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Sun, 8 Nov 2026 19:06:43 +0000 (UTC) Received: from [100.91.18.181] (headnet04.pony-001.prod.iad2.dc.redhat.com [10.2.32.116]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id B73F63001DA5; Sun, 8 Nov 2026 19:06:41 +0000 (UTC) Message-ID: Date: Sun, 8 Nov 2026 14:06:40 -0500 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [BUG] cpuset: empty sched domain with isolcpus=domain, panic at CPU offline To: Mathieu Desnoyers Cc: Chen Yu , Peter Zijlstra , Guopeng Zhang , Tejun Heo , Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Ridong Chen , Tim Chen , Valentin Schneider , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org References: <20261108145744.1532128-1-mathieu.desnoyers@efficios.com> <12cb0bee-57aa-4609-bc2e-77806e0b6805@redhat.com> <20261108184620.1548615-1-mathieu.desnoyers@efficios.com> Content-Language: en-US From: Waiman Long In-Reply-To: <20261108184620.1548615-1-mathieu.desnoyers@efficios.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 On 11/8/26 1:46 PM, Mathieu Desnoyers wrote: > On 2026-11-08 13:35, Waiman Long wrote: > [...] >> Yes, we are going to add the check to make sure that there will be at >> least one housekeeping CPU left for the top_cpuset sched domain. >> >> See >> https://lore.kernel.org/lkml/20261105130344.664336-1-guopeng.zhang@linux.dev/ > Thanks, I had missed that series. Refusing such a partition is a better > fix than giving the top cpuset no sched domain. > >> This patch is correct AFAICS. I am not against it but it may not be >> necessary after we make sure that there is at least one HK online CPU in >> the top sched domain. > Then I will drop my patch and rely on Guopeng's series. I can test its > v3 on the setup that hit the panic: 5 vCPUs with isolcpus=domain,0,1. > > By my reading, your _cpu_down() patch covers a case that cpuset cannot > fix. With no partition, the last online housekeeping CPU could go > offline. No partition could then give one back. Yes, that is the point. Cheers, Longman