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: Asier Llano <a.llano@ziv.es>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 62 insertions, 59 deletions

diff --git a/drivers/net/fec_mpc52xx.c b/drivers/net/fec_mpc52xx.c
index 6407672b28e9..848e8407ea8f 100644
--- a/drivers/net/fec_mpc52xx.c
+++ b/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);
 }