linux-kernel - Re: [PATCH v4 2/8] nvme-tcp: Update number of hardware queues before using them

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Message-ID: <20210809085250.xguvx5qiv2gxcoqk@carbon>
Date:   Mon, 9 Aug 2021 10:52:50 +0200
From:   Daniel Wagner <dwagner@...e.de>
To:     Sagi Grimberg <sagi@...mberg.me>
Cc:     linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        James Smart <james.smart@...adcom.com>,
        Keith Busch <kbusch@...nel.org>,
        Ming Lei <ming.lei@...hat.com>, Hannes Reinecke <hare@...e.de>,
        Wen Xiong <wenxiong@...ibm.com>
Subject: Re: [PATCH v4 2/8] nvme-tcp: Update number of hardware queues before
 using them

Hi Sagi,

On Fri, Aug 06, 2021 at 12:57:17PM -0700, Sagi Grimberg wrote:
> > -	ret = nvme_tcp_start_io_queues(ctrl);
> > -	if (ret)
> > -		goto out_cleanup_connect_q;
> > -
> > -	if (!new) {
> > -		nvme_start_queues(ctrl);
> > +	} else if (prior_q_cnt != ctrl->queue_count) {
> 
> So if the queue count did not change we don't wait to make sure
> the queue g_usage_counter ref made it to zero? What guarantees that it
> did?

Hmm, good point. we should always call nvme_wait_freeze_timeout()
for !new queues. Is this what you are implying?


> >   		if (!nvme_wait_freeze_timeout(ctrl, NVME_IO_TIMEOUT)) {
> >   			/*
> >   			 * If we timed out waiting for freeze we are likely to
> > @@ -1828,6 +1822,10 @@ static int nvme_tcp_configure_io_queues(struct nvme_ctrl *ctrl, bool new)
> >   		nvme_unfreeze(ctrl);
> >   	}
> > +	ret = nvme_tcp_start_io_queues(ctrl);
> > +	if (ret)
> > +		goto out_cleanup_connect_q;
> > +
> 
> Did you test this with both heavy I/O, reset loop and ifdown/ifup
> loop?

Not sure if this classifies as heavy I/O (on 80 CPU machine)

fio --rw=readwrite --name=test --filename=/dev/nvme16n1 --size=50M \
    --direct=1 --bs=4k --numjobs=40 --group_reporting --runtime=4h \
    --time_based

and then I installed iptables rules to block the traffic on the
controller side. With this test it is pretty easily to get
the host hanging. Let me know what test you would like to see
from me. I am glad to try to get them running.

> If we unquiesce and unfreeze before we start the queues the pending I/Os
> may resume before the connect and not allow the connect to make forward
> progress.

So the unfreeze should happen after the connect call? What about the
newly created queues? Do they not suffer from the same problem? Isn't
the NVME_TCP_Q_LIVE flag not enough?

Daniel