Re: [PATCH v4 2/4] can: kvaser_usb: Update error counters before exiting on OOM

["Ahmed S. Darwish" <darwish.07@gmail.com>]

On Fri, Jan 16, 2015 at 03:50:40PM +0000, Andri Yngvason wrote:
> See comments below.
> 
> Quoting Ahmed S. Darwish (2015-01-12 20:36:50)
> ...
> > 
> > [ Patch is build-tested, but not _fully_ run-time tested.
> > 
> >   It's based on linux-can/testing commit d642b49f6d84b94bd
> >   "can: kvaser_usb: Don't dereference skb after a netif_rx" ]
> > 
> > Subject: [PATCH] can: kvaser_usb: Update net interface state
> >  before exiting on OOM
> > 
> > From: Ahmed S. Darwish <ahmed.darwish@valeo.com>
> > 
> > Let the network interface can bus state and error counters be
> > more accurate in case of Out of Memory conditions.
> > 
> > Suggested-by: Marc Kleine-Budde <mkl@pengutronix.de>
> > Signed-off-by: Ahmed S. Darwish <ahmed.darwish@valeo.com>
> > ---
> >  drivers/net/can/usb/kvaser_usb.c | 182 +++++++++++++++++++++++----------------
> >  1 file changed, 106 insertions(+), 76 deletions(-)
> > 
> > diff --git a/drivers/net/can/usb/kvaser_usb.c b/drivers/net/can/usb/kvaser_usb.c
> > index c32cd61..2d0ef76 100644
> > --- a/drivers/net/can/usb/kvaser_usb.c
> > +++ b/drivers/net/can/usb/kvaser_usb.c
> > @@ -273,6 +273,10 @@ struct kvaser_msg {
> >         } u;
> >  } __packed;
> >  
> > +struct kvaser_usb_error_summary {
> > +       u8 channel, status, txerr, rxerr, error_factor;
> > +};
> > +
> >  struct kvaser_usb_tx_urb_context {
> >         struct kvaser_usb_net_priv *priv;
> >         u32 echo_index;
> > @@ -615,6 +619,57 @@ static void kvaser_usb_unlink_tx_urbs(struct kvaser_usb_net_priv *priv)
> >                 priv->tx_contexts[i].echo_index = MAX_TX_URBS;
> >  }
> >  
> 
> This function is doing some things that are now be handled by
> can_change_state(). You can make your state handling code a lot shorter by
> using it.
> 
> > +static void kvaser_usb_rx_error_update_state(struct kvaser_usb_net_priv *priv,
> > +                                            const struct kvaser_usb_error_summary *es)
> > +{
> > +       struct net_device_stats *stats;
> > +       unsigned int new_state;
> > +
> > +       stats = &priv->netdev->stats;
> > +       new_state = priv->can.state;
> > +
> > +       netdev_dbg(priv->netdev, "Error status: 0x%02x\n", es->status);
> > +
> > +       if (es->status & M16C_STATE_BUS_OFF) {
> can_change_state() updates the state stats.
> > +               priv->can.can_stats.bus_off++;
> > +               new_state = CAN_STATE_BUS_OFF;
> > +       } else if (es->status & M16C_STATE_BUS_PASSIVE) {
> > +               if (priv->can.state != CAN_STATE_ERROR_PASSIVE) {
> See last comment.
> > +                       priv->can.can_stats.error_passive++;
> > +               }
> > +               new_state = CAN_STATE_ERROR_PASSIVE;
> > +       }
> > +
> > +       if (es->status == M16C_STATE_BUS_ERROR) {
> > +               if ((priv->can.state < CAN_STATE_ERROR_WARNING) &&
> > +                   ((es->txerr >= 96) || (es->rxerr >= 96))) {
> Same as above.
> > +                       priv->can.can_stats.error_warning++;
> > +                       new_state = CAN_STATE_ERROR_WARNING;
> > +               } else if (priv->can.state > CAN_STATE_ERROR_ACTIVE) {
> > +                       new_state = CAN_STATE_ERROR_ACTIVE;
> > +               }
> > +       }
> > +
> > +       if (!es->status) {
> > +               new_state = CAN_STATE_ERROR_ACTIVE;
> > +       }
> > +
> > +       if (priv->can.restart_ms &&
> > +           (priv->can.state >= CAN_STATE_BUS_OFF) &&
> > +           (new_state < CAN_STATE_BUS_OFF)) {
> This is NOT in can_change_state(). Keep it.
> > +               priv->can.can_stats.restarts++;
> > +       }
> > +
> > +       if (es->error_factor) {
> > +               priv->can.can_stats.bus_error++;
> > +               stats->rx_errors++;
> > +       }
> > +
> > +       priv->bec.txerr = es->txerr;
> > +       priv->bec.rxerr = es->rxerr;
> can_change_state() does this too.
> > +       priv->can.state = new_state;
> > +}
> > +
> >  static void kvaser_usb_rx_error(const struct kvaser_usb *dev,
> >                                 const struct kvaser_msg *msg)
> ...
> > -       if (status & M16C_STATE_BUS_RESET) {
> > +       if (es.status & M16C_STATE_BUS_RESET) {
> >                 kvaser_usb_unlink_tx_urbs(priv);
> >                 return;
> >         }
> >  
> OK, maybe we need to move "priv->can.state = new_state" out of
> can_change_state(). See explanation below.
> > +       old_state = priv->can.state;
> > +       kvaser_usb_rx_error_update_state(priv, &es);
> > +       new_state = priv->can.state;
> > +
> >         skb = alloc_can_err_skb(priv->netdev, &cf);
> >         if (!skb) {
> >                 stats->rx_dropped++;
> >                 return;
> >         }
> >  
> You should be able to replace this:
> > -       new_state = priv->can.state;
> > -
> > -       netdev_dbg(priv->netdev, "Error status: 0x%02x\n", status);
> > -
> > -       if (status & M16C_STATE_BUS_OFF) {
> > -               cf->can_id |= CAN_ERR_BUSOFF;
> > -
> > -               priv->can.can_stats.bus_off++;
> > +       if (es.status & M16C_STATE_BUS_OFF) {
> >                 if (!priv->can.restart_ms)
> >                         kvaser_usb_simple_msg_async(priv, CMD_STOP_CHIP);
> > -
> >                 netif_carrier_off(priv->netdev);
> >  
> > -               new_state = CAN_STATE_BUS_OFF;
> > -       } else if (status & M16C_STATE_BUS_PASSIVE) {
> > -               if (priv->can.state != CAN_STATE_ERROR_PASSIVE) {
> > +               cf->can_id |= CAN_ERR_BUSOFF;
> > +       } else if (es.status & M16C_STATE_BUS_PASSIVE) {
> > +               if (old_state != CAN_STATE_ERROR_PASSIVE) {
> >                         cf->can_id |= CAN_ERR_CRTL;
> >  
> > -                       if (txerr || rxerr)
> > -                               cf->data[1] = (txerr > rxerr)
> > +                       if (es.txerr || es.rxerr)
> > +                               cf->data[1] = (es.txerr > es.rxerr)
> >                                                 ? CAN_ERR_CRTL_TX_PASSIVE
> >                                                 : CAN_ERR_CRTL_RX_PASSIVE;
> >                         else
> >                                 cf->data[1] = CAN_ERR_CRTL_TX_PASSIVE |
> >                                               CAN_ERR_CRTL_RX_PASSIVE;
> > -
> > -                       priv->can.can_stats.error_passive++;
> >                 }
> > -
> > -               new_state = CAN_STATE_ERROR_PASSIVE;
> >         }
> >  
> > -       if (status == M16C_STATE_BUS_ERROR) {
> > -               if ((priv->can.state < CAN_STATE_ERROR_WARNING) &&
> > -                   ((txerr >= 96) || (rxerr >= 96))) {
> > +       if (es.status == M16C_STATE_BUS_ERROR) {
> > +               if ((old_state < CAN_STATE_ERROR_WARNING) &&
> > +                   ((es.txerr >= 96) || (es.rxerr >= 96))) {
> >                         cf->can_id |= CAN_ERR_CRTL;
> > -                       cf->data[1] = (txerr > rxerr)
> > +                       cf->data[1] = (es.txerr > es.rxerr)
> >                                         ? CAN_ERR_CRTL_TX_WARNING
> >                                         : CAN_ERR_CRTL_RX_WARNING;
> > -
> > -                       priv->can.can_stats.error_warning++;
> > -                       new_state = CAN_STATE_ERROR_WARNING;
> > -               } else if (priv->can.state > CAN_STATE_ERROR_ACTIVE) {
> > +               } else if (old_state > CAN_STATE_ERROR_ACTIVE) {
> >                         cf->can_id |= CAN_ERR_PROT;
> >                         cf->data[2] = CAN_ERR_PROT_ACTIVE;
> > -
> > -                       new_state = CAN_STATE_ERROR_ACTIVE;
> >                 }
> With something like:
> 	if(new_state != old_state)
> 	{
> 		tx_state = get_tx_state(...);
> 		rx_state = get_rx_state(...);
> 		can_change_state(priv, cf, tx_state, rx_state);
> 		if(new_state == CAN_STATE_BUS_OFF)
> 			bus_off(...);
> 	}
> >         }
> >  
> > -       if (!status) {
> > +       if (!es.status) {
> >                 cf->can_id |= CAN_ERR_PROT;
> >                 cf->data[2] = CAN_ERR_PROT_ACTIVE;
> > -
> > -               new_state = CAN_STATE_ERROR_ACTIVE;
> >         }
> >  
> ...
> 
> I suggest that you create functions named kvaser_get_tx_state and
> kvaser_get_rx_state (or one function that returns to argument if that suits you
> better) based on kvaser_usb_rx_error_update_state.
> 
> Because you want to assign the netlink state before you do the skb alloc, you
> need to make a copy of the netlink state before you change it and reassign the
> old state to the netlink structure after the alloc succeeds. This is because
> can_change_state() relies on priv->can.state for the "current state". This is a
> hack. Perhaps we need to split up can_change_state().
> 

Thanks a lot Andri for your detailed review! I've included changes, similar
in spirit to the above, in the next patch series.

Regards,
Darwish

> See:
> http://article.gmane.org/gmane.linux.can/7164
> http://article.gmane.org/gmane.linux.can/7162
> http://article.gmane.org/gmane.linux.can/7163
> http://article.gmane.org/gmane.linux.can/7167
> 
> Best regards,
> Andri Yngvason