From nobody Wed Jan 7 22:50:47 2026 Received: from canpmsgout01.his.huawei.com (canpmsgout01.his.huawei.com [113.46.200.216]) (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 B004C320A37 for ; Mon, 5 Jan 2026 03:59:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=113.46.200.216 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767585590; cv=none; b=K5L3LBy3MeYR6cnLZgOaZM9lLlBipRVB0UdwoP1eDAU5RpSGRw4iVqN4AoYNYca4Fw+26k8EPftcb6Z+6b1cWMxIXv9A5hoOIHKyTuLvHAFN4gYyiB6NRT/RWBvKcje84qRy2qdyQalxX++0CwKxjSis5YnfYnUYatLn8+ptTfI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767585590; c=relaxed/simple; bh=TQ1aNctk5zDmjxkV8b2Di/qDtIp8po53a2m0tZUP+6E=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=NSrUQHQ0HAr0xRGIxsIppVQwGdyYrelqGZNNIgn9f7GSpNYuPoYwQJA1QSog+VrsT7IkMzyoQkUV786qYX5d5gRjdxSTqgc2llQCAQKFiEWidaWV0z7/RErbWfpgRsLsUUyMsZLxDQn6dYw5bpkI12JjtvsWt86sbIT/QvnYF5g= 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=baonN3+O; arc=none smtp.client-ip=113.46.200.216 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="baonN3+O" dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=lnZu+MDAPSt967roHZs8nzBE+bYi53SFWojhFRyTVBg=; b=baonN3+OEY/yIgDx+WVUK18yAg56GBRGK+1AL9kTKXxC9zjuFcPNCtJSKSfIz1vt0H4xo9AOF p9AYjWBr1ZAr3Y+wAo1C38BTIW7EiImYBXJmlE3evy4+zxnnHyn9/EGr1aCLYJw4JKcOCm0ArVl 7yCUU9ISB6ApiuV7tLJGrbA= Received: from mail.maildlp.com (unknown [172.19.162.140]) by canpmsgout01.his.huawei.com (SkyGuard) with ESMTPS id 4dl0qQ3tTbz1T4GS; Mon, 5 Jan 2026 11:57:06 +0800 (CST) Received: from kwepemg100008.china.huawei.com (unknown [7.202.181.26]) by mail.maildlp.com (Postfix) with ESMTPS id 128412016A; Mon, 5 Jan 2026 11:59:45 +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; Mon, 5 Jan 2026 11:59:44 +0800 From: Chen Jinghuang To: , , , CC: , , , , , Subject: [RESEND] sched/rt: Skip currently executing CPU in rto_next_cpu() Date: Mon, 5 Jan 2026 03:40:12 +0000 Message-ID: <20260105034012.3196947-1-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: kwepems100002.china.huawei.com (7.221.188.206) 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) Signed-off-by: Chen Jinghuang Reviewed-by: Steven Rostedt (Google) --- 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 | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index f1867fe8e5c5..ec10ed7bb75d 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 @@ -2118,10 +2119,13 @@ static int rto_next_cpu(struct root_domain *rd) */ for (;;) { =20 - /* When rto_cpu is -1 this acts like cpumask_first() */ - cpu =3D cpumask_next(rd->rto_cpu, rd->rto_mask); + do { + /* When rto_cpu is -1 this acts like cpumask_first() */ + cpu =3D cpumask_next(rd->rto_cpu, rd->rto_mask); =20 - rd->rto_cpu =3D cpu; + rd->rto_cpu =3D cpu; + /* Do not send IPI to self */ + } while (cpu =3D=3D this_cpu); =20 if (cpu < nr_cpu_ids) return cpu; --=20 2.34.1