From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) (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 CD415567F; Thu, 25 Jul 2024 01:48:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721872130; cv=none; b=d7MJcysbLxP83VDeizsWkIJN9dJOjk2fWP8nynKMPw7CZQz6HcUbEhSi75CuklQGmc0qIPb5yaAzVRMOQ8gyNa0skZTzwMuO5/1UlkDvrcE6UBXEoOHgg20jE8yI5cyjGwPfplv/sFcCPcLyc1JwKURXKp+hNJubfeBDylYCg9o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721872130; c=relaxed/simple; bh=ZOqUap9ZIFAa0oA5dK3qqGY70Hb+gcTYUSfSf/CUZ1o=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=llQTy+ctgwb4Nhvg+v8lmmhSOcTG8l4XaY9a3NAvpMwPm+vhgtWgvvaMKOWbd6rZvedDStjPdpRyyf5FQf7QaSy4vmwS8YOhlA4LBR+2bYQItiYCM9rTZxy5PS5x6MwICOGg8+Xi1v4emQna24Q3xjEWKH6oqPz87nsYq/R9+tU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.188 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.163.252]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4WTtzG4NRDzMqrD; Thu, 25 Jul 2024 09:46:50 +0800 (CST) Received: from kwepemd100013.china.huawei.com (unknown [7.221.188.163]) by mail.maildlp.com (Postfix) with ESMTPS id 0A70D180088; Thu, 25 Jul 2024 09:48:38 +0800 (CST) Received: from [10.67.109.79] (10.67.109.79) by kwepemd100013.china.huawei.com (7.221.188.163) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1258.34; Thu, 25 Jul 2024 09:48:37 +0800 Message-ID: <53ed023b-c86c-498a-b1fc-2b442059f6af@huawei.com> Date: Thu, 25 Jul 2024 09:48:36 +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 -v2] cgroup: fix deadlock caused by cgroup_mutex and cpu_hotplug_lock To: Hillf Danton CC: Roman Gushchin , , , , References: <20240724110834.2010-1-hdanton@sina.com> Content-Language: en-US From: chenridong In-Reply-To: <20240724110834.2010-1-hdanton@sina.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To kwepemd100013.china.huawei.com (7.221.188.163) On 2024/7/24 19:08, Hillf Danton wrote: > On Fri, 19 Jul 2024 02:52:32 +0000 Chen Ridong >> We found a hung_task problem as shown below: >> >> INFO: task kworker/0:0:8 blocked for more than 327 seconds. >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. >> task:kworker/0:0 state:D stack:13920 pid:8 ppid:2 flags:0x00004000 >> Workqueue: events cgroup_bpf_release >> Call Trace: >> >> __schedule+0x5a2/0x2050 >> ? find_held_lock+0x33/0x100 >> ? wq_worker_sleeping+0x9e/0xe0 >> schedule+0x9f/0x180 >> schedule_preempt_disabled+0x25/0x50 >> __mutex_lock+0x512/0x740 >> ? cgroup_bpf_release+0x1e/0x4d0 >> ? cgroup_bpf_release+0xcf/0x4d0 >> ? process_scheduled_works+0x161/0x8a0 >> ? cgroup_bpf_release+0x1e/0x4d0 >> ? mutex_lock_nested+0x2b/0x40 >> ? __pfx_delay_tsc+0x10/0x10 >> mutex_lock_nested+0x2b/0x40 >> cgroup_bpf_release+0xcf/0x4d0 >> ? process_scheduled_works+0x161/0x8a0 >> ? trace_event_raw_event_workqueue_execute_start+0x64/0xd0 >> ? process_scheduled_works+0x161/0x8a0 >> process_scheduled_works+0x23a/0x8a0 >> worker_thread+0x231/0x5b0 >> ? __pfx_worker_thread+0x10/0x10 >> kthread+0x14d/0x1c0 >> ? __pfx_kthread+0x10/0x10 >> ret_from_fork+0x59/0x70 >> ? __pfx_kthread+0x10/0x10 >> ret_from_fork_asm+0x1b/0x30 >> >> >> This issue can be reproduced by the following methods: >> 1. A large number of cpuset cgroups are deleted. >> 2. Set cpu on and off repeatly. >> 3. Set watchdog_thresh repeatly. >> >> The reason for this issue is cgroup_mutex and cpu_hotplug_lock are >> acquired in different tasks, which may lead to deadlock. >> It can lead to a deadlock through the following steps: >> 1. A large number of cgroups are deleted, which will put a large >> number of cgroup_bpf_release works into system_wq. The max_active >> of system_wq is WQ_DFL_ACTIVE(256). When cgroup_bpf_release can not >> get cgroup_metux, it may cram system_wq, and it will block work >> enqueued later. >> 2. Setting watchdog_thresh will hold cpu_hotplug_lock.read and put >> smp_call_on_cpu work into system_wq. However it may be blocked by >> step 1. >> 3. Cpu offline requires cpu_hotplug_lock.write, which is blocked by step 2. >> 4. When a cpuset is deleted, cgroup release work is placed on >> cgroup_destroy_wq, it will hold cgroup_metux and acquire >> cpu_hotplug_lock.read. Acquiring cpu_hotplug_lock.read is blocked by >> cpu_hotplug_lock.write as mentioned by step 3. Finally, it forms a >> loop and leads to a deadlock. >> >> cgroup_destroy_wq(step4) cpu offline(step3) WatchDog(step2) system_wq(step1) >> ...... >> __lockup_detector_reconfigure: >> P(cpu_hotplug_lock.read) >> ... >> ... >> percpu_down_write: >> P(cpu_hotplug_lock.write) >> ...256+ works >> cgroup_bpf_release: >> P(cgroup_mutex) >> smp_call_on_cpu: >> Wait system_wq >> ... >> css_killed_work_fn: >> P(cgroup_mutex) >> ... >> cpuset_css_offline: >> P(cpu_hotplug_lock.read) >> > worker_thread() > manage_workers() > maybe_create_worker() > create_worker() // has nothing to do with WQ_DFL_ACTIVE > process_scheduled_works() > > Given idle worker created independent of WQ_DFL_ACTIVE before handling > work item, no deadlock could rise in your scenario above. Hello Hillf, did you mean to say this issue couldn't happen? I wish it hadn't happen, as it took me a long time to figure out. However, it did happen. It could be reproduced with the method I offered, You can access the scripts using this link: https://lore.kernel.org/cgroups/e90c32d2-2a85-4f28-9154-09c7d320cb60@huawei.com/T/#t. It's not about how the pool's workers were created, but rather the limit(system_wq ) of workqueue. If system_wq reaches its max_active limit, the work enqueued afterward will be placed on pwq->inactive_works. In this scenario described above, the problem is all active works(cgroup_bpf_release) are blocked, and the inactive_works(smp_call_on_cpu) couldn't be executed when it forms a loop. We have discussed this before in V1, you can find in the Link. Thanks Ridong