linux-kernel - Re: [PATCH v2] Bugfix for handling of shadow doorbell buffer.

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Message-ID: <20180816141558.GB5438@localhost.localdomain>
Date:   Thu, 16 Aug 2018 08:15:59 -0600
From:   Keith Busch <keith.busch@...el.com>
To:     Michal Wnukowski <wnukowski@...gle.com>
Cc:     "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "axboe@...com" <axboe@...com>, "hch@....de" <hch@....de>,
        "keith.busch@...ux.intel.com" <keith.busch@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "sagi@...mberg.me" <sagi@...mberg.me>,
        "yigitfiliz@...gle.com" <yigitfiliz@...gle.com>
Subject: Re: [PATCH v2] Bugfix for handling of shadow doorbell buffer.

On Wed, Aug 15, 2018 at 03:51:57PM -0700, Michal Wnukowski wrote:
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index 17a0190bd88f..4452f8553301 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -306,6 +306,14 @@ static bool nvme_dbbuf_update_and_check_event(u16 value, u32 *dbbuf_db,
>  		old_value = *dbbuf_db;
>  		*dbbuf_db = value;
>  
> +		/*
> +		 * Ensure that the doorbell is updated before reading
> +		 * the EventIdx from memory. NVMe controller should have
> +		 * similar ordering guarantees - update EventIdx before
> +		 * reading doorbell.
> +		 */
> +		mb();
> +
>  		if (!nvme_dbbuf_need_event(*dbbuf_ei, value, old_value))
>  			return false;
>  	}

Looks good to me. This should also be a stable candidate.

Reviewed-by: Keith Busch <keith.busch@...el.com>