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Date:   Thu, 16 Aug 2018 08:15:59 -0600
From:   Keith Busch <keith.busch@intel.com>
To:     Michal Wnukowski <wnukowski@google.com>
Cc:     "torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
        "axboe@fb.com" <axboe@fb.com>, "hch@lst.de" <hch@lst.de>,
        "keith.busch@linux.intel.com" <keith.busch@linux.intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>,
        "sagi@grimberg.me" <sagi@grimberg.me>,
        "yigitfiliz@google.com" <yigitfiliz@google.com>
Subject: Re: [PATCH v2] Bugfix for handling of shadow doorbell buffer.
Message-ID: <20180816141558.GB5438@localhost.localdomain>
References: <CA+55aFxOc7_s-BbWJx-kyit-pH9m5fQJk6MSMJ57tFFvMtNh-w@mail.gmail.com>
 <20180815225157.89523-1-wnukowski@google.com>
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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@intel.com>