Subject: Re: Write I/O queue hangup at random on recent Linus' kernels
From:   Jens Axboe <axboe@kernel.dk>
To:     "Kenneth R. Crudup" <kenny@panix.com>
Cc:     linux-bcache@vger.kernel.org, linux-block@vger.kernel.org,
        linux-ext4@vger.kernel.org, linux-nvme@lists.infradead.org,
        Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>
References: <b3ba57a7-d363-9c17-c4be-9dbe86875@panix.com>
 <b9c2681f-e63a-4d3b-913d-d8a75e2c2ea0@kernel.dk>
 <be6a783-97db-c3bf-b16f-e8c62b14755d@panix.com>
 <17206ea6-506d-b1de-09e8-c935ff308bd6@kernel.dk>
Message-ID: <903be817-4118-f34e-1b35-a0108045590f@kernel.dk>
Date:   Fri, 26 Nov 2021 09:53:15 -0700
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On 11/25/21 2:07 PM, Jens Axboe wrote:
> On 11/25/21 2:05 PM, Kenneth R. Crudup wrote:
>>
>> On Tue, 23 Nov 2021, Jens Axboe wrote:
>>
>>> It looks like some missed accounting. You can just disable wbt for now, would
>>> be a useful data point to see if that fixes it. Just do:
>>
>>> echo 0 > /sys/block/nvme0n1/queue/wbt_lat_usec
>>
>>> and that will disable writeback throttling on that device.
>>
>> It's been about 48 hours and haven't seen the issue since doing this.
> 
> Great, thanks for verifying. From your report 5.16-rc2 has the issue, is
> 5.15 fine?

Can you apply this on top of 5.16-rc2 or current -git and see if it fixes
it for you?

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 8799fa73ef34..8874a63ae952 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -860,13 +860,14 @@ void blk_mq_end_request_batch(struct io_comp_batch *iob)
 		if (iob->need_ts)
 			__blk_mq_end_request_acct(rq, now);
 
+		rq_qos_done(rq->q, rq);
+
 		WRITE_ONCE(rq->state, MQ_RQ_IDLE);
 		if (!refcount_dec_and_test(&rq->ref))
 			continue;
 
 		blk_crypto_free_request(rq);
 		blk_pm_mark_last_busy(rq);
-		rq_qos_done(rq->q, rq);
 
 		if (nr_tags == TAG_COMP_BATCH || cur_hctx != rq->mq_hctx) {
 			if (cur_hctx)

-- 
Jens Axboe