From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) (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 C361028FD; Wed, 24 Jul 2024 00:53:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.189 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721782420; cv=none; b=ttIDHpTusrIjA2Rf2kIkG//68YiipPLrvm/kNni3w1L7BpNZ22Wo0DFouuSVyuUmM68Zb0+EE/AFTtxMAfbB+2lbOwFLIDwm5LkMGEoCIZeugv4U40OmmKrtOBHKatoCoqHdXTXiwUFAn0Akr3XhOZOFD0O04L28rOVKiGJ1Ne8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721782420; c=relaxed/simple; bh=H7Z9Sy5C9QluRaOVOhSXM/dPEdUmz4QH30oBCXALxgk=; h=Message-ID:Date:MIME-Version:Subject:From:To:CC:References: In-Reply-To:Content-Type; b=qpxHcFKEcE5fIL7DF4XYqKyefTAgwS6CoYjsvrnV/HaMC62p+kLSJaTcQj6XvAnkeopaq7q2P4zcs2VV5cgn+FKntMh4tQHsF7GTxcULHzZLou3kah578zMuuoDIxVhKpOKOZFuHVxEGzaZDX/GzFMvyL3L+Dfb40uAzMKqtktA= 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=45.249.212.189 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 [172.19.88.105]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4WTFlQ5YmLzQmPP; Wed, 24 Jul 2024 08:49:22 +0800 (CST) Received: from kwepemd100013.china.huawei.com (unknown [7.221.188.163]) by mail.maildlp.com (Postfix) with ESMTPS id 8312F140485; Wed, 24 Jul 2024 08:53:33 +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; Wed, 24 Jul 2024 08:53:32 +0800 Message-ID: Date: Wed, 24 Jul 2024 08:53:31 +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: , , , , , , , , , , , , , , , CC: , , References: <20240719025232.2143638-1-chenridong@huawei.com> Content-Language: en-US In-Reply-To: <20240719025232.2143638-1-chenridong@huawei.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To kwepemd100013.china.huawei.com (7.221.188.163) 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.