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Subject: Re: [PATCH v3] blk-cgroup: Use cond_resched() when destroy blkgs
To:     Baolin Wang <baolin.wang@linux.alibaba.com>, tj@kernel.org
Cc:     joseph.qi@linux.alibaba.com, linux-block@vger.kernel.org,
        cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
References: <0be1a0a03367f7230497a2e7a5ed47d2a2d5ae1a.1611809091.git.baolin.wang@linux.alibaba.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <9087d02b-ef9b-46c4-6933-82bb3e520597@kernel.dk>
Date:   Thu, 28 Jan 2021 07:32:03 -0700
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On 1/27/21 10:58 PM, 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(), or the system can accumulate a
> huge number of blkgs in pathological cases. We can add a need_resched()
> check on each loop and release locks and do cond_resched() if true
> 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

Thanks, applied.

-- 
Jens Axboe