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 3C31C187FEE; Fri, 27 Sep 2024 09:50:56 +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=1727430659; cv=none; b=hoIhMS8Yw8bf8sAWgvcDF3eQkC2VeVBGqvn5y7b+GNbDmRw4G8qPWWgSMyqF3UD6+lPuzQaBMyPuKzZaUVtKMeoQTu0jHSa8NPA7XHHYN66qW74fbR3Vs5ttb9pXlUr+0VgpO7kB3NIsXg1l0+b6Aw3CSVbiVeuknkb/UvKbEg4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727430659; c=relaxed/simple; bh=/DWH+WZXk7PC9u/Ait8jHc5bLQKJGCBwTC2MmP/783E=; h=Message-ID:Date:MIME-Version:Subject:To:References:Cc:From: In-Reply-To:Content-Type; b=m+mQWoMBzXM6tQ3e6TFZHFhqfxhCYme9mAnZVdZn4g3XngYfHrw64F2QBtQu7ee3i0fSc9JShKIcLl+CXQkIHHR6c2piNMhvGTN8JrEKdQOdE27pTXorLwtXviRfKx+X+yZfaLPJkboGF/E/Dxevi64/T0lyfiThwvnhRCLasck= 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 [172.19.93.142]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTP id 4XFQh066YBz4f3jq6; Fri, 27 Sep 2024 17:50:40 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.75]) by mail.maildlp.com (Postfix) with ESMTP id 275841A07BA; Fri, 27 Sep 2024 17:50:52 +0800 (CST) Received: from [10.67.109.79] (unknown [10.67.109.79]) by APP2 (Coremail) with SMTP id Syh0CgCHvGH5f_ZmOhXoCQ--.32277S2; Fri, 27 Sep 2024 17:50:50 +0800 (CST) Message-ID: <22f11b9d-a33e-4ff4-8cb4-01b865069ce7@huaweicloud.com> Date: Fri, 27 Sep 2024 17:50:49 +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 v5 1/3] cgroup/bpf: use a dedicated workqueue for cgroup bpf destruction To: Vishal Chourasia , "tj@kernel.org >> Tejun Heo" , Zefan Li , Waiman Long , =?UTF-8?Q?Michal_Koutn=C3=BD?= References: <20240923114352.4001560-2-chenridong@huaweicloud.com> Content-Language: en-US Cc: cgroups@vger.kernel.org, LKML From: Chen Ridong In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CM-TRANSID:Syh0CgCHvGH5f_ZmOhXoCQ--.32277S2 X-Coremail-Antispam: 1UD129KBjvAXoWfJr1rCw47WF47WF48XrWkZwb_yoW8Jr13to WrXF1kJa1kWr1UJ3WrJwnrX3y3uws2ga9rAr1Ygr4DA3W8Wry5trn8GF13J3yfXF1jyF4k ZFy3Xa45Zw1DJwn5n29KB7ZKAUJUUUU8529EdanIXcx71UUUUU7v73VFW2AGmfu7bjvjm3 AaLaJ3UjIYCTnIWjp_UUU5M7kC6x804xWl14x267AKxVW8JVW5JwAFc2x0x2IEx4CE42xK 8VAvwI8IcIk0rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2ocxC64kIII0Yj41l84x0c7CEw4 AK67xGY2AK021l84ACjcxK6xIIjxv20xvE14v26F1j6w1UM28EF7xvwVC0I7IYx2IY6xkF 7I0E14v26F4j6r4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x 0267AKxVW0oVCq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG 6I80ewAv7VC0I7IYx2IY67AKxVWUGVWUXwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFV Cjc4AY6r1j6r4UM4x0Y48IcVAKI48JMxkF7I0En4kS14v26r126r1DMxAIw28IcxkI7VAK I48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E5I8CrVAFwI0_Jr0_Jr4lx2IqxVCjr7 xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWUAVWUtwCIc40Y0x0EwIxGrwCI42IY6xII jxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY1x0267AKxVW8JVWxJwCI42IY6xAIw2 0EY4v20xvaj40_Jr0_JF4lIxAIcVC2z280aVAFwI0_Jr0_Gr1lIxAIcVC2z280aVCY1x02 67AKxVW8JVW8JrUvcSsGvfC2KfnxnUUI43ZEXa7IUbiF4tUUUUU== X-CM-SenderInfo: hfkh02xlgr0w46kxt4xhlfz01xgou0bp/ On 2024/9/27 12:22, Vishal Chourasia wrote: > On Mon, Sep 23, 2024 at 11:43:50AM +0000, Chen Ridong wrote: >> I 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. >> 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 a dedicated >> workqueue 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 > Tested-by: Vishal Chourasia > > Thank you Chen, for sharing the details on how to reproduce, and for the > patchset. > > Steps I followed to reproduce: > 1) run cgroup-make.sh > 2) run hotplug.sh > 3) run watchdog.sh > > # cat cgroup-make.sh > #!/bin/bash > > echo 30 > /proc/sys/kernel/hung_task_timeout_secs > cat /proc/sys/kernel/hung_task_timeout_secs > > echo +cpuset > /sys/fs/cgroup/cgroup.subtree_control > mkdir /sys/fs/cgroup/memory > # echo +memory > /sys/fs/cgroup/memory/cgroup.subtree_control > mkdir /sys/fs/cgroup/cpuset > echo +cpuset > /sys/fs/cgroup/cpuset/cgroup.subtree_control > echo +cpu > /sys/fs/cgroup/cpuset/cgroup.subtree_control > > > timestamp=$(date +%s) > echo $timestamp > while true; do > for i in {0..2000}; do > mkdir /sys/fs/cgroup/cpuset/test${timestamp}_${i} & > mkdir /sys/fs/cgroup/memory/test${timestamp}_${i} & > done > > for i in {0..2000}; do > rmdir /sys/fs/cgroup/cpuset/test${timestamp}_${i} & > rmdir /sys/fs/cgroup/memory/test${timestamp}_${i} & > done > done > > # cat hotplug.sh > #!/bin/bash > > while true > do > echo 1 > /sys/devices/system/cpu/cpu2/online > echo 1 > /sys/devices/system/cpu/cpu3/online > echo 0 > /sys/devices/system/cpu/cpu2/online > echo 0 > /sys/devices/system/cpu/cpu3/online > done > > # cat watchdog.sh > #!/bin/bash > > while true > do > echo 12 > /proc/sys/kernel/watchdog_thresh > echo 11 > /proc/sys/kernel/watchdog_thresh > echo 10 > /proc/sys/kernel/watchdog_thresh > done > > With these steps I able to get the hung_task timeout log messages > INFO: task kworker/7:1:84 blocked for more than 30 seconds. > Not tainted 6.11.0-chenridong_base-10547-g684a64bf32b6-dirty #59 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:kworker/7:1 state:D stack:0 pid:84 tgid:84 ppid:2 flags:0x00000000 > Workqueue: events cgroup_bpf_release > Call Trace: > [c00000000ee779a0] [c00000000ee779e0] 0xc00000000ee779e0 (unreliable) > [c00000000ee77b50] [c00000000001f79c] __switch_to+0x14c/0x220 > [c00000000ee77bb0] [c0000000010e8cd0] __schedule+0x2c0/0x840 > [c00000000ee77c90] [c0000000010e9290] schedule+0x40/0x110 > [c00000000ee77d00] [c0000000010e95b0] schedule_preempt_disabled+0x20/0x30 > [c00000000ee77d20] [c0000000010ec408] __mutex_lock.constprop.0+0x5e8/0xbe0 > [c00000000ee77db0] [c000000000472f58] cgroup_bpf_release+0x98/0x3d0 > [c00000000ee77e40] [c0000000001886a8] process_one_work+0x1f8/0x520 > [c00000000ee77ef0] [c00000000018a01c] worker_thread+0x33c/0x4f0 > [c00000000ee77f90] [c0000000001970c8] kthread+0x138/0x140 > [c00000000ee77fe0] [c00000000000dd58] start_kernel_thread+0x14/0x18 > INFO: task kworker/4:1:98 blocked for more than 30 seconds. > Not tainted 6.11.0-chenridong_base-10547-g684a64bf32b6-dirty #59 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:kworker/4:1 state:D stack:0 pid:98 tgid:98 ppid:2 flags:0x00000000 > Workqueue: events cgroup_bpf_release > Call Trace: > [c00000000ee1f9a0] [c00000000ee1f9e0] 0xc00000000ee1f9e0 (unreliable) > [c00000000ee1fb50] [c00000000001f79c] __switch_to+0x14c/0x220 > [c00000000ee1fbb0] [c0000000010e8cd0] __schedule+0x2c0/0x840 > [c00000000ee1fc90] [c0000000010e9290] schedule+0x40/0x110 > [c00000000ee1fd00] [c0000000010e95b0] schedule_preempt_disabled+0x20/0x30 > [c00000000ee1fd20] [c0000000010ec408] __mutex_lock.constprop.0+0x5e8/0xbe0 > [c00000000ee1fdb0] [c000000000472f58] cgroup_bpf_release+0x98/0x3d0 > [c00000000ee1fe40] [c0000000001886a8] process_one_work+0x1f8/0x520 > [c00000000ee1fef0] [c00000000018a01c] worker_thread+0x33c/0x4f0 > [c00000000ee1ff90] [c0000000001970c8] kthread+0x138/0x140 > [c00000000ee1ffe0] [c00000000000dd58] start_kernel_thread+0x14/0x18 > INFO: task kworker/5:1:110 blocked for more than 30 seconds. > Not tainted 6.11.0-chenridong_base-10547-g684a64bf32b6-dirty #59 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:kworker/5:1 state:D stack:0 pid:110 tgid:110 ppid:2 flags:0x00000000 > Workqueue: events cgroup_bpf_release > Call Trace: > [c0000000608bf9a0] [c0000000608bf9e0] 0xc0000000608bf9e0 (unreliable) > [c0000000608bfb50] [c00000000001f79c] __switch_to+0x14c/0x220 > [c0000000608bfbb0] [c0000000010e8cd0] __schedule+0x2c0/0x840 > [c0000000608bfc90] [c0000000010e9290] schedule+0x40/0x110 > [c0000000608bfd00] [c0000000010e95b0] schedule_preempt_disabled+0x20/0x30 > [c0000000608bfd20] [c0000000010ec408] __mutex_lock.constprop.0+0x5e8/0xbe0 > [c0000000608bfdb0] [c000000000472f58] cgroup_bpf_release+0x98/0x3d0 > [c0000000608bfe40] [c0000000001886a8] process_one_work+0x1f8/0x520 > [c0000000608bfef0] [c00000000018a01c] worker_thread+0x33c/0x4f0 > [c0000000608bff90] [c0000000001970c8] kthread+0x138/0x140 > [c0000000608bffe0] [c00000000000dd58] start_kernel_thread+0x14/0x18 > Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings > > After applying this patchset, I didn't see any log messages being > printed in dmesg. > > State of the git repo: > $git log --oneline > a40aebb33934 (HEAD -> patches/v5_20240923_chenridong_add_dedicated_wq_for_cgroup_bpf_and_adjust_wq_max_active) workqueue: Adjust WQ_MAX_ACTIVE from 512 to 2048 > 08a2979a9e59 workqueue: doc: Add a note saturating the system_wq is not permitted > 0e6f5ea2955f cgroup/bpf: use a dedicated workqueue for cgroup bpf destruction > 684a64bf32b6 Merge tag 'nfs-for-6.12-1' of git://git.linux-nfs.org/projects/anna/linux-nfs > > > >> --- >> kernel/bpf/cgroup.c | 18 +++++++++++++++++- >> 1 file changed, 17 insertions(+), 1 deletion(-) >> >> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c >> index e7113d700b87..1a7609f61d44 100644 >> --- a/kernel/bpf/cgroup.c >> +++ b/kernel/bpf/cgroup.c >> @@ -24,6 +24,22 @@ >> DEFINE_STATIC_KEY_ARRAY_FALSE(cgroup_bpf_enabled_key, MAX_CGROUP_BPF_ATTACH_TYPE); >> EXPORT_SYMBOL(cgroup_bpf_enabled_key); >> >> +/* >> + * cgroup bpf destruction makes heavy use of work items and there can be a lot >> + * of concurrent destructions. Use a separate workqueue so that cgroup bpf >> + * destruction work items don't end up filling up max_active of system_wq >> + * which may lead to deadlock. >> + */ >> +static struct workqueue_struct *cgroup_bpf_destroy_wq; >> + >> +static int __init cgroup_bpf_wq_init(void) >> +{ >> + cgroup_bpf_destroy_wq = alloc_workqueue("cgroup_bpf_destroy", 0, 1); >> + WARN_ON_ONCE(!cgroup_bpf_destroy_wq); >> + return 0; >> +} >> +core_initcall(cgroup_bpf_wq_init); >> + >> /* __always_inline is necessary to prevent indirect call through run_prog >> * function pointer. >> */ >> @@ -334,7 +350,7 @@ 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_bpf_destroy_wq, &cgrp->bpf.release_work); >> } >> >> /* Get underlying bpf_prog of bpf_prog_list entry, regardless if it's through >> -- >> 2.34.1 Thank you for doing that. Best regards, Ridong