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 461EA1DF246; Fri, 4 Jul 2025 03:11:55 +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=1751598720; cv=none; b=bi0YPkYKCCWazbcYo+QMdSDYia3Z2kN8eQRLLl2x6qZQ37IUxgLCNrWVKUzRF6B4Ld5KP+uvgeL0SjT1gRFjTq6O918H3lU4zX/7uAgTCBDlHzZfiPHFpQZjQ6LFg15bZHVofbzQFogI5X+73XYYd0wrD/xGr63SYbxRppFfEPI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751598720; c=relaxed/simple; bh=xpFzJK7EbTj8oT8gx1B/pIapBvfvKwiCvyDHV1ZcyUo=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=A5BQy8SltePE+L+VTIE1A+cua405WkH2PfgQ0evuObbT0kZ3ZY9OynFo+5t75II0Mhnpthiza5uzYttooA3QB15RFzeBJzdpnrD24X6GMdv9unkvXTVZExO5HPD66/TeDtRKM+zzgcma+LXq1Z0WdTm49F7pmYwpdPuub36GldI= 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 [172.19.163.235]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTPS id 4bYJZf4gjMzYQtdc; Fri, 4 Jul 2025 11:11:54 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.128]) by mail.maildlp.com (Postfix) with ESMTP id 7F8801A0EA9; Fri, 4 Jul 2025 11:11:53 +0800 (CST) Received: from [10.67.109.79] (unknown [10.67.109.79]) by APP4 (Coremail) with SMTP id gCh0CgA37Lx5RmdoRWNgAg--.12441S2; Fri, 04 Jul 2025 11:11:53 +0800 (CST) Message-ID: <8dae8006-e63d-467f-bb7c-e8470878e534@huaweicloud.com> Date: Fri, 4 Jul 2025 11:11:52 +0800 Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH next] sched,freezer: prevent tasks from escaping being frozen From: Chen Ridong To: =?UTF-8?Q?Michal_Koutn=C3=BD?= Cc: peterz@infradead.org, rafael@kernel.org, pavel@kernel.org, timvp@google.com, tj@kernel.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, lujialin4@huawei.com, chenridong@huawei.com References: <20250703133427.3301899-1-chenridong@huaweicloud.com> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-CM-TRANSID:gCh0CgA37Lx5RmdoRWNgAg--.12441S2 X-Coremail-Antispam: 1UD129KBjvJXoW7Aw1rKw4DJw4xWF17Kw1xZrb_yoW8Kr1fpr WrWa1UG3Z7trs2yrn2qw4vqws8K392yF4UGr95CrWxJa1YqasIgr4Ik3yYkF1jvryxArnF qF4jq3s7AayUZaDanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUv0b4IE77IF4wAFF20E14v26r4j6ryUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_tr0E3s1l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Gr1j6F4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x 0267AKxVW0oVCq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG 6I80ewAv7VC0I7IYx2IY67AKxVWUGVWUXwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFV Cjc4AY6r1j6r4UM4x0Y48IcVAKI48JM4IIrI8v6xkF7I0E8cxan2IY04v7MxkF7I0En4kS 14v26r1q6r43MxAIw28IcxkI7VAKI48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E5I 8CrVAFwI0_Jr0_Jr4lx2IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWUtVW8 ZwCIc40Y0x0EwIxGrwCI42IY6xIIjxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY1x 0267AKxVW8JVWxJwCI42IY6xAIw20EY4v20xvaj40_Jr0_JF4lIxAIcVC2z280aVAFwI0_ Jr0_Gr1lIxAIcVC2z280aVCY1x0267AKxVW8JVW8JrUvcSsGvfC2KfnxnUUI43ZEXa7IUb mii3UUUUU== X-CM-SenderInfo: hfkh02xlgr0w46kxt4xhlfz01xgou0bp/ On 2025/7/4 11:02, Chen Ridong wrote: > > > On 2025/7/4 1:01, Michal Koutný wrote: >> Hello Ridong. >> >> On Thu, Jul 03, 2025 at 01:34:27PM +0000, Chen Ridong wrote: >>> 2. The cgroup freezer state changes to FROZEN (Can be triggered by reading >>> freezer.state). >> /o\ >> >>> 3. freezing() is called and returns false. >> >> I can see how this can happen because freezer_lock != freezer_mutex. >> >>> As a result, the task may escape being frozen when it should be. >>> >>> To fix this, move the setting of the FROZEN flag to occur just before >>> schedule(). This ensures the flag is only set when we're certain the >>> task must be switched out. >> >> Is it sufficient? (If the task is spuriously woken up, the next >> iteration in that refrigerator loop would be subject to same race, no?) >> >> Thanks, >> Michal > > Hi, Michal: > > Regarding your question: Did you mean that the task was frozen, received > another signal to wake up, but should have remained frozen instead of > entering the running state? > > For this scenario, the solution I've found is that the task can only > break out of the frozen state when its cgroup is thawed. The code > modification would look like the following, and we'll need to add the > cgroup_thawed(p) function: > Sorry, the code should look like: --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -71,19 +71,20 @@ bool __refrigerator(bool check_kthr_stop) for (;;) { bool freeze; - raw_spin_lock_irq(¤t->pi_lock); - WRITE_ONCE(current->__state, TASK_FROZEN); - /* unstale saved_state so that __thaw_task() will wake us up */ - current->saved_state = TASK_RUNNING; - raw_spin_unlock_irq(¤t->pi_lock); - spin_lock_irq(&freezer_lock); - freeze = freezing(current) && !(check_kthr_stop && kthread_should_stop()); + freeze = (freezing(current) || !cgroup_thawed(current)) + && !(check_kthr_stop && kthread_should_stop()); spin_unlock_irq(&freezer_lock); if (!freeze) break; + raw_spin_lock_irq(¤t->pi_lock); + WRITE_ONCE(current->__state, TASK_FROZEN); + /* unstale saved_state so that __thaw_task() will wake us up */ + current->saved_state = TASK_RUNNING; + raw_spin_unlock_irq(¤t->pi_lock); + was_frozen = true; schedule(); } Best regards, Ridong