atm: eni: avoid accessing the data mapped to streaming DMA

In do_tx(), skb->data is mapped to streaming DMA on line 1111:
  paddr = dma_map_single(...,skb->data,DMA_TO_DEVICE);

Then skb->data is accessed on line 1153:
  (skb->data[3] & 0xf)

This access may cause data inconsistency between CPU cache and hardware.

To fix this problem, skb->data[3] is assigned to a local variable before
DMA mapping, and then the driver accesses this local variable instead of
skb->data[3].
Signed-off-by: Jia-Ju Bai <baijiaju@tsinghua.edu.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/atm/eni.c

@@ -1034,6 +1034,7 @@ static enum enq_res do_tx(struct sk_buff *skb)
 	u32 dma_rd,dma_wr;
 	u32 size; /* in words */
 	int aal5,dma_size,i,j;
+	unsigned char skb_data3;
 
 	DPRINTK(">do_tx\n");
 	NULLCHECK(skb);
@@ -1108,6 +1109,7 @@ DPRINTK("iovcnt = %d\n",skb_shinfo(skb)->nr_frags);
 		    vcc->dev->number);
 		return enq_jam;
 	}
+	skb_data3 = skb->data[3];
 	paddr = dma_map_single(&eni_dev->pci_dev->dev,skb->data,skb->len,
 			       DMA_TO_DEVICE);
 	ENI_PRV_PADDR(skb) = paddr;
@@ -1150,7 +1152,7 @@ DPRINTK("doing direct send\n"); /* @@@ well, this doesn't work anyway */
 	    (size/(ATM_CELL_PAYLOAD/4)),tx->send+tx->tx_pos*4);
 /*printk("dsc = 0x%08lx\n",(unsigned long) readl(tx->send+tx->tx_pos*4));*/
 	writel((vcc->vci << MID_SEG_VCI_SHIFT) |
-            (aal5 ? 0 : (skb->data[3] & 0xf)) |
+            (aal5 ? 0 : (skb_data3 & 0xf)) |
 	    (ATM_SKB(skb)->atm_options & ATM_ATMOPT_CLP ? MID_SEG_CLP : 0),
 	    tx->send+((tx->tx_pos+1) & (tx->words-1))*4);
 	DPRINTK("size: %d, len:%d\n",size,skb->len);