From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 DC5377261D for ; Tue, 15 Jul 2025 16:00:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752595252; cv=none; b=GuEAbeyiND3bFQL42myK3DWM22kBj7qoZjXmyH8DNSUyf0MHVpX4e38Et8R/JORtIIw+gcW3E0GIiWhZW8Ml5fWwTtopGHVPiUlIq4E181ffZ3tZYOCoea1pxGUNBdX6Bm6aPZlTgX66f6MOUwiCnoCLIBWS47FJ2a/4/AQLsDY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752595252; c=relaxed/simple; bh=QGDL0kvdCWFlRnKscgJjq+k+L0QvyBPNvfMVFZrVcWo=; h=From:Message-ID:Date:MIME-Version:Subject:To:Cc:References: In-Reply-To:Content-Type; b=lQQKIqPcpjJ+KNP+zBsiUtotdKtcclCpffO1tBWODppmSDgTolj/CN0qDjBnfRnIH1RnxEiHlrmWGdirtVzE12z57h41NAS1GsfPggUwcj6jT2mhig36lH4/FCZ5/XynRNXpF+ftxiu/WaK9Vjq4RaUXCqbfeH72d98caPRYV9U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=VW6aBWGB; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="VW6aBWGB" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1752595249; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=TXwosRAk7cpmUzQUy+WVJ4W1gQSc+hb1c+UjkCUp6Uk=; b=VW6aBWGBQVMiFNXHP6ciyoAVrFbwZ+wcLfDhsvJWkkXXg/RGZG/7aJ5WllrI7LSRelWJQk pRMa7DkYPo3Imk2gyCYtns+ZrM1TG6Mp4+XJckWVCqrENGfLqCwIHnJ/xCeCUMJoN9eLtc Qd3iM4WQH4bRfG6M+5auS106rqVyass= Received: from mail-qk1-f199.google.com (mail-qk1-f199.google.com [209.85.222.199]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-654-Hmy0AKg1Py2_X-KFTbKAUw-1; Tue, 15 Jul 2025 12:00:48 -0400 X-MC-Unique: Hmy0AKg1Py2_X-KFTbKAUw-1 X-Mimecast-MFC-AGG-ID: Hmy0AKg1Py2_X-KFTbKAUw_1752595248 Received: by mail-qk1-f199.google.com with SMTP id af79cd13be357-7da0850c9e5so923999985a.0 for ; Tue, 15 Jul 2025 09:00:48 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1752595248; x=1753200048; h=content-transfer-encoding:in-reply-to:content-language:references :cc:to:subject:user-agent:mime-version:date:message-id:from :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=TXwosRAk7cpmUzQUy+WVJ4W1gQSc+hb1c+UjkCUp6Uk=; b=ml3S2wuWD42FySa6yO9JSdCdHHNRCmrU+G4OEVQ5SJcv86jjrfx3tVw0AuVJcw+SJU JT4HeH26XYZcZ5RFOYyh/AiMOpms5m1lNGalbIvkDIRxlyRIedpDCM2GOmENE4pnMreE eelGkNl9eJX44AZzYxpvVUOv0gUmHJtU9Rn46DBJEdhvw48veetSDecrAVS95kVLsWG2 rN3zEnXyxAYzNQoFbaziqrXyHCk04MRBrsQYWY4h1D7U8mlTbgauV/7l47F3l2EBLaWZ t0KYgTZL1PpEKFBJilG3p0freZmr0X/Z5QrZ9mg+ixqw4/pQ4AG3zjAeF63dXgtxv39Q 2sZQ== X-Gm-Message-State: AOJu0YxAkpTSIwCeiq32T1LK69W6M1xKyeQt3cd1T4ck5GO5BjZcE2b6 1UymAdKzHH2UpGEwU5o2r64fGFbdr8XBFGnaV/IgZzOIzQFAS1YE0tAsDj0eWlmbVhXfJqO80uW HZb2NwaCQMC9OmR3XlNTnyfiMONVZyBfKOy6FL+AhS0Fs2QeysuVaPBbHnuA= X-Gm-Gg: ASbGncuobmrckzijRMFE63y5QaFzr77zvdn0gIZI2DvTqQbQZkL6qI2Slw/5E3IG+1t d6lSpe9edxwYPpt1ES3gBuhjQIDMTeZDd1Q6GTaV3Dq9yBSgnN1fpTSm+jlAqkafrXr8QsNZvtb +BdygDLUrxwMd/YXb4kMonsvoEyl57dCLzczobt/L+sdR9LnwDVBIHplJ4iXoHkei20DMZ0NE6w HpEkhK6kcvAuOciFAMkWqSUaiKG2Kohn+6vmPWLyp2wMctCrbE66uHrHiw7vvVbyZwax70IVCDp KbJwpRqI3/TVKnm/+o7ZcspM0/jvfTRejH4g5qD5Gd3c6Sado66fjssu1kk7n5o+vcXeyeVvQN1 UfoDvH1hC4Q== X-Received: by 2002:a05:620a:4592:b0:7e0:2c05:6b98 with SMTP id af79cd13be357-7e338be52fbmr423929285a.20.1752595247513; Tue, 15 Jul 2025 09:00:47 -0700 (PDT) X-Google-Smtp-Source: AGHT+IE8OqdBxsggnkLBvim314ncx0zbBASpaeaktiw40LuYsgyHA1nGTYgcxijPhPza/ECjub3h5Q== X-Received: by 2002:a05:620a:4592:b0:7e0:2c05:6b98 with SMTP id af79cd13be357-7e338be52fbmr423920985a.20.1752595246781; Tue, 15 Jul 2025 09:00:46 -0700 (PDT) Received: from ?IPV6:2601:188:c180:4250:ecbe:130d:668d:951d? ([2601:188:c180:4250:ecbe:130d:668d:951d]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7e3081e036esm240838585a.107.2025.07.15.09.00.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 15 Jul 2025 09:00:45 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: Date: Tue, 15 Jul 2025 12:00:43 -0400 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 -next] cpuset: fix warning when attaching tasks with offline CPUs To: Chen Ridong , tj@kernel.org, hannes@cmpxchg.org, mkoutny@suse.com, peterz@infradead.org Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, lujialin4@huawei.com, chenridong@huawei.com References: <20250715023340.3617147-1-chenridong@huaweicloud.com> Content-Language: en-US In-Reply-To: <20250715023340.3617147-1-chenridong@huaweicloud.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 7/14/25 10:33 PM, Chen Ridong wrote: > From: Chen Ridong > > A kernel warning was observed in the cpuset migration path: > > WARNING: CPU: 3 PID: 123 at kernel/cgroup/cpuset.c:3130 > cgroup_migrate_execute+0x8df/0xf30 > Call Trace: > cgroup_transfer_tasks+0x2f3/0x3b0 > cpuset_migrate_tasks_workfn+0x146/0x3b0 > process_one_work+0x5ba/0xda0 > worker_thread+0x788/0x1220 > > The issue can be reliably reproduced with: > > # Setup test cpuset > mkdir /sys/fs/cgroup/cpuset/test > echo 2-3 > /sys/fs/cgroup/cpuset/test/cpuset.cpus > echo 0 > /sys/fs/cgroup/cpuset/test/cpuset.mems > > # Start test process > sleep 100 & > pid=$! > echo $pid > /sys/fs/cgroup/cpuset/test/cgroup.procs > taskset -p 0xC $pid # Bind to CPUs 2-3 > > # Take CPUs offline > echo 0 > /sys/devices/system/cpu/cpu3/online > echo 0 > /sys/devices/system/cpu/cpu2/online > > Root cause analysis: > When tasks are migrated to top_cpuset due to CPUs going offline, > cpuset_attach_task() sets the CPU affinity using cpus_attach which > is initialized from cpu_possible_mask. This mask may include offline > CPUs. When __set_cpus_allowed_ptr() computes the intersection between: > 1. cpus_attach (possible CPUs, may include offline) > 2. p->user_cpus_ptr (original user-set mask) > The resulting new_mask may contain only offline CPUs, causing the > operation to fail. > > To resolve this issue, if the call to set_cpus_allowed_ptr fails, retry > using the intersection of cpus_attach and cpu_active_mask. > > Fixes: da019032819a ("sched: Enforce user requested affinity") > Suggested-by: Waiman Long > Reported-by: Yang Lijin > Signed-off-by: Chen Ridong > --- > kernel/cgroup/cpuset.c | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) Thanking further about this problem, the cpuset patch that I proposed is just a bandage. It is better to fix the problem at its origin in kernel/sched/core.c. I have posted a new patch to do that. Cheers, Longman > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index f74d04429a29..2cf788a8982a 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -3114,6 +3114,10 @@ static void cpuset_cancel_attach(struct cgroup_taskset *tset) > static cpumask_var_t cpus_attach; > static nodemask_t cpuset_attach_nodemask_to; > > +/* > + * Note that tasks in the top cpuset won't get update to their cpumasks when > + * a hotplug event happens. So we include offline CPUs as well. > + */ > static void cpuset_attach_task(struct cpuset *cs, struct task_struct *task) > { > lockdep_assert_held(&cpuset_mutex); > @@ -3127,7 +3131,16 @@ static void cpuset_attach_task(struct cpuset *cs, struct task_struct *task) > * can_attach beforehand should guarantee that this doesn't > * fail. TODO: have a better way to handle failure here > */ > - WARN_ON_ONCE(set_cpus_allowed_ptr(task, cpus_attach)); > + if (unlikely(set_cpus_allowed_ptr(task, cpus_attach))) { > + /* > + * Since offline CPUs are included for top_cpuset, > + * set_cpus_allowed_ptr() can fail if user_cpus_ptr contains > + * only offline CPUs. Take out the offline CPUs and retry. > + */ > + if (cs == &top_cpuset) > + cpumask_and(cpus_attach, cpus_attach, cpu_active_mask); > + WARN_ON_ONCE(set_cpus_allowed_ptr(task, cpus_attach)); > + } > > cpuset_change_task_nodemask(task, &cpuset_attach_nodemask_to); > cpuset1_update_task_spread_flags(cs, task);