From mboxrd@z Thu Jan 1 00:00:00 1970 From: Baolin Wang Subject: Re: [PATCH] blk-cgroup: Use cond_resched() when destroy blkgs Date: Thu, 28 Jan 2021 09:35:40 +0800 Message-ID: References: <8f4fb91ced02e58ef425189c83214086f1154a0c.1611664710.git.baolin.wang@linux.alibaba.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: List-ID: Content-Type: text/plain; charset="utf-8"; format="flowed" To: Tejun Heo Cc: axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org, joseph.qi-KPsoFbNs7GizrGE5bRqYAgC/G2K4zDHf@public.gmane.org, linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Hi Tejun, > Hello, Baolin. > > On Tue, Jan 26, 2021 at 09:33:25PM +0800, Baolin Wang wrote: >> On !PREEMPT kernel, we can get below softlockup when doing stress >> testing with creating and destroying block cgroup repeatly. The >> reason is it may take a long time to acquire the queue's lock in >> the loop of blkcg_destroy_blkgs(), thus we can use cond_resched() >> instead of cpu_relax() to avoid this issue, since the >> blkcg_destroy_blkgs() is not called from atomic contexts. >> >> [ 4757.010308] watchdog: BUG: soft lockup - CPU#11 stuck for 94s! >> [ 4757.010698] Call trace: >> [ 4757.010700]  blkcg_destroy_blkgs+0x68/0x150 >> [ 4757.010701]  cgwb_release_workfn+0x104/0x158 >> [ 4757.010702]  process_one_work+0x1bc/0x3f0 >> [ 4757.010704]  worker_thread+0x164/0x468 >> [ 4757.010705]  kthread+0x108/0x138 >> >> Signed-off-by: Baolin Wang > > * Can you please add might_sleep() at the top of the function? Sure. > > * Given that the system can accumulate a huge number of blkgs in > pathological cases, I wonder whether a better way to go about it is > explicitly testing need_resched() on each loop and release locks and do > cond_resched() if true? Yes, sound better to to me and will update in next version. Thanks for your sugestion.