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

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Message-ID: <1b7d3700-945f-9272-b6aa-d2ebeaf0cb1e@grimberg.me>
Date:   Mon, 29 Jan 2018 21:55:41 +0200
From:   Sagi Grimberg <sagi@...mberg.me>
To:     Keith Busch <keith.busch@...el.com>,
        Jianchao Wang <jianchao.w.wang@...cle.com>
Cc:     axboe@...com, hch@....de, linux-nvme@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvme-pci: use NOWAIT flag for nvme_set_host_mem

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).