net/mpc5200: Fix locking on fec_mpc52xx driver

Fix the locking scheme on the fec_mpc52xx driver.  This device can
receive IRQs from three sources; the FEC itself, the tx DMA, and the
rx DMA.  Mutual exclusion was handled by taking a spin_lock() in the
critical regions, but because the handlers are run with IRQs enabled,
spin_lock() is insufficient and the driver can end up interrupting
a critical region anyway from another IRQ.

Asier Llano discovered that this occurs when an error IRQ is raised
in the middle of handling rx irqs which resulted in an sk_buff memory
leak.

In addition, locking is spotty at best in the driver and inspection
revealed quite a few places with insufficient locking.

This patch is based on Asier's initial work, but reworks a number of
things so that locks are held for as short a time as possible, so
that spin_lock_irqsave() is used everywhere, and so the locks are
dropped when calling into the network stack (because the lock only
protects the hardware interface; not the network stack).

Boot tested on a lite5200 with an NFS root.  Has not been performance
tested.
Signed-off-by: NAsier Llano <a.llano@ziv.es>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/fec_mpc52xx.c

@@ -85,11 +85,15 @@ MODULE_PARM_DESC(debug, "debugging messages level");
 
 static void mpc52xx_fec_tx_timeout(struct net_device *dev)
 {
+	struct mpc52xx_fec_priv *priv = netdev_priv(dev);
+	unsigned long flags;
+
 	dev_warn(&dev->dev, "transmit timed out\n");
 
+	spin_lock_irqsave(&priv->lock, flags);
 	mpc52xx_fec_reset(dev);
-
 	dev->stats.tx_errors++;
+	spin_unlock_irqrestore(&priv->lock, flags);
 
 	netif_wake_queue(dev);
 }
@@ -135,28 +139,32 @@ static void mpc52xx_fec_free_rx_buffers(struct net_device *dev, struct bcom_task
 	}
 }
 
+static void
+mpc52xx_fec_rx_submit(struct net_device *dev, struct sk_buff *rskb)
+{
+	struct mpc52xx_fec_priv *priv = netdev_priv(dev);
+	struct bcom_fec_bd *bd;
+
+	bd = (struct bcom_fec_bd *) bcom_prepare_next_buffer(priv->rx_dmatsk);
+	bd->status = FEC_RX_BUFFER_SIZE;
+	bd->skb_pa = dma_map_single(dev->dev.parent, rskb->data,
+				    FEC_RX_BUFFER_SIZE, DMA_FROM_DEVICE);
+	bcom_submit_next_buffer(priv->rx_dmatsk, rskb);
+}
+
 static int mpc52xx_fec_alloc_rx_buffers(struct net_device *dev, struct bcom_task *rxtsk)
 {
-	while (!bcom_queue_full(rxtsk)) {
-		struct sk_buff *skb;
-		struct bcom_fec_bd *bd;
+	struct sk_buff *skb;
 
+	while (!bcom_queue_full(rxtsk)) {
 		skb = dev_alloc_skb(FEC_RX_BUFFER_SIZE);
-		if (skb == NULL)
+		if (!skb)
 			return -EAGAIN;
 
 		/* zero out the initial receive buffers to aid debugging */
 		memset(skb->data, 0, FEC_RX_BUFFER_SIZE);
-
-		bd = (struct bcom_fec_bd *)bcom_prepare_next_buffer(rxtsk);
-
-		bd->status = FEC_RX_BUFFER_SIZE;
-		bd->skb_pa = dma_map_single(dev->dev.parent, skb->data,
-				FEC_RX_BUFFER_SIZE, DMA_FROM_DEVICE);
-
-		bcom_submit_next_buffer(rxtsk, skb);
+		mpc52xx_fec_rx_submit(dev, skb);
 	}
-
 	return 0;
 }
 
@@ -328,13 +336,12 @@ static int mpc52xx_fec_start_xmit(struct sk_buff *skb, struct net_device *dev)
 				    DMA_TO_DEVICE);
 
 	bcom_submit_next_buffer(priv->tx_dmatsk, skb);
+	spin_unlock_irqrestore(&priv->lock, flags);
 
 	if (bcom_queue_full(priv->tx_dmatsk)) {
 		netif_stop_queue(dev);
 	}
 
-	spin_unlock_irqrestore(&priv->lock, flags);
-
 	return NETDEV_TX_OK;
 }
 
@@ -359,9 +366,9 @@ static irqreturn_t mpc52xx_fec_tx_interrupt(int irq, void *dev_id)
 {
 	struct net_device *dev = dev_id;
 	struct mpc52xx_fec_priv *priv = netdev_priv(dev);
+	unsigned long flags;
 
-	spin_lock(&priv->lock);
-
+	spin_lock_irqsave(&priv->lock, flags);
 	while (bcom_buffer_done(priv->tx_dmatsk)) {
 		struct sk_buff *skb;
 		struct bcom_fec_bd *bd;
@@ -372,11 +379,10 @@ static irqreturn_t mpc52xx_fec_tx_interrupt(int irq, void *dev_id)
 
 		dev_kfree_skb_irq(skb);
 	}
+	spin_unlock_irqrestore(&priv->lock, flags);
 
 	netif_wake_queue(dev);
 
-	spin_unlock(&priv->lock);
-
 	return IRQ_HANDLED;
 }
 
@@ -384,67 +390,60 @@ static irqreturn_t mpc52xx_fec_rx_interrupt(int irq, void *dev_id)
 {
 	struct net_device *dev = dev_id;
 	struct mpc52xx_fec_priv *priv = netdev_priv(dev);
+	struct sk_buff *rskb; /* received sk_buff */
+	struct sk_buff *skb;  /* new sk_buff to enqueue in its place */
+	struct bcom_fec_bd *bd;
+	u32 status, physaddr;
+	int length;
+	unsigned long flags;
+
+	spin_lock_irqsave(&priv->lock, flags);
 
 	while (bcom_buffer_done(priv->rx_dmatsk)) {
-		struct sk_buff *skb;
-		struct sk_buff *rskb;
-		struct bcom_fec_bd *bd;
-		u32 status;
 
 		rskb = bcom_retrieve_buffer(priv->rx_dmatsk, &status,
-				(struct bcom_bd **)&bd);
-		dma_unmap_single(dev->dev.parent, bd->skb_pa, rskb->len,
-				 DMA_FROM_DEVICE);
+					    (struct bcom_bd **)&bd);
+		physaddr = bd->skb_pa;
 
 		/* Test for errors in received frame */
 		if (status & BCOM_FEC_RX_BD_ERRORS) {
 			/* Drop packet and reuse the buffer */
-			bd = (struct bcom_fec_bd *)
-				bcom_prepare_next_buffer(priv->rx_dmatsk);
-
-			bd->status = FEC_RX_BUFFER_SIZE;
-			bd->skb_pa = dma_map_single(dev->dev.parent,
-					rskb->data,
-					FEC_RX_BUFFER_SIZE, DMA_FROM_DEVICE);
-
-			bcom_submit_next_buffer(priv->rx_dmatsk, rskb);
-
+			mpc52xx_fec_rx_submit(dev, rskb);
 			dev->stats.rx_dropped++;
-
 			continue;
 		}
 
 		/* skbs are allocated on open, so now we allocate a new one,
 		 * and remove the old (with the packet) */
 		skb = dev_alloc_skb(FEC_RX_BUFFER_SIZE);
-		if (skb) {
-			/* Process the received skb */
-			int length = status & BCOM_FEC_RX_BD_LEN_MASK;
-
-			skb_put(rskb, length - 4);	/* length without CRC32 */
-
-			rskb->dev = dev;
-			rskb->protocol = eth_type_trans(rskb, dev);
-
-			netif_rx(rskb);
-		} else {
+		if (!skb) {
 			/* Can't get a new one : reuse the same & drop pkt */
-			dev_notice(&dev->dev, "Memory squeeze, dropping packet.\n");
+			dev_notice(&dev->dev, "Low memory - dropped packet.\n");
+			mpc52xx_fec_rx_submit(dev, rskb);
 			dev->stats.rx_dropped++;
-
-			skb = rskb;
+			continue;
 		}
 
-		bd = (struct bcom_fec_bd *)
-			bcom_prepare_next_buffer(priv->rx_dmatsk);
+		/* Enqueue the new sk_buff back on the hardware */
+		mpc52xx_fec_rx_submit(dev, skb);
 
-		bd->status = FEC_RX_BUFFER_SIZE;
-		bd->skb_pa = dma_map_single(dev->dev.parent, skb->data,
-				FEC_RX_BUFFER_SIZE, DMA_FROM_DEVICE);
+		/* Process the received skb - Drop the spin lock while
+		 * calling into the network stack */
+		spin_unlock_irqrestore(&priv->lock, flags);
 
-		bcom_submit_next_buffer(priv->rx_dmatsk, skb);
+		dma_unmap_single(dev->dev.parent, physaddr, rskb->len,
+				 DMA_FROM_DEVICE);
+		length = status & BCOM_FEC_RX_BD_LEN_MASK;
+		skb_put(rskb, length - 4);	/* length without CRC32 */
+		rskb->dev = dev;
+		rskb->protocol = eth_type_trans(rskb, dev);
+		netif_rx(rskb);
+
+		spin_lock_irqsave(&priv->lock, flags);
 	}
 
+	spin_unlock_irqrestore(&priv->lock, flags);
+
 	return IRQ_HANDLED;
 }
 
@@ -454,6 +453,7 @@ static irqreturn_t mpc52xx_fec_interrupt(int irq, void *dev_id)
 	struct mpc52xx_fec_priv *priv = netdev_priv(dev);
 	struct mpc52xx_fec __iomem *fec = priv->fec;
 	u32 ievent;
+	unsigned long flags;
 
 	ievent = in_be32(&fec->ievent);
 
@@ -471,9 +471,10 @@ static irqreturn_t mpc52xx_fec_interrupt(int irq, void *dev_id)
 		if (net_ratelimit() && (ievent & FEC_IEVENT_XFIFO_ERROR))
 			dev_warn(&dev->dev, "FEC_IEVENT_XFIFO_ERROR\n");
 
+		spin_lock_irqsave(&priv->lock, flags);
 		mpc52xx_fec_reset(dev);
+		spin_unlock_irqrestore(&priv->lock, flags);
 
-		netif_wake_queue(dev);
 		return IRQ_HANDLED;
 	}
 
@@ -768,6 +769,8 @@ static void mpc52xx_fec_reset(struct net_device *dev)
 	bcom_enable(priv->tx_dmatsk);
 
 	mpc52xx_fec_start(dev);
+
+	netif_wake_queue(dev);
 }