linux-kernel - Re: [PATCH -next V5] blk-mq: fix tag

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Date:   Thu, 27 Jan 2022 10:04:54 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Jens Axboe <axboe@...nel.dk>, Laibin Qiu <qiulaibin@...wei.com>
Cc:     ming.lei@...hat.com, john.garry@...wei.com,
        martin.petersen@...cle.com, hare@...e.de,
        akpm@...ux-foundation.org, bvanassche@....org,
        andriy.shevchenko@...ux.intel.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next V5] blk-mq: fix tag_get wait task can't be awakened

On 1/27/22 09:28, Jens Axboe wrote:
> On 1/26/22 6:32 PM, Guenter Roeck wrote:
>> Hi,
>>
>> On Thu, Jan 13, 2022 at 10:55:36AM +0800, Laibin Qiu wrote:
>>> In case of shared tags, there might be more than one hctx which
>>> allocates from the same tags, and each hctx is limited to allocate at
>>> most:
>>>          hctx_max_depth = max((bt->sb.depth + users - 1) / users, 4U);
>>>
>>> tag idle detection is lazy, and may be delayed for 30sec, so there
>>> could be just one real active hctx(queue) but all others are actually
>>> idle and still accounted as active because of the lazy idle detection.
>>> Then if wake_batch is > hctx_max_depth, driver tag allocation may wait
>>> forever on this real active hctx.
>>>
>>> Fix this by recalculating wake_batch when inc or dec active_queues.
>>>
>>> Fixes: 0d2602ca30e41 ("blk-mq: improve support for shared tags maps")
>>> Suggested-by: Ming Lei <ming.lei@...hat.com>
>>> Suggested-by: John Garry <john.garry@...wei.com>
>>> Signed-off-by: Laibin Qiu <qiulaibin@...wei.com>
>>
>> I understand this problem has been reported already, but still:
>>
>> This patch causes a hang in several of my qemu emulations when
>> trying to boot from usb. Reverting it fixes the problem. Bisect log
>> is attached.
>>
>> Boot logs are available at
>> https://kerneltests.org/builders/qemu-arm-aspeed-master/builds/230/steps/qemubuildcommand/logs/stdio
>> but don't really show much: the affected tests simply hang until they
>> are aborted.
> 
> This one got reported a few days ago, can you check if applying:
> 
> https://git.kernel.dk/cgit/linux-block/commit/?h=block-5.17&id=10825410b956dc1ed8c5fbc8bbedaffdadde7f20
> 
> fixes it for you?
> 
Yes, it does.

Thanks,
Guenter