netdev - Re: [Intel-wired-lan] [PATCH net] igb: re-assign hw address pointer on reset after PCI error

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Date:   Wed, 9 Nov 2016 09:12:37 -0800
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     "Guilherme G. Piccoli" <gpiccoli@...ux.vnet.ibm.com>
Cc:     intel-wired-lan <intel-wired-lan@...ts.osuosl.org>,
        Netdev <netdev@...r.kernel.org>,
        "Fujinaka, Todd" <todd.fujinaka@...el.com>
Subject: Re: [Intel-wired-lan] [PATCH net] igb: re-assign hw address pointer
 on reset after PCI error

On Mon, Oct 31, 2016 at 1:12 PM, Guilherme G. Piccoli
<gpiccoli@...ux.vnet.ibm.com> wrote:
> Whenever the igb driver detects the result of a read operation returns
> a value composed only by F's (like 0xFFFFFFFF), it will detach the
> net_device, clear the hw_addr pointer and warn to the user that adapter's
> link is lost - those steps happen on igb_rd32().
>
> In case a PCI error happens on Power architecture, there's a recovery
> mechanism called EEH, that will reset the PCI slot and call driver's
> handlers to reset the adapter and network functionality as well.
>
> We observed that once hw_addr is NULL after the error is detected on
> igb_rd32(), it's never assigned back, so in the process of resetting
> the network functionality we got a NULL pointer dereference in both
> igb_configure_tx_ring() and igb_configure_rx_ring(). In order to avoid
> such bug, we re-assign the hw_addr value in the beginning of the
> function igb_reset(), in case the hw_addr is NULL when we reach that
> path.
>
> Reported-by: Anthony H. Thai <ahthai@...ibm.com>
> Reported-by: Harsha Thyagaraja <hathyaga@...ibm.com>
> Signed-off-by: Guilherme G. Piccoli <gpiccoli@...ux.vnet.ibm.com>
> ---
>  drivers/net/ethernet/intel/igb/igb_main.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
> index edc9a6a..c19119c 100644
> --- a/drivers/net/ethernet/intel/igb/igb_main.c
> +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> @@ -1873,6 +1873,13 @@ void igb_reset(struct igb_adapter *adapter)
>         struct e1000_fc_info *fc = &hw->fc;
>         u32 pba, hwm;
>
> +       /* In case of PCI error, adapter might have lost its HW
> +        * address; if we reached this point after an error scenario,
> +        * we should re-assign the hw_addr based on the saved io_addr.
> +        */
> +       if (!hw->hw_addr)
> +               hw->hw_addr = adapter->io_addr;
> +
>         /* Repartition Pba for greater than 9k mtu
>          * To take effect CTRL.RST is required.
>          */

It seems like this would have the potential to get noisy pretty
quickly since every reset would retrigger this.

It might make more sense to move this line into igb_io_slot_reset and
igb_resume where the device would have gone through a reset of some
sort and then had the state of the device restored and the device
memory access was re-enabled via pci_enable_device_mem.  Also there is
no point in really doing the "if" since you should always be okay to
overwrite hw->hw_addr with adapter->io_addr.

Thanks.

- Alex