linux-kernel - Re: [PATCH] nvme-pci: use NOWAIT flag for nvme_set_host

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Date:   Mon, 29 Jan 2018 16:06:13 +0800
From:   "jianchao.wang" <jianchao.w.wang@...cle.com>
To:     keith.busch@...el.com, axboe@...com, hch@....de, sagi@...mberg.me
Cc:     linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org
Subject: Re: [PATCH] nvme-pci: use NOWAIT flag for nvme_set_host_mem



On 01/29/2018 11:07 AM, Jianchao Wang wrote:
> nvme_set_host_mem will invoke nvme_alloc_request without NOWAIT
> flag, it is unsafe for nvme_dev_disable. The adminq driver tags
> may have been used up when the previous outstanding adminq requests
> cannot be completed due to some hardware error. We have to depend
> on the timeout path to complete the previous outstanding adminq
> requests and free the tags.
> However, nvme_timeout will invoke nvme_dev_disable and try to
> get the shutdown_lock which is held by another context who is
> sleeping to wait for the tags to be freed by timeout path. A
> deadlock comes up.
> 
> To fix it, let nvme_set_host_mem use NOWAIT flag.

In fact, this is the only case about nvme_set_host_mem in
nvme_dev_disable.
Consider the following case:

A adminq request expired.

timeout_work context
nvme_timeout
  -> nvme_dev_disable
    -> nvme_set_host_mem
    if this adminq request expires again, the timeout_work
    cannot handle this case, because it is waiting for the
    result of nvme_set_host_mem.

Thanks
Jianchao