+N/2rzyYQc0tilCZXVbJNvxpPAadSPu6vEbS+dhdjyD B6sCug/jFK1HCP99vxOSsefoTXeHlTTJD4tfU2F0h/b7EbQDHG5sdE/oGd+OcWiTTW83fDbcd46 JPy9iNPQUBQfKghJRoHcDD0= Received: from mail.maildlp.com (unknown [172.19.163.0]) by canpmsgout02.his.huawei.com (SkyGuard) with ESMTPS id 4dxP1D0pk0zcZxy; Thu, 22 Jan 2026 09:41:36 +0800 (CST) Received: from kwepemg100008.china.huawei.com (unknown [7.202.181.26]) by mail.maildlp.com (Postfix) with ESMTPS id 8CDE94056B; Thu, 22 Jan 2026 09:45:34 +0800 (CST) Received: from huawei.com (10.67.174.242) by kwepemg100008.china.huawei.com (7.202.181.26) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.36; Thu, 22 Jan 2026 09:45:33 +0800 From: Chen Jinghuang To: , , , CC: , , , , , Subject: [RESEND] sched/rt: Skip currently executing CPU in rto_next_cpu() Date: Thu, 22 Jan 2026 01:25:33 +0000 Message-ID: <20260122012533.673768-1-chenjinghuang2@huawei.com> X-Mailer: git-send-email 2.34.1 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: kwepems500002.china.huawei.com (7.221.188.17) To kwepemg100008.china.huawei.com (7.202.181.26) Content-Type: text/plain; charset="utf-8" CPU0 becomes overloaded when hosting a CPU-bound RT task, a non-CPU-bound RT task, and a CFS task stuck in kernel space. When other CPUs switch from RT to non-RT tasks, RT load balancing (LB) is triggered; with HAVE_RT_PUSH_IPI enabled, they send IPIs to CPU0 to drive the execution of rto_push_irq_work_func. During push_rt_task on CPU0, if next_task->prio < rq->donor->prio, resched_curr() sets NEED_RESCHED and after the push operation completes, CPU0 calls rto_next_cpu(). Since only CPU0 is overloaded in this scenario, rto_next_cpu() should ideally return -1 (no further IPI needed). However, multiple CPUs invoking tell_cpu_to_push() during LB increments rd->rto_loop_next. Even when rd->rto_cpu is set to -1, the mismatch between rd->rto_loop and rd->rto_loop_next forces rto_next_cpu() to restart its search from -1. With CPU0 remaining overloaded (satisfying rt_nr_migratory && rt_nr_total > 1), it gets reselected, causing CPU0 to queue irq_work to itself and send self-IPIs repeatedly. As long as CPU0 stays overloaded and other CPUs run pull_rt_tasks(), it falls into an infinite self-IPI loop, which triggers a CPU hardlockup due to continuous self-interrupts. The trigging scenario is as follows: cpu0 cpu1 cpu2 pull_rt_task tell_cpu_to_push <------------irq_work_queue_on rto_push_irq_work_func push_rt_task resched_curr(rq) pull_rt_task rto_next_cpu tell_cpu_to_push <-------------------------- atomic_inc(rto_loop_next) rd->rto_loop !=3D next rto_next_cpu irq_work_queue_on rto_push_irq_work_func Fix redundant self-IPI by filtering the initiating CPU in rto_next_cpu(). This solution has been verified to effectively eliminate spurious self-IPIs and prevent CPU hardlockup scenarios. Fixes: 4bdced5c9a29 ("sched/rt: Simplify the IPI based RT balancing logic") Suggested-by: Steven Rostedt (Google) Suggested-by: K Prateek Nayak Signed-off-by: Chen Jinghuang Reviewed-by: Steven Rostedt (Google) Reviewed-by: Valentin Schneider --- Changes since v4: https://lore.kernel.org/all/20260108070355.259530-1-chenj= inghuang2@huawei.com/ - Add Reviewed-by tag from Valentin Schneider Changes since v3: https://lore.kernel.org/all/20260105034012.3196947-1-chen= jinghuang2@huawei.com/ - Replace the do-while loop with a continue statement to simplify the loop = logic - Add Suggested-by tag from K Prateek Nayak Changes since v2: https://lore.kernel.org/all/20251125083649.1814558-1-chen= jinghuang2@huawei.com/ - Replace the original "check NEED_RESCHED on target CPU" logic with "skip the currently executing CPU" - This modification eliminates self-IPIS Changes since v1: https://lore.kernel.org/all/20251121014004.564508-1-chenj= inghuang2@huawei.com/ - Remove unneeded extra whitespace - Add Reviewed-by tag from Steven Rostedt --- kernel/sched/rt.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index f1867fe8e5c5..e0ff90905019 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -2100,6 +2100,7 @@ static void push_rt_tasks(struct rq *rq) */ static int rto_next_cpu(struct root_domain *rd) { + int this_cpu =3D smp_processor_id(); int next; int cpu; =20 @@ -2123,6 +2124,10 @@ static int rto_next_cpu(struct root_domain *rd) =20 rd->rto_cpu =3D cpu; =20 + /* Do not send IPI to self */ + if (cpu =3D=3D this_cpu) + continue; + if (cpu < nr_cpu_ids) return cpu; =20 --=20 2.34.1