linux-kernel - Re: nvme-fc: Question about __nvme_fc_abort_outstanding

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Message-ID: <Z38tZ99hIX2stF8L@fedora>
Date: Thu, 9 Jan 2025 09:59:03 +0800
From: Ming Lei <ming.lei@...hat.com>
To: Mohamed Khalfella <mkhalfella@...estorage.com>
Cc: James Smart <james.smart@...adcom.com>, Keith Busch <kbusch@...nel.org>,
	Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
	Sagi Grimberg <sagi@...mberg.me>, linux-nvme@...ts.infradead.org,
	linux-kernel@...r.kernel.org, randyj@...estorage.com,
	jrani@...estorage.com
Subject: Re: nvme-fc: Question about __nvme_fc_abort_outstanding_ios()

On Wed, Jan 08, 2025 at 05:32:10PM -0800, Mohamed Khalfella wrote:
> Hello,
> 
> I was looking at this code and I had a question about it.
> 
> drivers/nvme/host/fc.c
> 2473 static void
> 2474 __nvme_fc_abort_outstanding_ios(struct nvme_fc_ctrl *ctrl, bool start_queues)
> 2475 {
> ...
> ...
> 2503                 blk_mq_tagset_busy_iter(&ctrl->tag_set,
> 2504                                 nvme_fc_terminate_exchange, &ctrl->ctrl);
> 2505                 blk_mq_tagset_wait_completed_request(&ctrl->tag_set);
> 
> nvme_fc_terminate_exchange() calls __nvme_fc_abort_op() to abort all active
> ops with status FCPOP_STATE_ACTIVE. I think these active ops map to in-flight
> requests MQ_RQ_IN_FLIGHT. After blk_mq_tagset_busy_iter() returns it is not
> guaranteed that all ops had done callback functions called on them. Some
> of these requests might still be in-flight.
> 
> blk_mq_tagset_wait_completed_request() makes sure that we do not have pending
> completed requests, but it does not check for in-flight requests?

It is because many callbacks call blk_mq_complete_request() to complete
request, and the request may be completed remotely via IPI, that is why
blk_mq_tagset_wait_completed_request() is needed.


Thanks, 
Ming