linux-kernel - Re: [PATCH V2 1/1] nvme: fix multiple ctrl removal scheduling

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Message-ID: <20170526100613.GE24894@localhost.localdomain>
Date:   Fri, 26 May 2017 06:06:14 -0400
From:   Keith Busch <keith.busch@...el.com>
To:     Rakesh Pandit <rakesh@...era.com>
Cc:     linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Jens Axboe <axboe@...com>, Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>
Subject: Re: [PATCH V2 1/1] nvme: fix multiple ctrl removal scheduling

On Wed, May 24, 2017 at 05:26:25PM +0300, Rakesh Pandit wrote:
> Commit c5f6ce97c1210 tries to address multiple resets but fails as
> work_busy doesn't involve any synchronization and can fail.  This is
> reproducible easily as can be seen by WARNING below which is triggered
> with line:
> 
> WARN_ON(dev->ctrl.state == NVME_CTRL_RESETTING)
> 
> Allowing multiple resets can result in multiple controller removal as
> well if different conditions inside nvme_reset_work fail and which
> might deadlock on device_release_driver.
> 
> This patch makes sure that work queue item (reset_work) is added only
> if controller state != NVME_CTRL_RESETTING and that is achieved by
> moving state change outside nvme_reset_work into nvme_reset and
> removing old work_busy call.  State change is always synchronizated
> using controller spinlock.

So, the reason the state is changed when the work is running rather than
queueing is for the window when the state may be set to NVME_CTRL_DELETING,
and we don't want the reset work to proceed in that case.

What do you think about adding a new state, like NVME_CTRL_SCHED_RESET,
then leaving the NVME_CTRL_RESETTING state change as-is?