linux-kernel - Re: [PATCH] nvme: fix deadlock between reset and scan

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Message-ID: <ZWTa0DJmcLKHRWWC@kbusch-mbp.dhcp.thefacebook.com>
Date:   Mon, 27 Nov 2023 11:07:12 -0700
From:   Keith Busch <kbusch@...nel.org>
To:     Bitao Hu <yaoma@...ux.alibaba.com>
Cc:     axboe@...nel.dk, hch@....de, sagi@...mberg.me,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kanie@...ux.alibaba.com
Subject: Re: [PATCH] nvme: fix deadlock between reset and scan

On Thu, Nov 23, 2023 at 07:00:13PM +0800, Bitao Hu wrote:
> @@ -3631,6 +3631,11 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, struct nvme_ns_info *info)
>  		goto out_unlink_ns;
>  
>  	down_write(&ctrl->namespaces_rwsem);
> +	/* preventing adding ns during resetting */
> +	if (unlikely(ctrl->state != NVME_CTRL_LIVE)) {

We can't rely on ctrl->state for preventing deadlocks. Reading unlocked
ctrl->state is often used, but should be considered advisory-only since
the state could change immediatly after reading it.

> +		up_write(&ctrl->namespaces_rwsem);
> +		goto out_unlink_ns;
> +	}
>  	nvme_ns_add_to_ctrl_list(ns);
>  	up_write(&ctrl->namespaces_rwsem);
>  	nvme_get_ctrl(ctrl);