Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 29 Jan 2018 13:17:16 -0700
From:   Keith Busch <keith.busch@intel.com>
To:     Sagi Grimberg <sagi@grimberg.me>
Cc:     Jianchao Wang <jianchao.w.wang@oracle.com>, axboe@fb.com,
        hch@lst.de, linux-nvme@lists.infradead.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] nvme-pci: use NOWAIT flag for nvme_set_host_mem
Message-ID: <20180129201716.GB25515@localhost.localdomain>
References: <1517195255-21832-1-git-send-email-jianchao.w.wang@oracle.com>
 <20180129160145.GA25515@localhost.localdomain>
 <1b7d3700-945f-9272-b6aa-d2ebeaf0cb1e@grimberg.me>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1b7d3700-945f-9272-b6aa-d2ebeaf0cb1e@grimberg.me>
User-Agent: Mutt/1.9.1 (2017-09-22)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, Jan 29, 2018 at 09:55:41PM +0200, Sagi Grimberg wrote:
> > Thanks for the fix. It looks like we still have a problem, though.
> > Commands submitted with the "shutdown_lock" held need to be able to make
> > forward progress without relying on a completion, but this one could
> > block indefinitely.
> 
> Can you explain to me why is the shutdown_lock needed to synchronize
> nvme_dev_disable? More concretely, how is nvme_dev_disable different
> from other places where we rely on the ctrl state to serialize stuff?
> 
> The only reason I see would be to protect against completion-after-abort
> scenario but I think the block layer should protect against it (checks
> if the request timeout timer fired).

We can probably find a way to use the state machine for this. Disabling
the controller pre-dates the state machine, and the mutex is there to
protect against two actors shutting the controller down at the same
time, like a hot removal at the same time as a timeout handling reset.