Subject: Re: [Kgdb-bugreport] [PATCH] 8139too: harden against TX ring overflow

From: Sergei Shtylyov <[email-masked]>
Date: Fri, 25 May 2007 01:29:29 +0400

Hello, I wrote:
> This driver's 4-packet deep TX queue is too sensible to the "careless" callers
> ignoring its state (like netpoll in trapped mode), so add "queue full" check at
> the start of the hard_start_xmit() method (only under #ifndef RTL8139_NDEBUG,
> otherwise the queue will get stuck once dirty pointer gets out of sync); switch
> to using appropriate mnemonics for the return values while at it.
> Also, the out-of-sync dirty pointer check is misplaced in rtl8139_tx_interrupt()
> which causes TX descriptors to be inspected more than once in case the pointer
> really gets out-of-sync (and incrementing the dirty pointer always by 4 is just
> not enough, e.g. KGDBoE managed to stuff 20+ extra buffers into the queue) --
> place it before the loop and limit the loop to only look through 4 descriptors
> at most, so that already overwritten descriptors are just not counted.

> Signed-off-by: Sergei Shtylyov <[email-masked]>

    Jeff, do you have any opinion on this patch?

> Index: linux-2.6/drivers/net/8139too.c
> ===================================================================
> --- linux-2.6.orig/drivers/net/8139too.c
> +++ linux-2.6/drivers/net/8139too.c
> @@ -90,7 +90,7 @@
>  */
>  
>  #define DRV_NAME	"8139too"
> -#define DRV_VERSION	"0.9.28"
> +#define DRV_VERSION	"0.9.31"
>  
>  
>  #include <linux/module.h>
> @@ -1708,6 +1708,13 @@ static int rtl8139_start_xmit (struct sk
>  	unsigned int len = skb->len;
>  	unsigned long flags;
>  
> +#ifndef RTL8139_NDEBUG
> +	if (unlikely((tp->cur_tx - tp->dirty_tx) >= NUM_TX_DESC)) {
> +		printk(KERN_ERR "%s: TX queue full!\n", dev->name);
> +		return NETDEV_TX_BUSY;
> +	}
> +#endif
> +
>  	/* Calculate the next Tx descriptor entry. */
>  	entry = tp->cur_tx % NUM_TX_DESC;
>  
> @@ -1720,7 +1727,7 @@ static int rtl8139_start_xmit (struct sk
>  	} else {
>  		dev_kfree_skb(skb);
>  		tp->stats.tx_dropped++;
> -		return 0;
> +		return NETDEV_TX_OK;
>  	}
>  
>  	spin_lock_irqsave(&tp->lock, flags);
> @@ -1740,7 +1747,7 @@ static int rtl8139_start_xmit (struct sk
>  		printk (KERN_DEBUG "%s: Queued Tx packet size %u to slot %d.\n",
>  			dev->name, len, entry);
>  
> -	return 0;
> +	return NETDEV_TX_OK;
>  }
>  
>  
> @@ -1755,6 +1762,16 @@ static void rtl8139_tx_interrupt (struct
>  
>  	dirty_tx = tp->dirty_tx;
>  	tx_left = tp->cur_tx - dirty_tx;
> +
> +#ifndef RTL8139_NDEBUG
> +	if (unlikely(tx_left > NUM_TX_DESC)) {
> +		printk(KERN_ERR "%s: Out-of-sync dirty pointer, %ld vs. %ld.\n",
> +		       dev->name, dirty_tx, tp->cur_tx);
> +		tx_left  = NUM_TX_DESC;
> +		dirty_tx = tp->cur_tx - NUM_TX_DESC;
> +	}
> +#endif /* RTL8139_NDEBUG */
> +
>  	while (tx_left > 0) {
>  		int entry = dirty_tx % NUM_TX_DESC;
>  		int txstatus;
> @@ -1797,14 +1814,6 @@ static void rtl8139_tx_interrupt (struct
>  		tx_left--;
>  	}
>  
> -#ifndef RTL8139_NDEBUG
> -	if (tp->cur_tx - dirty_tx > NUM_TX_DESC) {
> -		printk (KERN_ERR "%s: Out-of-sync dirty pointer, %ld vs. %ld.\n",
> -		        dev->name, dirty_tx, tp->cur_tx);
> -		dirty_tx += NUM_TX_DESC;
> -	}
> -#endif /* RTL8139_NDEBUG */
> -
>  	/* only wake the queue if we did work, and the queue is stopped */
>  	if (tp->dirty_tx != dirty_tx) {
>  		tp->dirty_tx = dirty_tx;
> 

WBR, Sergei