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From:   Jens Axboe <axboe@kernel.dk>
To:     Hugh Dickins <hughd@google.com>
Cc:     Keith Busch <kbusch@kernel.org>, linux-block@vger.kernel.org,
        Liu Song <liusong@linux.alibaba.com>,
        Hillf Danton <hdanton@sina.com>, Jan Kara <jack@suse.cz>,
        linux-kernel@vger.kernel.org, Yu Kuai <yukuai1@huaweicloud.com>
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Subject: Re: [PATCH next v3] sbitmap: fix lockup while swapping
Message-Id: <166449592135.4485.5114483552637281957.b4-ty@kernel.dk>
Date:   Thu, 29 Sep 2022 17:58:41 -0600
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On Thu, 29 Sep 2022 12:50:12 -0700 (PDT), Hugh Dickins wrote:
> Commit 4acb83417cad ("sbitmap: fix batched wait_cnt accounting")
> is a big improvement: without it, I had to revert to before commit
> 040b83fcecfb ("sbitmap: fix possible io hung due to lost wakeup")
> to avoid the high system time and freezes which that had introduced.
> 
> Now okay on the NVME laptop, but 4acb83417cad is a disaster for heavy
> swapping (kernel builds in low memory) on another: soon locking up in
> sbitmap_queue_wake_up() (into which __sbq_wake_up() is inlined), cycling
> around with waitqueue_active() but wait_cnt 0 .  Here is a backtrace,
> showing the common pattern of outer sbitmap_queue_wake_up() interrupted
> before setting wait_cnt 0 back to wake_batch (in some cases other CPUs
> are idle, in other cases they're spinning for a lock in dd_bio_merge()):
> 
> [...]

Applied, thanks!

[1/1] sbitmap: fix lockup while swapping
      commit: 30514bd2dd4e86a3ecfd6a93a3eadf7b9ea164a0

Best regards,
-- 
Jens Axboe