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Subject: Re: [PATCH] nvme-pci: use NOWAIT flag for nvme_set_host_mem
To:     Keith Busch <keith.busch@intel.com>,
        Jianchao Wang <jianchao.w.wang@oracle.com>
Cc:     axboe@fb.com, hch@lst.de, linux-nvme@lists.infradead.org,
        linux-kernel@vger.kernel.org
References: <1517195255-21832-1-git-send-email-jianchao.w.wang@oracle.com>
 <20180129160145.GA25515@localhost.localdomain>
From:   Sagi Grimberg <sagi@grimberg.me>
Message-ID: <1b7d3700-945f-9272-b6aa-d2ebeaf0cb1e@grimberg.me>
Date:   Mon, 29 Jan 2018 21:55:41 +0200
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Hey Keith,

> 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).