From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 BB4AC1D5ABA; Wed, 25 Feb 2026 01:29:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771982949; cv=none; b=BOz6OzMATASCwukKIplWTFlA8kr6V1Tm1ccWAOuvBRZr8SDJWwSDosPpxR5lzdrT38DUDLR7OUxTyzjTcGOAmomCjnHwqIjXCBHFcR5mYb5An6s0TxTS3eTgb/Kwc8TMvZzG1IXneDW4typVXC4sDELh/ouBqzAaBacQUu8P/ps= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771982949; c=relaxed/simple; bh=QbpVWe1Z7A42FwHLHJ6y2xMB5y9RJ3597Wf/LUBrz/Y=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=lWNdrLOS2nsjiKM/ybVhhkWffsg53fU4NRIkMp75iYPr7Z9etGDLHsVgrC+WBOXhR51yVdVh/2aJgbkuFS4JeKnUqt4zyHJOFa8Ilw5rRv2MWFmn18ALnIFANXpldBuOYYnpLzHaiYG6wtmfBVtUflKuqjA+m9QF50rz4A8STTA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=bIVdPUeT; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="bIVdPUeT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 78857C116D0; Wed, 25 Feb 2026 01:29:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1771982949; bh=QbpVWe1Z7A42FwHLHJ6y2xMB5y9RJ3597Wf/LUBrz/Y=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bIVdPUeTXgaSdBVgrxTVPwx1becm96exFpgPrduHXFGxUwUai/rV9i4gEYBlDdpLa 0BkN9V6aEtA0rXbb1uTG16bNhwlBL0Lsetpb4PoJwKPg4E86m+bN4ppiQpKefXcfvj JUKDCKL3pMfU/LW1dswgtOCJ4GizwqqK6e1UmNy0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Steven Rostedt (Google)" , K Prateek Nayak , Chen Jinghuang , "Peter Zijlstra (Intel)" , Valentin Schneider , Sasha Levin Subject: [PATCH 6.19 128/781] sched/rt: Skip currently executing CPU in rto_next_cpu() Date: Tue, 24 Feb 2026 17:13:57 -0800 Message-ID: <20260225012402.812039628@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260225012359.695468795@linuxfoundation.org> References: <20260225012359.695468795@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.19-stable review patch. If anyone has any objections, please let me know. ------------------ From: Chen Jinghuang [ Upstream commit 94894c9c477e53bcea052e075c53f89df3d2a33e ] 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 != 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 Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Steven Rostedt (Google) Reviewed-by: Valentin Schneider Link: https://patch.msgid.link/20260122012533.673768-1-chenjinghuang2@huawei.com Signed-off-by: Sasha Levin --- kernel/sched/rt.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index f1867fe8e5c53..e0ff909050190 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 = smp_processor_id(); int next; int cpu; @@ -2123,6 +2124,10 @@ static int rto_next_cpu(struct root_domain *rd) rd->rto_cpu = cpu; + /* Do not send IPI to self */ + if (cpu == this_cpu) + continue; + if (cpu < nr_cpu_ids) return cpu; -- 2.51.0