From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from dggsgout11.his.huawei.com (dggsgout11.his.huawei.com [45.249.212.51]) (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 2658F3C1F; Wed, 26 Nov 2025 01:01:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.51 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764118884; cv=none; b=Ap5TijGnwxbum1cd4rNw2GxOyt1DuaEXtC5yAHGTlnqurTTYM22MYq6OWJPpmx9vl3zt1Ok8M5HKIO8P79h8gBjHrqSNNF6V3uQFBDP3U2cFz+VeEKMeQsPENtZP36AHYtv+PQ0uN1HGjeVL6wf9BFSnp25rlHMwhY+zBWIxPG0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764118884; c=relaxed/simple; bh=Rm2zmhpRt25dnkA7MjYVo3Cd8MqiTTXhaDDf+KLkxCU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=eBIxQHaS/8SDoF2QC5IqX7T/QYrGrIWt++Z9reSQwgsPj13Ncq8qEbXdwxg2VqEfRylIL/jvftm1cRn74adBcL84ocJitDHLE1HP776K2supChOF97+47NcNXDsAoVBl6mLiLWEwabK5ODG0IvTN/tlMzl/0FVYVrjTOnSv3ZB4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com; spf=pass smtp.mailfrom=huaweicloud.com; arc=none smtp.client-ip=45.249.212.51 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huaweicloud.com Received: from mail.maildlp.com (unknown [172.19.93.142]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTPS id 4dGLnx5RzzzYQtnm; Wed, 26 Nov 2025 09:00:21 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.128]) by mail.maildlp.com (Postfix) with ESMTP id D11C71A07BD; Wed, 26 Nov 2025 09:01:12 +0800 (CST) Received: from [10.67.111.176] (unknown [10.67.111.176]) by APP4 (Coremail) with SMTP id gCh0CgBXgF1XUSZpMyMgCA--.25134S2; Wed, 26 Nov 2025 09:01:12 +0800 (CST) Message-ID: <0ecb1476-2886-430f-a698-cabbe9302129@huaweicloud.com> Date: Wed, 26 Nov 2025 09:01:11 +0800 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 -next] cpuset: Remove unnecessary checks in rebuild_sched_domains_locked To: Waiman Long , tj@kernel.org, hannes@cmpxchg.org, mkoutny@suse.com Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, daniel.m.jordan@oracle.com, lujialin4@huawei.com, chenridong@huawei.com References: <20251118083643.1363020-1-chenridong@huaweicloud.com> <27ed2c0b-7b00-4be0-a134-3c370cf85d8e@redhat.com> Content-Language: en-US From: Chen Ridong In-Reply-To: <27ed2c0b-7b00-4be0-a134-3c370cf85d8e@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-CM-TRANSID:gCh0CgBXgF1XUSZpMyMgCA--.25134S2 X-Coremail-Antispam: 1UD129KBjvJXoWxWr48ZF43Kw1xJr4UGr18uFg_yoW7Gr1DpF 1kKrW7XrW5Kr18C3yUJ347Xry8Kw4kJanrJrn8XF18ArW7AF1v9r1jqrn0grWUXrs3Wr1U Ar1UXrnrZF1UAFJanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUylb4IE77IF4wAFF20E14v26r4j6ryUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_tr0E3s1l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Gr1j6F4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x 0267AKxVW0oVCq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG 6I80ewAv7VC0I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFV Cjc4AY6r1j6r4UM4x0Y48IcVAKI48JMxkF7I0En4kS14v26r1q6r43MxAIw28IcxkI7VAK I48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E5I8CrVAFwI0_Jr0_Jr4lx2IqxVCjr7 xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWUtVW8ZwCIc40Y0x0EwIxGrwCI42IY6xII jxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY1x0267AKxVWUJVW8JwCI42IY6xAIw2 0EY4v20xvaj40_Jr0_JF4lIxAIcVC2z280aVAFwI0_Jr0_Gr1lIxAIcVC2z280aVCY1x02 67AKxVWUJVW8JbIYCTnIWIevJa73UjIFyTuYvjxUF1v3UUUUU X-CM-SenderInfo: hfkh02xlgr0w46kxt4xhlfz01xgou0bp/ On 2025/11/26 2:16, Waiman Long wrote: > On 11/18/25 3:36 AM, Chen Ridong wrote: >> From: Chen Ridong >> >> Commit 406100f3da08 ("cpuset: fix race between hotplug work and later CPU >> offline")added a check for empty effective_cpus in partitions for cgroup >> v2. However, thischeck did not account for remote partitions, which were >> introduced later. >> >> After commit 2125c0034c5d ("cgroup/cpuset: Make cpuset hotplug processing >> synchronous"),cgroup v2's cpuset hotplug handling is now synchronous. This >> eliminates the race condition with subsequent CPU offline operations that >> the original check aimed to fix. > That is true. The original asynchronous cpuset_hotplug_workfn() is called after the hotplug > operation finishes. So cpuset can be in a state where cpu_active_mask was updated, but not the > effective cpumasks in cpuset. >> >> Instead of extending the check to support remote partitions, this patch >> removes the redundant partition effective_cpus check. Additionally, it adds >> a check and warningto verify that all generated sched domains consist of > "warningto" => "warning to" Thank you Longman, will update. >> active CPUs, preventing partition_sched_domains from being invoked with >> offline CPUs. >> >> Signed-off-by: Chen Ridong >> --- >>   kernel/cgroup/cpuset.c | 29 ++++++----------------------- >>   1 file changed, 6 insertions(+), 23 deletions(-) >> >> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c >> index daf813386260..1ac58e3f26b4 100644 >> --- a/kernel/cgroup/cpuset.c >> +++ b/kernel/cgroup/cpuset.c >> @@ -1084,11 +1084,10 @@ void dl_rebuild_rd_accounting(void) >>    */ >>   void rebuild_sched_domains_locked(void) >>   { >> -    struct cgroup_subsys_state *pos_css; >>       struct sched_domain_attr *attr; >>       cpumask_var_t *doms; >> -    struct cpuset *cs; >>       int ndoms; >> +    int i; >>         lockdep_assert_cpus_held(); >>       lockdep_assert_held(&cpuset_mutex); > > In fact, the following code and the comments above in rebuild_sched_domains_locked() are also no > longer relevant. So you may remove them as well. > >         if (!top_cpuset.nr_subparts_cpus && >             !cpumask_equal(top_cpuset.effective_cpus, cpu_active_mask)) >                 return; > Thank you for reminding me. I initially retained this code because I believed it was still required for cgroup v1, as I recalled that synchronous operation is exclusive to cgroup v2. However, upon re-examining the code, I confirm it can be safely removed. For cgroup v1, rebuild_sched_domains_locked is called synchronously, and only the migration task (handled by cpuset_migrate_tasks_workfn) operates asynchronously. Consequently, cpuset_hotplug_workfn is guaranteed to complete before the hotplug workflow finishes. >> @@ -1107,30 +1106,14 @@ void rebuild_sched_domains_locked(void) >>           !cpumask_equal(top_cpuset.effective_cpus, cpu_active_mask)) >>           return; >>   -    /* >> -     * With subpartition CPUs, however, the effective CPUs of a partition >> -     * root should be only a subset of the active CPUs.  Since a CPU in any >> -     * partition root could be offlined, all must be checked. >> -     */ >> -    if (!cpumask_empty(subpartitions_cpus)) { >> -        rcu_read_lock(); >> -        cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) { >> -            if (!is_partition_valid(cs)) { >> -                pos_css = css_rightmost_descendant(pos_css); >> -                continue; >> -            } >> -            if (!cpumask_subset(cs->effective_cpus, >> -                        cpu_active_mask)) { >> -                rcu_read_unlock(); >> -                return; >> -            } >> -        } >> -        rcu_read_unlock(); >> -    } >> - >>       /* Generate domain masks and attrs */ >>       ndoms = generate_sched_domains(&doms, &attr); >>   +    for (i = 0; i < ndoms; ++i) { >> +        if (WARN_ON_ONCE(!cpumask_subset(doms[i], cpu_active_mask))) >> +            return; >> +    } >> + > > If it is not clear about the purpose of the WARN_ON_ONCE() call, we should add a comment to explain > that cpu_active_mask will not be out of sync with cpuset's effective cpumasks. So the warning should > not be triggered. > Will add. > Cheers, > Longman > >>       /* Have scheduler rebuild the domains */ >>       partition_sched_domains(ndoms, doms, attr); >>   } > -- Best regards, Ridong