Subject: Re: [PATCH] sis900: come alive after temporary memory shortage

From: Vasily Averin <[email-masked]>
Date: Sat, 08 Oct 2005 17:09:30 +0400

Daniele Venzano wrote:
> This patch is good and fixes some corner cases. Please consider for
> inclusion.

Daniele,
sorry, but unfortunately our patch was wrong.

> +	int rx_work_limit =
> +		(sis_priv->dirty_rx - sis_priv->cur_rx) % NUM_RX_DESC;

when dirty_rx = cur_rx it computes limit=0, but should be NUM_RX_DESC

Also I've noticed that 'if (sis_priv->rx_skbuff[entry] == NULL)' statement
inside the while loop is really impossible now. Therefore I've increased message
loglevel up to KERN_WARNING and added some useful debug.

Daniele, could you please check our new patch carefully?

Andrew, could you please drop our old patch and replace it by the new one?

Thank you,
	Vasily Averin, SWsoft Linux kernel team

Patch solves following problems:
1) Forgotten counter incrementation in sis900_rx() in case
     it doesn't get memory for skb, that leads to whole interface failure.
     Problem is accompanied with messages:
    eth0: Memory squeeze,deferring packet.
    eth0: NULL pointer encountered in Rx ring, skipping
2) If counter cur_rx overflows and there'll be temporary memory problems
     buffer can't be recreated later, when memory IS available.
3) Limit the work in handler to prevent the endless packets processing if
     new packets are generated faster then handled.

Signed-off-by: Konstantin Khorenko <[email-masked]>
Signed-off-by: Vasily Averin <[email-masked]>
--- a/drivers/net/sis900.c	2005-10-08 12:22:53.000000000 +0400
+++ b/drivers/net/sis900.c	2005-10-08 15:12:29.000000000 +0400
@@ -1696,15 +1696,20 @@ static int sis900_rx(struct net_device *
 	long ioaddr = net_dev->base_addr;
 	unsigned int entry = sis_priv->cur_rx % NUM_RX_DESC;
 	u32 rx_status = sis_priv->rx_ring[entry].cmdsts;
+	int rx_work_limit;
 
 	if (netif_msg_rx_status(sis_priv))
 		printk(KERN_DEBUG "sis900_rx, cur_rx:%4.4d, dirty_rx:%4.4d "
 		       "status:0x%8.8x\n",
 		       sis_priv->cur_rx, sis_priv->dirty_rx, rx_status);
+	rx_work_limit = sis_priv->dirty_rx + NUM_RX_DESC - sis_priv->cur_rx;
 
 	while (rx_status & OWN) {
 		unsigned int rx_size;
 
+		if (--rx_work_limit < 0)
+			break;
+
 		rx_size = (rx_status & DSIZE) - CRC_SIZE;
 
 		if (rx_status & (ABORT|OVERRUN|TOOLONG|RUNT|RXISERR|CRCERR|FAERR)) {
@@ -1732,9 +1737,11 @@ static int sis900_rx(struct net_device *
 			   we are working on NULL sk_buff :-( */
 			if (sis_priv->rx_skbuff[entry] == NULL) {
 				if (netif_msg_rx_err(sis_priv))
-					printk(KERN_INFO "%s: NULL pointer " 
-						"encountered in Rx ring, skipping\n",
-						net_dev->name);
+					printk(KERN_WARNING "%s: NULL pointer " 
+					      "encountered in Rx ring\n"
+					      "cur_rx:%4.4d, dirty_rx:%4.4d\n",
+					      net_dev->name, sis_priv->cur_rx,
+					      sis_priv->dirty_rx);
 				break;
 			}
 
@@ -1770,6 +1777,7 @@ static int sis900_rx(struct net_device *
 				sis_priv->rx_ring[entry].cmdsts = 0;
 				sis_priv->rx_ring[entry].bufptr = 0;
 				sis_priv->stats.rx_dropped++;
+				sis_priv->cur_rx++;
 				break;
 			}
 			skb->dev = net_dev;
@@ -1787,7 +1795,7 @@ static int sis900_rx(struct net_device *
 
 	/* refill the Rx buffer, what if the rate of refilling is slower
 	 * than consuming ?? */
-	for (;sis_priv->cur_rx - sis_priv->dirty_rx > 0; sis_priv->dirty_rx++) {
+	for (; sis_priv->cur_rx != sis_priv->dirty_rx; sis_priv->dirty_rx++) {
 		struct sk_buff *skb;
 
 		entry = sis_priv->dirty_rx % NUM_RX_DESC;