Subject: Re: Write I/O queue hangup at random on recent Linus' kernels
To:     "Kenneth R. Crudup" <kenny@panix.com>,
        linux-bcache@vger.kernel.org, linux-block@vger.kernel.org,
        linux-ext4@vger.kernel.org, linux-nvme@lists.infradead.org
References: <b3ba57a7-d363-9c17-c4be-9dbe86875@panix.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <b9c2681f-e63a-4d3b-913d-d8a75e2c2ea0@kernel.dk>
Date:   Tue, 23 Nov 2021 16:27:33 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <b3ba57a7-d363-9c17-c4be-9dbe86875@panix.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 11/23/21 2:05 PM, Kenneth R. Crudup wrote:
> 
> (Please forgive the SPAMmy nature of the To: list; I'm not exactly sure whose
> subsystem this issue belongs to, so please trim as appropriate).
> 
> I've got a Kioxia NVMe SSD on my Dell XPS-7390 2-in-1 running an i7-1065G7 CPU
> with 32GB RAM.  If you need more info (and I suspect so), please let me know.
> 
> I'm sorry I don't have a better description of the problem, but I run Linus'
> master branch (and sometimes I weed out problems like this). I'm current as of
> his commit 1360572566 (the 5.16-rc2 tag).
> 
> For about two weeks now every now and then my block/NVMe/...? subsystem comes to
> a total halt on writes, and I get a system that can no longer issue writes
> (reads/pageins still seem to work) until I reboot. SysRq-S/U/B still leaves a
> dirty ext4 filesystem requring recovery on reboot.
> 
> It happens at random- twice today as a matter of fact- and there doesn't seem to
> be any particular action that causes it:

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.

I'll take a look at this, but most likely not until start next week...

-- 
Jens Axboe