linux-kernel - Re: [RFC PATCH] nvme: prevent hang on surprise removal of NVMe disk

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Date:   Tue, 15 Feb 2022 19:47:04 +0100
From:   Christoph Hellwig <hch@....de>
To:     Keith Busch <kbusch@...nel.org>
Cc:     Markus Blöchl <markus.bloechl@...tronik.com>,
        Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        linux-nvme@...ts.infradead.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Stefan Roese <sr@...x.de>
Subject: Re: [RFC PATCH] nvme: prevent hang on surprise removal of NVMe disk

On Tue, Feb 15, 2022 at 07:22:40AM -0800, Keith Busch wrote:
> I can't actually tell if not checking the DYING flag check was
> intentional or not, since the comments in blk_queue_start_drain() say
> otherwise.
> 
> Christoph, do you know the intention here? Should __bio_queue_enter()
> check the queue DYING flag, or do you prefer drivers explicity set the
> disk state like this? It looks to me the queue flags should be checked
> since that's already tied to the freeze wait_queue_head_t.

It was intentional but maybe not fully thought out.  Do you remember why
we're doing the manual setting of the dying flag instead of just calling
del_gendisk early on in nvme?  Because calling del_gendisk is supposed
to be all that a tree needs to do.