Subject: Re: [PATCH net 1/3] slip/slcan: added locking in wakeup function

From: Oliver Hartkopp <[email-masked]>
Date: Fri, 13 Sep 2013 20:45:29 +0200

On 13.09.2013 19:37, Andre Naujoks wrote:
> The locking is needed, since the the internal buffer for the CAN frames is
> changed during the wakeup call. This could cause buffer inconsistencies
> under high loads, especially for the outgoing short CAN packet skbuffs.
> 
> The needed locks led to deadlocks before commit
> "5ede52538ee2b2202d9dff5b06c33bfde421e6e4 tty: Remove extra wakeup from pty
> write() path", which removed the direct callback to the wakeup function from the
> tty layer.
> 
> As slcan.c is based on slip.c the issue in the original code is fixed, too.
> 
> Signed-off-by: Andre Naujoks <[email-masked]>

At least for slcan.c:

Acked-by: Oliver Hartkopp <[email-masked]>

Tnx for figuring that out with your heavy load testing.

Best regards,
Oliver

> ---
>  drivers/net/can/slcan.c | 3 +++
>  drivers/net/slip/slip.c | 3 +++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/drivers/net/can/slcan.c b/drivers/net/can/slcan.c
> index 874188b..d571e2e 100644
> --- a/drivers/net/can/slcan.c
> +++ b/drivers/net/can/slcan.c
> @@ -286,11 +286,13 @@ static void slcan_write_wakeup(struct tty_struct *tty)
>  	if (!sl || sl->magic != SLCAN_MAGIC || !netif_running(sl->dev))
>  		return;
>  
> +	spin_lock(&sl->lock);
>  	if (sl->xleft <= 0)  {
>  		/* Now serial buffer is almost free & we can start
>  		 * transmission of another packet */
>  		sl->dev->stats.tx_packets++;
>  		clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
> +		spin_unlock(&sl->lock);
>  		netif_wake_queue(sl->dev);
>  		return;
>  	}
> @@ -298,6 +300,7 @@ static void slcan_write_wakeup(struct tty_struct *tty)
>  	actual = tty->ops->write(tty, sl->xhead, sl->xleft);
>  	sl->xleft -= actual;
>  	sl->xhead += actual;
> +	spin_unlock(&sl->lock);
>  }
>  
>  /* Send a can_frame to a TTY queue. */
> diff --git a/drivers/net/slip/slip.c b/drivers/net/slip/slip.c
> index a34d6bf..cc70ecf 100644
> --- a/drivers/net/slip/slip.c
> +++ b/drivers/net/slip/slip.c
> @@ -429,11 +429,13 @@ static void slip_write_wakeup(struct tty_struct *tty)
>  	if (!sl || sl->magic != SLIP_MAGIC || !netif_running(sl->dev))
>  		return;
>  
> +	spin_lock(&sl->lock);
>  	if (sl->xleft <= 0)  {
>  		/* Now serial buffer is almost free & we can start
>  		 * transmission of another packet */
>  		sl->dev->stats.tx_packets++;
>  		clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
> +		spin_unlock(&sl->lock);
>  		sl_unlock(sl);
>  		return;
>  	}
> @@ -441,6 +443,7 @@ static void slip_write_wakeup(struct tty_struct *tty)
>  	actual = tty->ops->write(tty, sl->xhead, sl->xleft);
>  	sl->xleft -= actual;
>  	sl->xhead += actual;
> +	spin_unlock(&sl->lock);
>  }
>  
>  static void sl_tx_timeout(struct net_device *dev)
>