From patchwork Sat Aug 17 09:33:34 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: chenridong X-Patchwork-Id: 13767089 X-Patchwork-Delegate: bpf@iogearbox.net 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 6FB6D14600F; Sat, 17 Aug 2024 09:41:12 +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=1723887674; cv=none; b=tkGWm+L1h8thLl5+Y/zks4BCThr2WpQMaDvGjpECn35UIn4r7OJzH2cjsgJ8brqf5oWD9KhLgZb9a/0CA7RWTZZ2FW8hBYi1LuHdJAvPIBHeiVxs4mY5820c1AlkEIrIK2fz77xWTNVMUCebRh3sxDJVpAYpCpgv/njsqlDEz5A= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723887674; c=relaxed/simple; bh=e/6eO58p0hU4BqE/P+CYc0FUTo4UyWBoKSiNKG6ov9k=; h=From:To:CC:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=OnKlicAsUHYTZ+AoBXFFtieV2iLXHHAO5Kr/1ZFkQKTRH3N6+JABEzN82IfxUqE2LEQYLBr9jwXoH9eYqMfdUz2Rv9wq7Jq2XrpyDFezj/wKn+OFhifbZyeZSNto0yi4D0MJHqU7frW5cLZlzowMK85QTmZpjg97ecpg83Ztbc8= 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 [172.19.88.234]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4WmDJG34lqz2Cmhg; Sat, 17 Aug 2024 17:36:14 +0800 (CST) Received: from kwepemd100013.china.huawei.com (unknown [7.221.188.163]) by mail.maildlp.com (Postfix) with ESMTPS id 393A81401E9; Sat, 17 Aug 2024 17:41:10 +0800 (CST) Received: from huawei.com (10.67.174.121) 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; Sat, 17 Aug 2024 17:41:09 +0800 From: Chen Ridong To: , , , , , , , , , , , , , , , CC: , , Subject: [PATCH v3 1/1] cgroup: fix deadlock caused by cgroup_mutex and cpu_hotplug_lock Date: Sat, 17 Aug 2024 09:33:34 +0000 Message-ID: <20240817093334.6062-2-chenridong@huawei.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240817093334.6062-1-chenridong@huawei.com> References: <20240817093334.6062-1-chenridong@huawei.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To kwepemd100013.china.huawei.com (7.221.188.163) X-Patchwork-Delegate: bpf@iogearbox.net 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 pressuse test: 1. A large number of cpuset cgroups are deleted. 2. Set cpu on and off repeatly. 3. Set watchdog_thresh repeatly. The scripts can be obtained at LINK mentioned above the signature. 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 cpusets are deleted asynchronously, which puts a large number of cgroup_bpf_release works into system_wq. The max_active of system_wq is WQ_DFL_ACTIVE(256). Consequently, all active works are cgroup_bpf_release works, and many cgroup_bpf_release works will be put into inactive queue. As illustrated in the diagram, there are 256 (in the acvtive queue) + n (in the inactive queue) works. 2. Setting watchdog_thresh will hold cpu_hotplug_lock.read and put smp_call_on_cpu work into system_wq. However step 1 has already filled system_wq, 'sscs.work' is put into inactive queue. 'sscs.work' has to wait until the works that were put into the inacvtive queue earlier have executed (n cgroup_bpf_release), so it will be blocked for a while. 3. Cpu offline requires cpu_hotplug_lock.write, which is blocked by step 2. 4. Cpusets that were deleted at step 1 put cgroup_release works into cgroup_destroy_wq. They are competing to get cgroup_mutex all the time. When cgroup_metux is acqured by work at css_killed_work_fn, it will call cpuset_css_offline, which needs to acqure cpu_hotplug_lock.read. However, cpuset_css_offline will be blocked for step 3. 5. At this moment, there are 256 works in active queue that are cgroup_bpf_release, they are attempting to acquire cgroup_mutex, and as a result, all of them are blocked. Consequently, sscs.work can not be executed. Ultimately, this situation leads to four processes being blocked, forming a deadlock. system_wq(step1) WatchDog(step2) cpu offline(step3) cgroup_destroy_wq(step4) ... 2000+ cgroups deleted asyn 256 actives + n inactives __lockup_detector_reconfigure P(cpu_hotplug_lock.read) put sscs.work into system_wq 256 + n + 1(sscs.work) sscs.work wait to be executed warting sscs.work finish percpu_down_write P(cpu_hotplug_lock.write) ...blocking... css_killed_work_fn P(cgroup_mutex) cpuset_css_offline P(cpu_hotplug_lock.read) ...blocking... 256 cgroup_bpf_release mutex_lock(&cgroup_mutex); ..blocking... 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 Reviewed-by: Michal Koutný --- 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 c964dd7ff967..17ac19bc8106 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 75058fbf4450..77fa9ed69c86 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,