linux-kernel - Re: [PATCH] nvme-rdma: complete requests from ->timeout

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Message-ID: <20181208020201.GD21523@localhost.localdomain>
Date:   Fri, 7 Dec 2018 19:02:01 -0700
From:   Keith Busch <keith.busch@...el.com>
To:     Sagi Grimberg <sagi@...mberg.me>
Cc:     Jaesoo Lee <jalee@...estorage.com>, axboe@...com, hch@....de,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Prabhath Sajeepa <psajeepa@...estorage.com>,
        Roland Dreier <roland@...estorage.com>,
        Ashish Karkare <ashishk@...estorage.com>
Subject: Re: [PATCH] nvme-rdma: complete requests from ->timeout

On Fri, Dec 07, 2018 at 12:05:37PM -0800, Sagi Grimberg wrote:
> 
> > Could you please take a look at this bug and code review?
> > 
> > We are seeing more instances of this bug and found that reconnect_work
> > could hang as well, as can be seen from below stacktrace.
> > 
> >   Workqueue: nvme-wq nvme_rdma_reconnect_ctrl_work [nvme_rdma]
> >   Call Trace:
> >   __schedule+0x2ab/0x880
> >   schedule+0x36/0x80
> >   schedule_timeout+0x161/0x300
> >   ? __next_timer_interrupt+0xe0/0xe0
> >   io_schedule_timeout+0x1e/0x50
> >   wait_for_completion_io_timeout+0x130/0x1a0
> >   ? wake_up_q+0x80/0x80
> >   blk_execute_rq+0x6e/0xa0
> >   __nvme_submit_sync_cmd+0x6e/0xe0
> >   nvmf_connect_admin_queue+0x128/0x190 [nvme_fabrics]
> >   ? wait_for_completion_interruptible_timeout+0x157/0x1b0
> >   nvme_rdma_start_queue+0x5e/0x90 [nvme_rdma]
> >   nvme_rdma_setup_ctrl+0x1b4/0x730 [nvme_rdma]
> >   nvme_rdma_reconnect_ctrl_work+0x27/0x70 [nvme_rdma]
> >   process_one_work+0x179/0x390
> >   worker_thread+0x4f/0x3e0
> >   kthread+0x105/0x140
> >   ? max_active_store+0x80/0x80
> >   ? kthread_bind+0x20/0x20
> > 
> > This bug is produced by setting MTU of RoCE interface to '568' for
> > test while running I/O traffics.
> 
> I think that with the latest changes from Keith we can no longer rely
> on blk-mq to barrier racing completions. We will probably need
> to barrier ourselves in nvme-rdma...

You really need to do that anyway. If you were relying on blk-mq to save
you from double completions by ending a request in the nvme driver while
the lower half can still complete the same one, the only thing preventing
data corruption is the probability the request wasn't reallocated for a
new command.