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

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Date:   Thu, 16 Aug 2018 14:20:08 -0700
From:   Sagi Grimberg <sagi@...mberg.me>
To:     Michal Wnukowski <wnukowski@...gle.com>,
        torvalds@...ux-foundation.org
Cc:     axboe@...com, hch@....de, keith.busch@...el.com,
        keith.busch@...ux.intel.com, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, yigitfiliz@...gle.com
Subject: Re: [PATCH v2] Bugfix for handling of shadow doorbell buffer.


> 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;
>   	}

Reviewed-by: Sagi Grimberg <sagi@...mberg.me>