From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga04-in.huawei.com (szxga04-in.huawei.com [45.249.212.190]) (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 526A813D51E; Thu, 1 Aug 2024 01:35:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.190 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722476105; cv=none; b=Yz2AlbWH9yKPJ6ls+2PT9m5WLzWFvfS7Mn3SmFMRPESL81Ldvllxod57RpS1Q/qBVRJ+J7ndtcMmWMf9AFNBbmu2/p8mYCXYM1nZNrXJF0I38s6XZe0c0XZFWY6QFA0pBXwo0q0Ffv2/OSHKtgrns/qQyd2iDfHfjRwbp4nMg2U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722476105; c=relaxed/simple; bh=OTctEdVmE9ePZfx9ef7wplwiI5URhWRMOI7lkcfON3M=; h=Message-ID:Date:MIME-Version:Subject:From:To:CC:References: In-Reply-To:Content-Type; b=jn/9ZlQcrKTqehipFDdZ+XYchkmDJM9WwLZORu2mFGnBZ2/rByGCwryP9Foa4O0RgWUndKisnm++k/bhXbNpf8oQHa9UJs/ERtwxvbd+mN+TbODbAChN/jzOZuWPUuGS/3hcFtQQISTkizuDVTVB0tSFF48sUErPgEw6gTG+TIM= 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=45.249.212.190 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 [172.19.163.44]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4WZBH33NPLz2Clgw; Thu, 1 Aug 2024 09:30:23 +0800 (CST) Received: from kwepemd100013.china.huawei.com (unknown [7.221.188.163]) by mail.maildlp.com (Postfix) with ESMTPS id 392C514013B; Thu, 1 Aug 2024 09:34:58 +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, 1 Aug 2024 09:34:57 +0800 Message-ID: <823a5926-4ed9-4784-b9ae-ee0d0eb8ebf8@huawei.com> Date: Thu, 1 Aug 2024 09:34:56 +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 From: chenridong To: , , , , , , , , , , , , , , , , =?UTF-8?Q?Michal_Koutn=C3=BD?= CC: , , References: <20240719025232.2143638-1-chenridong@huawei.com> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To kwepemd100013.china.huawei.com (7.221.188.163) On 2024/7/24 8:53, chenridong wrote: > > > On 2024/7/19 10:52, Chen Ridong wrote: >> 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) >> >> To fix the problem, place cgroup_bpf_release works on cgroup_destroy_wq, >> which can break the loop and solve the problem. System wqs are for misc >> things which shouldn't create a large number of concurrent work items. >> If something is going to generate >WQ_DFL_ACTIVE(256) concurrent work >> items, it should use its own dedicated workqueue. >> >> Fixes: 4bfc0bb2c60e ("bpf: decouple the lifetime of cgroup_bpf from >> cgroup itself") >> Link: >> https://lore.kernel.org/cgroups/e90c32d2-2a85-4f28-9154-09c7d320cb60@huawei.com/T/#t >> Signed-off-by: Chen Ridong >> --- >>   kernel/bpf/cgroup.c             | 2 +- >>   kernel/cgroup/cgroup-internal.h | 1 + >>   kernel/cgroup/cgroup.c          | 2 +- >>   3 files changed, 3 insertions(+), 2 deletions(-) >> >> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c >> index 8ba73042a239..a611a1274788 100644 >> --- a/kernel/bpf/cgroup.c >> +++ b/kernel/bpf/cgroup.c >> @@ -334,7 +334,7 @@ static void cgroup_bpf_release_fn(struct >> percpu_ref *ref) >>       struct cgroup *cgrp = container_of(ref, struct cgroup, bpf.refcnt); >>       INIT_WORK(&cgrp->bpf.release_work, cgroup_bpf_release); >> -    queue_work(system_wq, &cgrp->bpf.release_work); >> +    queue_work(cgroup_destroy_wq, &cgrp->bpf.release_work); >>   } >>   /* Get underlying bpf_prog of bpf_prog_list entry, regardless if >> it's through >> diff --git a/kernel/cgroup/cgroup-internal.h >> b/kernel/cgroup/cgroup-internal.h >> index 520b90dd97ec..9e57f3e9316e 100644 >> --- a/kernel/cgroup/cgroup-internal.h >> +++ b/kernel/cgroup/cgroup-internal.h >> @@ -13,6 +13,7 @@ >>   extern spinlock_t trace_cgroup_path_lock; >>   extern char trace_cgroup_path[TRACE_CGROUP_PATH_LEN]; >>   extern void __init enable_debug_cgroup(void); >> +extern struct workqueue_struct *cgroup_destroy_wq; >>   /* >>    * cgroup_path() takes a spin lock. It is good practice not to take >> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c >> index e32b6972c478..3317e03fe2fb 100644 >> --- a/kernel/cgroup/cgroup.c >> +++ b/kernel/cgroup/cgroup.c >> @@ -124,7 +124,7 @@ DEFINE_PERCPU_RWSEM(cgroup_threadgroup_rwsem); >>    * destruction work items don't end up filling up max_active of >> system_wq >>    * which may lead to deadlock. >>    */ >> -static struct workqueue_struct *cgroup_destroy_wq; >> +struct workqueue_struct *cgroup_destroy_wq; >>   /* generate an array of cgroup subsystem pointers */ >>   #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys, > > Friendly ping. > Hi, Tejun,Roman,and Michal, do you have any opinion? Can this patch be merged?