[PATCH net] net: ethernet: mediatek: avoid potential invalid memory access

[kbuild test robot]

Hi Sean,

[auto build test WARNING on net/master]

url:    https://github.com/0day-ci/linux/commits/sean-wang-mediatek-com/net-ethernet-mediatek-avoid-potential-invalid-memory-access/20170722-155541
config: arm-allmodconfig (attached as .config)
compiler: arm-linux-gnueabi-gcc (Debian 6.1.1-9) 6.1.1 20160705
reproduce:
        wget https://raw.githubusercontent.com/01org/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=arm 

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

   drivers/net//ethernet/mediatek/mtk_eth_soc.c: In function 'mtk_napi_rx':
>> drivers/net//ethernet/mediatek/mtk_eth_soc.c:952:28: warning: 'netdev' may be used uninitialized in this function [-Wmaybe-uninitialized]
       netdev->stats.rx_dropped++;
       ~~~~~~~~~~~~~~~~~~~~~~~~^~
   drivers/net//ethernet/mediatek/mtk_eth_soc.c:928:22: note: 'netdev' was declared here
      struct net_device *netdev;
                         ^~~~~~

vim +/netdev +952 drivers/net//ethernet/mediatek/mtk_eth_soc.c

   916	
   917	static int mtk_poll_rx(struct napi_struct *napi, int budget,
   918			       struct mtk_eth *eth)
   919	{
   920		struct mtk_rx_ring *ring;
   921		int idx;
   922		struct sk_buff *skb;
   923		u8 *data, *new_data;
   924		struct mtk_rx_dma *rxd, trxd;
   925		int done = 0;
   926	
   927		while (done < budget) {
   928			struct net_device *netdev;
   929			unsigned int pktlen;
   930			dma_addr_t dma_addr;
   931			int mac = 0;
   932	
   933			ring = mtk_get_rx_ring(eth);
   934			if (unlikely(!ring))
   935				goto rx_done;
   936	
   937			idx = NEXT_RX_DESP_IDX(ring->calc_idx, ring->dma_size);
   938			rxd = &ring->dma[idx];
   939			data = ring->data[idx];
   940	
   941			mtk_rx_get_desc(&trxd, rxd);
   942			if (!(trxd.rxd2 & RX_DMA_DONE))
   943				break;
   944	
   945			/* find out which mac the packet come from. values start at 1 */
   946			mac = (trxd.rxd4 >> RX_DMA_FPORT_SHIFT) &
   947			      RX_DMA_FPORT_MASK;
   948			mac--;
   949	
   950			if (unlikely(mac < 0 || mac >= MTK_MAC_COUNT ||
   951				     !eth->netdev[mac])) {
 > 952				netdev->stats.rx_dropped++;
   953				goto release_desc;
   954			}
   955	
   956			netdev = eth->netdev[mac];
   957	
   958			if (unlikely(test_bit(MTK_RESETTING, &eth->state)))
   959				goto release_desc;
   960	
   961			/* alloc new buffer */
   962			new_data = napi_alloc_frag(ring->frag_size);
   963			if (unlikely(!new_data)) {
   964				netdev->stats.rx_dropped++;
   965				goto release_desc;
   966			}
   967			dma_addr = dma_map_single(eth->dev,
   968						  new_data + NET_SKB_PAD,
   969						  ring->buf_size,
   970						  DMA_FROM_DEVICE);
   971			if (unlikely(dma_mapping_error(eth->dev, dma_addr))) {
   972				skb_free_frag(new_data);
   973				netdev->stats.rx_dropped++;
   974				goto release_desc;
   975			}
   976	
   977			/* receive data */
   978			skb = build_skb(data, ring->frag_size);
   979			if (unlikely(!skb)) {
   980				skb_free_frag(new_data);
   981				netdev->stats.rx_dropped++;
   982				goto release_desc;
   983			}
   984			skb_reserve(skb, NET_SKB_PAD + NET_IP_ALIGN);
   985	
   986			dma_unmap_single(eth->dev, trxd.rxd1,
   987					 ring->buf_size, DMA_FROM_DEVICE);
   988			pktlen = RX_DMA_GET_PLEN0(trxd.rxd2);
   989			skb->dev = netdev;
   990			skb_put(skb, pktlen);
   991			if (trxd.rxd4 & RX_DMA_L4_VALID)
   992				skb->ip_summed = CHECKSUM_UNNECESSARY;
   993			else
   994				skb_checksum_none_assert(skb);
   995			skb->protocol = eth_type_trans(skb, netdev);
   996	
   997			if (netdev->features & NETIF_F_HW_VLAN_CTAG_RX &&
   998			    RX_DMA_VID(trxd.rxd3))
   999				__vlan_hwaccel_put_tag(skb, htons(ETH_P_8021Q),
  1000						       RX_DMA_VID(trxd.rxd3));
  1001			skb_record_rx_queue(skb, 0);
  1002			napi_gro_receive(napi, skb);
  1003	
  1004			ring->data[idx] = new_data;
  1005			rxd->rxd1 = (unsigned int)dma_addr;
  1006	
  1007	release_desc:
  1008			rxd->rxd2 = RX_DMA_PLEN0(ring->buf_size);
  1009	
  1010			ring->calc_idx = idx;
  1011	
  1012			done++;
  1013		}
  1014	
  1015	rx_done:
  1016		if (done) {
  1017			/* make sure that all changes to the dma ring are flushed before
  1018			 * we continue
  1019			 */
  1020			wmb();
  1021			mtk_update_rx_cpu_idx(eth);
  1022		}
  1023	
  1024		return done;
  1025	}
  1026	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
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