netdev - RE: [PATCH RESEND 2/2] bnx2x: Fix kernel crash and data miscompare after EEH recovery

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Date:	Wed, 28 May 2014 08:38:04 +0000
From:	Dmitry Kravkov <Dmitry.Kravkov@...gic.com>
To:	"wenxiong@...ux.vnet.ibm.com" <wenxiong@...ux.vnet.ibm.com>,
	David Miller <davem@...emloft.net>
CC:	Ariel Elior <Ariel.Elior@...gic.com>,
	netdev <netdev@...r.kernel.org>, Milton Miller <miltonm@....com>
Subject: RE: [PATCH RESEND 2/2] bnx2x: Fix kernel crash and data miscompare
 after EEH recovery

Hi Wen
> -----Original Message-----
> From: netdev-owner@...r.kernel.org [mailto:netdev-
> owner@...r.kernel.org] On Behalf Of wenxiong@...ux.vnet.ibm.com
> Sent: Tuesday, May 27, 2014 10:11 PM
> To: David Miller
> Cc: Ariel Elior; netdev; Milton Miller; Wen Xiong
> Subject: [PATCH RESEND 2/2] bnx2x: Fix kernel crash and data miscompare
> after EEH recovery
>
> A rmb() is required to ensure that the CQE is not read before it is written by
> the adapter DMA.  PCI ordering rules will make sure the other fields are
> written before the marker at the end of struct eth_fast_path_rx_cqe but
> without rmb() a weakly ordered processor can process stale data.
>
> Without the barrier we have observed various crashes including
> bnx2x_tpa_start being called on queues not stopped (resulting in message
> start of bin not in stop) and NULL pointer exceptions from bnx2x_rx_int.
>
> Signed-off-by: Milton Miller <miltonm@....com>
> Signed-off-by: Wen Xiong <wenxiong@...ux.vnet.ibm.com>
> ---
>  drivers/net/ethernet/broadcom/bnx2x/bnx2x_cmn.c |   12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> Index: b/drivers/net/ethernet/broadcom/bnx2x/bnx2x_cmn.c
> ===================================================================
> --- a/drivers/net/ethernet/broadcom/bnx2x/bnx2x_cmn.c 2014-05-23
> 10:34:21.000000000 -0500
> +++ b/drivers/net/ethernet/broadcom/bnx2x/bnx2x_cmn.c 2014-05-27
> 13:51:12.067764759 -0500
> @@ -906,6 +906,18 @@ static int bnx2x_rx_int(struct bnx2x_fas
>               bd_prod = RX_BD(bd_prod);
>               bd_cons = RX_BD(bd_cons);
>
> +             /* A rmb() is required to ensure that the CQE is not read
> +              * before it is written by the adapter DMA.  PCI ordering
> +              * rules will make sure the other fields are written before
> +              * the marker at the end of struct eth_fast_path_rx_cqe
> +              * but without rmb() a weakly ordered processor can process
> +              * stale data.  Without the barrier we have observed various
> +              * crashes including bnx2x_tpa_start being called on queues
> +              * not stopped (resulting in message start of bin not in
> +              * stop) and NULL pointer exceptions from bnx2x_rx_int.
> +             */
Can you please drop third sentence from the comment or rephrase it in more generic way like:
Without the barrier TPA state-machine might enter inconsistent state and kernel stack might be provided with incorrect packet description - these lead to various kernel crashes.

Thanks
Dmitry
> +             rmb();
> +
>               cqe_fp_flags = cqe_fp->type_error_flags;
>               cqe_fp_type = cqe_fp_flags &
> ETH_FAST_PATH_RX_CQE_TYPE;
>
>
> --
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