nvmf/rdma host crash during heavy load and keep alive recovery

[Steve Wise]

> >
> > >> Can you also give patch [1] a try? It's not a solution, but I want
> > >> to see if it hides the problem...
> > >>
> > >
> > > hmm.  I ran the experiment once with [1] and it didn't crash.  I ran
> it a 2nd
> > > time and hit a new crash.  Maybe a problem with [1]?
> >
> > Strange, I don't see how we can visit rdma_destroy_qp twice given
> > that we have NVME_RDMA_IB_QUEUE_ALLOCATED bit protecting it.
> >
> > Not sure if it fixes anything, but we probably need it regardless, can
> > you give another go with this on top:
> 
> Still hit it with this on top (had to tweak the patch a little).
> 
> Steve.

So with this patch, the crash is a little different.  One thread is in the usual
place crashed in nvme_rdma_post_send() called by nvme_rdma_queue_rq() because
the qp and cm_id in the nvme_rdma_queue have been freed.   Actually there are a
handful of CPUs processing different requests in the same type stack trace.  But
perhaps that is expected given the work load and number of controllers (10) and
queues (32 per controller)...

I also see another worker thread here:

PID: 3769   TASK: ffff880e18972f40  CPU: 3   COMMAND: "kworker/3:3"
 #0 [ffff880e2f7938d0] __schedule at ffffffff816dfa17
 #1 [ffff880e2f793930] schedule at ffffffff816dff00
 #2 [ffff880e2f793980] schedule_timeout at ffffffff816e2b1b
 #3 [ffff880e2f793a60] wait_for_completion_timeout at ffffffff816e0f03
 #4 [ffff880e2f793ad0] destroy_cq at ffffffffa061d8f3 [iw_cxgb4]
 #5 [ffff880e2f793b60] c4iw_destroy_cq at ffffffffa061dad5 [iw_cxgb4]
 #6 [ffff880e2f793bf0] ib_free_cq at ffffffffa0360e5a [ib_core]
 #7 [ffff880e2f793c20] nvme_rdma_destroy_queue_ib at ffffffffa0644e9b
[nvme_rdma]
 #8 [ffff880e2f793c60] nvme_rdma_stop_and_free_queue at ffffffffa0645083
[nvme_rdma]
 #9 [ffff880e2f793c80] nvme_rdma_reconnect_ctrl_work at ffffffffa0645a9f
[nvme_rdma]
#10 [ffff880e2f793cb0] process_one_work at ffffffff810a1613
#11 [ffff880e2f793d90] worker_thread at ffffffff810a22ad
#12 [ffff880e2f793ec0] kthread at ffffffff810a6dec
#13 [ffff880e2f793f50] ret_from_fork at ffffffff816e3bbf

I'm trying to identify if this reconnect is for the same controller that crashed
processing a request.  It probably is, but I need to search the stack frame to
try and find the controller pointer...

Steve.