linux-kernel - Re: [PATCH 0/2] nvme-fc: fix schedule in atomic context

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Message-ID: <16476728-c964-4912-983e-446a44004314@flourine.local>
Date: Thu, 20 Feb 2025 09:00:46 +0100
From: Daniel Wagner <dwagner@...e.de>
To: Keith Busch <kbusch@...nel.org>
Cc: Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>, 
	Sagi Grimberg <sagi@...mberg.me>, James Smart <james.smart@...adcom.com>, 
	Hannes Reinecke <hare@...e.de>, Shinichiro Kawasaki <shinichiro.kawasaki@....com>, 
	linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] nvme-fc: fix schedule in atomic context

On Fri, Feb 14, 2025 at 09:02:02AM +0100, Daniel Wagner wrote:
> Shinichiro reported [1] the recent change in the nvme-fc setup path [2]
> introduced a bug. I didn't spot the schedule call in
> nvme_change_ctrl_state.
> 
> It turns out the locking is not necessary if we make the state machine a
> bit more restrictive and only allow entering the LIVE state from
> CONNECTING. If we do this, it's possible to ensure we either enter LIVE
> only if there was no connection loss event. Also the connection loss
> event handler should always trigger the reset handler to avoid a
> read-write race on the state machine state variable.
> 
> I've tried to replicate the original problem once again and wrote a new
> blktest which tries to trigger the race condition. I let it run a for a
> while and nothing broke, but I can't be sure it is really gone. The rest
> of the blktests also passed. Unfortunatly, the test box with FC hardware
> is currently not working, so I can't test this with real hardware.
> 
> [1] https://lore.kernel.org/all/denqwui6sl5erqmz2gvrwueyxakl5txzbbiu3fgebryzrfxunm@iwxuthct377m/
> [2] https://lore.kernel.org/all/20250109-nvme-fc-handle-com-lost-v4-3-fe5cae17b492@kernel.org/

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