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

[Keith Busch]

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@xxxxxxxxx>