From mboxrd@z Thu Jan  1 00:00:00 1970
From: swise@opengridcomputing.com (Steve Wise)
Date: Thu, 18 Aug 2016 13:50:42 -0500
Subject: nvme/rdma initiator stuck on reboot
In-Reply-To: <01ee01d1f97a$4406d5c0$cc148140$@opengridcomputing.com>
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 <2202d08c-2b4c-3bd9-6340-d630b8e2f8b5@grimberg.me>
 <073301d1f894$5ddb81d0$19928570$@opengridcomputing.com>
 <7c4827ff-21c9-21e9-5577-1bd374305a0b@grimberg.me>
 <075901d1f899$e5cc6f00$b1654d00$@opengridcomputing.com>
 <e2e04664-c374-3745-ecf3-f49ca7a3addf@grimberg.me>
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Message-ID: <027d01d1f981$6c19e9b0$444dbd10$@opengridcomputing.com>

> > Btw, in that case the patch is not actually correct, as even workqueue
> > with a higher concurrency level MAY deadlock under enough memory
> > pressure.  We'll need separate workqueues to handle this case I think.
> >
> > > Yes?  And the
> > > reconnect worker was never completing?  Why is that?  Here are a few
tidbits
> > > about iWARP connections:  address resolution == neighbor discovery.  So if
> the
> > > neighbor is unreachable, it will take a few seconds for the OS to give up
> and
> > > fail the resolution.  If the neigh entry is valid and the peer becomes
> > > unreachable during connection setup, it might take 60 seconds or so for a
> > > connect operation to give up and fail.  So this is probably slowing the
> > > reconnect thread down.   But shouldn't the reconnect thread notice that a
> delete
> > > is trying to happen and bail out?
> >
> > I think we should aim for a state machine that can detect this, but
> > we'll have to see if that will end up in synchronization overkill.
> 
> Looking at the state machine I don't see why the reconnect thread would get
> stuck continually rescheduling once the controller was deleted.  Changing from
> RECONNECTING to DELETING will be done by nvme_change_ctrl_state().  So once
> that
> happens, in __nvme_rdma_del_ctrl() , the thread running reconnect logic should
> stop rescheduling due to this in the failure logic of
> nvme_rdma_reconnect_ctrl_work():
> 
> ...
> requeue:
>         /* Make sure we are not resetting/deleting */
>         if (ctrl->ctrl.state == NVME_CTRL_RECONNECTING) {
>                 dev_info(ctrl->ctrl.device,
>                         "Failed reconnect attempt, requeueing...\n");
>                 queue_delayed_work(nvme_rdma_wq, &ctrl->reconnect_work,
>                                         ctrl->reconnect_delay * HZ);
>         }
> ...
> 
> So something isn't happening like I think it is, I guess.


I see what happens.  Assume the 10 controllers are reconnecting and failing,
thus they reschedule each time.  I then run a script to delete all 10 devices
sequentially.  Like this:

for i in $(seq 1 10); do nvme disconnect -d nvme${i}n1; done

The first device, nvme1n1 gets a disconnect/delete command and changes the
controller state from RECONNECTING to DELETING, and then schedules
nvme_rdma_del_ctrl_work(), but that is stuck behind the 9 others continually
reconnecting, failing, and rescheduling.  I'm not sure why the delete never gets
run though?  I would think if it is scheduled, then it would get executed before
the reconnect threads rescheduling?  Maybe we need some round-robin mode for our
workq?  And because the first delete is stuck, none of the subsequent delete
commands get executed.  Note: If I run each disconnect command in the
background, then they all get cleaned up ok.   Like this:

for i in $(seq 1 10); do nvme disconnect -d nvme${i}n1 & done