linux-kernel - Re: [PATCH] nvme: avoid missing db ring during reset

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Message-ID: <b6880ffc-4ce5-49cd-b08d-de2c82b21f4f@gmail.com>
Date: Sat, 26 Apr 2025 00:35:24 +0800
From: Linjun Bao <meljbao@...il.com>
To: Keith Busch <kbusch@...nel.org>
Cc: Jens Axboe <axboe@...com>, Christoph Hellwig <hch@....de>,
 Sagi Grimberg <sagi@...mberg.me>, linux-kernel@...r.kernel.org,
 linux-nvme@...ts.infradead.org
Subject: Re: [PATCH] nvme: avoid missing db ring during reset



On 4/25/2025 11:48 PM, Keith Busch wrote:
> On Fri, Apr 25, 2025 at 08:01:45PM +0800, Linjun Bao wrote:
>> During nvme reset, there is a rare case, when user admin cmd such
>> as smart-log and nvme_admin_create_sq from nvme_setup_io_queues
>> happen to in the same blk_mq dispatch list, and the user cmd is
>> the last one. nvme_admin_create_sq is dispatched first in
>> nvme_queue_rq(), nvme_write_sq_db() is called but immediately
>> returns without writing the doorbell because it's not masked
>> "last". The subsequent smart-log ioctl fails fast hitting
>> nvme_fail_nonready_cmd(), skipping both nvme_sq_copy_cmd() and
>> nvme_write_sq_db(), so no doorbell write ever occurs. The
>> nvme_admin_create_sq fails timeout finally.
> 
> The block layer is supposed to call the driver's commit_rqs() function
> if anything in the dispatch list wasn't successful, which should notify
> the controller of any pending SQEs. Is that not happening here?

Yes, in this case, the last user admin cmd will fail nvme_host_path_errror
finally, but ret BLK_STS_OK, which will let blk_mq_dispatch_rq_list skips 
the commit_rqs, thus missing updating the SQ doorbell.