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 246EC33E1; Wed, 13 Aug 2025 01:20:28 +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=1755048031; cv=none; b=sG5zFast4O6+Fc/OE63BJ1eHCLBsFZbxBll+ngZo8rP96xEeYTEfYA3acQ695iU9C+bAWG2SZDJaVRUbk5LmlItWYKkv8eYZrBvhbZhtad1r7lhsyALSAhMmArWcAu5AxM30DFEW2K5SrNUrvR+RHQ3T5KqDrKZKFCA/z8ia6d8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755048031; c=relaxed/simple; bh=frm/gAIrsIA/t0ceoa3EtLxy/yObyblKjU5s0j73t8o=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=m8892f7OpTFswkNORcAl5Jx6744IHfhXrdSx9FhoeAluhEKUtQ6QhTxwmgnby7bpqYsPjcMWpILu3lPpUzabmHLrq4i1/ehz+LmCKlY3fj62PbUvHuxJSqj4v4FSE2e6cHs2LcSwbw06TNN4+elFJjdIxJYcZvsjealtcEeytaw= 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 [172.19.163.216]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTPS id 4c1rCc01QRzYQvD5; Wed, 13 Aug 2025 09:20:28 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.128]) by mail.maildlp.com (Postfix) with ESMTP id 9D31E1A0A22; Wed, 13 Aug 2025 09:20:26 +0800 (CST) Received: from [10.67.109.79] (unknown [10.67.109.79]) by APP4 (Coremail) with SMTP id gCh0CgDXnxBY6JtoiW36DQ--.19298S2; Wed, 13 Aug 2025 09:20:26 +0800 (CST) Message-ID: <95c78188-bf8d-4453-b74f-b8a7dc6ae14d@huaweicloud.com> Date: Wed, 13 Aug 2025 09:20:23 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH -next 1/4] cpuset: remove redundant CS_ONLINE flag To: Waiman Long , tj@kernel.org, hannes@cmpxchg.org, mkoutny@suse.com, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, lujialin4@huawei.com, chenridong@huawei.com References: <20250808092515.764820-1-chenridong@huaweicloud.com> <20250808092515.764820-2-chenridong@huaweicloud.com> <775ef75a-b796-4171-b208-df110a73c558@huaweicloud.com> Content-Language: en-US From: Chen Ridong In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-CM-TRANSID:gCh0CgDXnxBY6JtoiW36DQ--.19298S2 X-Coremail-Antispam: 1UD129KBjvJXoW3XFWxArWUKFy5KryUWF1xZrb_yoW7ur15pF 1kCFyUA398Ca4fGa4qq3yjq34xtrnrJ3WUGr1UKa4rAFsFyFya9r40qr909F1UJr48Cryj yF4avrWS9FnrJrJanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUv0b4IE77IF4wAFF20E14v26ryj6rWUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_tr0E3s1l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Gr1j6F4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x 0267AKxVW0oVCq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG 6I80ewAv7VC0I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFV Cjc4AY6r1j6r4UM4x0Y48IcVAKI48JM4IIrI8v6xkF7I0E8cxan2IY04v7MxkF7I0En4kS 14v26r4a6rW5MxAIw28IcxkI7VAKI48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E5I 8CrVAFwI0_Jr0_Jr4lx2IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVW8ZVWr XwCIc40Y0x0EwIxGrwCI42IY6xIIjxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY1x 0267AKxVW8JVWxJwCI42IY6xAIw20EY4v20xvaj40_Jr0_JF4lIxAIcVC2z280aVAFwI0_ Jr0_Gr1lIxAIcVC2z280aVCY1x0267AKxVW8JVW8JrUvcSsGvfC2KfnxnUUI43ZEXa7IU0 s2-5UUUUU== X-CM-SenderInfo: hfkh02xlgr0w46kxt4xhlfz01xgou0bp/ On 2025/8/13 9:00, Waiman Long wrote: > On 8/12/25 8:54 PM, Chen Ridong wrote: >> >> On 2025/8/12 22:44, Waiman Long wrote: >>> On 8/8/25 5:25 AM, Chen Ridong wrote: >>>> From: Chen Ridong >>>> >>>> The CS_ONLINE flag was introduced prior to the CSS_ONLINE flag in the >>>> cpuset subsystem. Currently, the flag setting sequence is as follows: >>>> >>>> 1. cpuset_css_online() sets CS_ONLINE >>>> 2. css->flags gets CSS_ONLINE set >>>> ... >>>> 3. cgroup->kill_css sets CSS_DYING >>>> 4. cpuset_css_offline() clears CS_ONLINE >>>> 5. css->flags clears CSS_ONLINE >>>> >>>> The is_cpuset_online() check currently occurs between steps 1 and 3. >>>> However, it would be equally safe to perform this check between steps 2 >>>> and 3, as CSS_ONLINE provides the same synchronization guarantee as >>>> CS_ONLINE. >>>> >>>> Since CS_ONLINE is redundant with CSS_ONLINE and provides no additional >>>> synchronization benefits, we can safely remove it to simplify the code. >>>> >>>> Signed-off-by: Chen Ridong >>>> --- >>>>    include/linux/cgroup.h          | 5 +++++ >>>>    kernel/cgroup/cpuset-internal.h | 3 +-- >>>>    kernel/cgroup/cpuset.c          | 4 +--- >>>>    3 files changed, 7 insertions(+), 5 deletions(-) >>>> >>>> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h >>>> index b18fb5fcb38e..ae73dbb19165 100644 >>>> --- a/include/linux/cgroup.h >>>> +++ b/include/linux/cgroup.h >>>> @@ -354,6 +354,11 @@ static inline bool css_is_dying(struct cgroup_subsys_state *css) >>>>        return css->flags & CSS_DYING; >>>>    } >>>>    +static inline bool css_is_online(struct cgroup_subsys_state *css) >>>> +{ >>>> +    return css->flags & CSS_ONLINE; >>>> +} >>>> + >>>>    static inline bool css_is_self(struct cgroup_subsys_state *css) >>>>    { >>>>        if (css == &css->cgroup->self) { >>>> diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h >>>> index 383963e28ac6..75b3aef39231 100644 >>>> --- a/kernel/cgroup/cpuset-internal.h >>>> +++ b/kernel/cgroup/cpuset-internal.h >>>> @@ -38,7 +38,6 @@ enum prs_errcode { >>>>      /* bits in struct cpuset flags field */ >>>>    typedef enum { >>>> -    CS_ONLINE, >>>>        CS_CPU_EXCLUSIVE, >>>>        CS_MEM_EXCLUSIVE, >>>>        CS_MEM_HARDWALL, >>>> @@ -202,7 +201,7 @@ static inline struct cpuset *parent_cs(struct cpuset *cs) >>>>    /* convenient tests for these bits */ >>>>    static inline bool is_cpuset_online(struct cpuset *cs) >>>>    { >>>> -    return test_bit(CS_ONLINE, &cs->flags) && !css_is_dying(&cs->css); >>>> +    return css_is_online(&cs->css) && !css_is_dying(&cs->css); >>>>    } >>>>      static inline int is_cpu_exclusive(const struct cpuset *cs) >>>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c >>>> index f74d04429a29..cf7cd2255265 100644 >>>> --- a/kernel/cgroup/cpuset.c >>>> +++ b/kernel/cgroup/cpuset.c >>>> @@ -207,7 +207,7 @@ static inline void notify_partition_change(struct cpuset *cs, int old_prs) >>>>     * parallel, we may leave an offline CPU in cpu_allowed or some other masks. >>>>     */ >>>>    static struct cpuset top_cpuset = { >>>> -    .flags = BIT(CS_ONLINE) | BIT(CS_CPU_EXCLUSIVE) | >>>> +    .flags = BIT(CS_CPU_EXCLUSIVE) | >>>>             BIT(CS_MEM_EXCLUSIVE) | BIT(CS_SCHED_LOAD_BALANCE), >>>>        .partition_root_state = PRS_ROOT, >>>>        .relax_domain_level = -1, >>> top_cpuset.css is not initialized like the one in the children. If you modify is_cpuset_online() to >>> test the css.flags, you will probably need to set the CSS_ONLINE flag in top_cpuset.css.flags. I do >>> doubt that we will apply the is_cpuset_online() test on top_cpuset. To be consistent, we should >>> support that. >>> >>> BTW, other statically allocated css'es in the cgroup root may have similar problem. If you make the >>> css_is_online() helper available to all other controllers, you will have to document that >>> limitation. >>> >>> Cheers, >>> Longman >> Hi, Longman, thank you for your response. >> >> If I understand correctly, the CSS_ONLINE flag should be set in top_cpuset.css during the following >> process: >> >> css_create >>    css = ss->css_alloc(parent_css);  // cgroup root is static, unlike children >>    online_css(css); >>       ret = ss->css_online(css);     // css root may differ from children >>       css->flags |= CSS_ONLINE;      // css.flags is set with CSS_ONLINE, including the root css >> >> I think css online must be successful, and it's CSS_ONLINE flag must be set. Do I missing anything? > > I am talking about just the top_cpuset which is statically allocated. It is not created by the > css_create() call and so the CSS_ONLINE will not be set. > > Cheers, > Longman Hi Longman, Apologies for the call stack earlier. Thank you for your patience in clarifying this matter. The CSS root is brought online through the following initialization flow: cgroup_init_subsys css = ss->css_alloc(NULL); // css root is static, unlike children online_css(css) ret = ss->css_online(css); // css root may differ from children css->flags |= CSS_ONLINE; // css.flags is set with CSS_ONLINE, including the root css My key point is that: - The root CSS should be online by design. - Root css CSS_ONLINE flag should be properly set during initialization. Best regards, Ridong