Re: [PATCH net-next 7/8] virtio_net: introduce receive_mergeable_xdp()

[kernel test robot <lkp@intel.com>]

Hi Xuan,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on net-next/main]

url:    https://github.com/intel-lab-lkp/linux/commits/Xuan-Zhuo/virtio_net-mergeable-xdp-put-old-page-immediately/20230322-110445
patch link:    https://lore.kernel.org/r/20230322030308.16046-8-xuanzhuo%40linux.alibaba.com
patch subject: [PATCH net-next 7/8] virtio_net: introduce receive_mergeable_xdp()
config: i386-randconfig-a002 (https://download.01.org/0day-ci/archive/20230323/202303230720.XUavHilr-lkp@intel.com/config)
compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project f28c006a5895fc0e329fe15fead81e37457cb1d1)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/c00edb888e239eb9eb468c0e93419f373f5e72a7
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Xuan-Zhuo/virtio_net-mergeable-xdp-put-old-page-immediately/20230322-110445
        git checkout c00edb888e239eb9eb468c0e93419f373f5e72a7
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=i386 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=i386 SHELL=/bin/bash drivers/net/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
| Link: https://lore.kernel.org/oe-kbuild-all/202303230720.XUavHilr-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> drivers/net/virtio_net.c:1399:6: warning: variable 'page' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
           if (unlikely(len > truesize - room)) {
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/compiler.h:78:22: note: expanded from macro 'unlikely'
   # define unlikely(x)    __builtin_expect(!!(x), 0)
                           ^~~~~~~~~~~~~~~~~~~~~~~~~~
   drivers/net/virtio_net.c:1490:11: note: uninitialized use occurs here
           put_page(page);
                    ^~~~
   drivers/net/virtio_net.c:1399:2: note: remove the 'if' if its condition is always false
           if (unlikely(len > truesize - room)) {
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   drivers/net/virtio_net.c:1392:19: note: initialize the variable 'page' to silence this warning
           struct page *page;
                            ^
                             = NULL
>> drivers/net/virtio_net.c:1399:6: warning: variable 'num_buf' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
           if (unlikely(len > truesize - room)) {
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/compiler.h:78:22: note: expanded from macro 'unlikely'
   # define unlikely(x)    __builtin_expect(!!(x), 0)
                           ^~~~~~~~~~~~~~~~~~~~~~~~~~
   drivers/net/virtio_net.c:1491:25: note: uninitialized use occurs here
           mergeable_buf_free(rq, num_buf, dev, stats);
                                  ^~~~~~~
   drivers/net/virtio_net.c:1399:2: note: remove the 'if' if its condition is always false
           if (unlikely(len > truesize - room)) {
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   drivers/net/virtio_net.c:1393:13: note: initialize the variable 'num_buf' to silence this warning
           int num_buf;
                      ^
                       = 0
   2 warnings generated.


vim +1399 drivers/net/virtio_net.c

  1375	
  1376	static struct sk_buff *receive_mergeable(struct net_device *dev,
  1377						 struct virtnet_info *vi,
  1378						 struct receive_queue *rq,
  1379						 void *buf,
  1380						 void *ctx,
  1381						 unsigned int len,
  1382						 unsigned int *xdp_xmit,
  1383						 struct virtnet_rq_stats *stats)
  1384	{
  1385		unsigned int truesize = mergeable_ctx_to_truesize(ctx);
  1386		unsigned int headroom = mergeable_ctx_to_headroom(ctx);
  1387		unsigned int tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
  1388		unsigned int room = SKB_DATA_ALIGN(headroom + tailroom);
  1389		struct virtio_net_hdr_mrg_rxbuf *hdr;
  1390		struct sk_buff *head_skb, *curr_skb;
  1391		struct bpf_prog *xdp_prog;
  1392		struct page *page;
  1393		int num_buf;
  1394		int offset;
  1395	
  1396		head_skb = NULL;
  1397		stats->bytes += len - vi->hdr_len;
  1398	
> 1399		if (unlikely(len > truesize - room)) {
  1400			pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
  1401				 dev->name, len, (unsigned long)(truesize - room));
  1402			dev->stats.rx_length_errors++;
  1403			goto err_skb;
  1404		}
  1405	
  1406		if (likely(vi->xdp_enabled)) {
  1407			rcu_read_lock();
  1408			xdp_prog = rcu_dereference(rq->xdp_prog);
  1409			if (xdp_prog) {
  1410				head_skb = receive_mergeable_xdp(dev, vi, rq, xdp_prog,
  1411								 buf, ctx, len, xdp_xmit,
  1412								 stats);
  1413				rcu_read_unlock();
  1414				return head_skb;
  1415			}
  1416			rcu_read_unlock();
  1417		}
  1418	
  1419		hdr = buf;
  1420		num_buf = virtio16_to_cpu(vi->vdev, hdr->num_buffers);
  1421		page = virt_to_head_page(buf);
  1422		offset = buf - page_address(page);
  1423	
  1424		head_skb = page_to_skb(vi, rq, page, offset, len, truesize, headroom);
  1425		curr_skb = head_skb;
  1426	
  1427		if (unlikely(!curr_skb))
  1428			goto err_skb;
  1429		while (--num_buf) {
  1430			int num_skb_frags;
  1431	
  1432			buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx);
  1433			if (unlikely(!buf)) {
  1434				pr_debug("%s: rx error: %d buffers out of %d missing\n",
  1435					 dev->name, num_buf,
  1436					 virtio16_to_cpu(vi->vdev,
  1437							 hdr->num_buffers));
  1438				dev->stats.rx_length_errors++;
  1439				goto err_buf;
  1440			}
  1441	
  1442			stats->bytes += len;
  1443			page = virt_to_head_page(buf);
  1444	
  1445			truesize = mergeable_ctx_to_truesize(ctx);
  1446			headroom = mergeable_ctx_to_headroom(ctx);
  1447			tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
  1448			room = SKB_DATA_ALIGN(headroom + tailroom);
  1449			if (unlikely(len > truesize - room)) {
  1450				pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
  1451					 dev->name, len, (unsigned long)(truesize - room));
  1452				dev->stats.rx_length_errors++;
  1453				goto err_skb;
  1454			}
  1455	
  1456			num_skb_frags = skb_shinfo(curr_skb)->nr_frags;
  1457			if (unlikely(num_skb_frags == MAX_SKB_FRAGS)) {
  1458				struct sk_buff *nskb = alloc_skb(0, GFP_ATOMIC);
  1459	
  1460				if (unlikely(!nskb))
  1461					goto err_skb;
  1462				if (curr_skb == head_skb)
  1463					skb_shinfo(curr_skb)->frag_list = nskb;
  1464				else
  1465					curr_skb->next = nskb;
  1466				curr_skb = nskb;
  1467				head_skb->truesize += nskb->truesize;
  1468				num_skb_frags = 0;
  1469			}
  1470			if (curr_skb != head_skb) {
  1471				head_skb->data_len += len;
  1472				head_skb->len += len;
  1473				head_skb->truesize += truesize;
  1474			}
  1475			offset = buf - page_address(page);
  1476			if (skb_can_coalesce(curr_skb, num_skb_frags, page, offset)) {
  1477				put_page(page);
  1478				skb_coalesce_rx_frag(curr_skb, num_skb_frags - 1,
  1479						     len, truesize);
  1480			} else {
  1481				skb_add_rx_frag(curr_skb, num_skb_frags, page,
  1482						offset, len, truesize);
  1483			}
  1484		}
  1485	
  1486		ewma_pkt_len_add(&rq->mrg_avg_pkt_len, head_skb->len);
  1487		return head_skb;
  1488	
  1489	err_skb:
  1490		put_page(page);
  1491		mergeable_buf_free(rq, num_buf, dev, stats);
  1492	
  1493	err_buf:
  1494		stats->drops++;
  1495		dev_kfree_skb(head_skb);
  1496		return NULL;
  1497	}
  1498	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests