Re: drivers/net/virtio_net.c:1227 xsk_append_merge_buffer() warn: unsigned '_x' is never less than zero.

[Xuan Zhuo <xuanzhuo@linux.alibaba.com>]

On Sun, 16 Feb 2025 11:13:14 +0800, kernel test robot <lkp@intel.com> wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   496659003dac5d08ea292c44fce9dfb36fa34691
> commit: 99c861b44eb1fb9dfe8776854116a6a9064c19bb virtio_net: xsk: rx: support recv merge mode
> date:   7 months ago
> config: riscv-randconfig-r073-20250213 (https://download.01.org/0day-ci/archive/20250216/202502161158.KmluxANz-lkp@intel.com/config)
> compiler: riscv32-linux-gcc (GCC) 14.2.0
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202502161158.KmluxANz-lkp@intel.com/
>
> New smatch warnings:
> drivers/net/virtio_net.c:1227 xsk_append_merge_buffer() warn: unsigned '_x' is never less than zero.

This seems to be in the mm system.

Thanks.


>
> Old smatch warnings:
> include/linux/mm.h:1311 virt_to_head_page() warn: unsigned '_x' is never less than zero.
> include/linux/scatterlist.h:189 sg_set_buf() warn: unsigned '_x' is never less than zero.
> drivers/net/virtio_net.c:1934 build_skb_from_xdp_buff() error: uninitialized symbol 'nr_frags'.
> drivers/net/virtio_net.c:2016 virtnet_build_xdp_buff_mrg() error: uninitialized symbol 'shinfo'.
> drivers/net/virtio_net.c:5096 virtnet_update_settings() error: uninitialized symbol 'virtio_cread_v'.
> drivers/net/virtio_net.c:5804 virtnet_config_changed_work() error: uninitialized symbol 'virtio_cread_v'.
> drivers/net/virtio_net.c:5808 virtnet_config_changed_work() error: uninitialized symbol 'v'.
>
> vim +/_x +1227 drivers/net/virtio_net.c
>
>   1184
>   1185	static int xsk_append_merge_buffer(struct virtnet_info *vi,
>   1186					   struct receive_queue *rq,
>   1187					   struct sk_buff *head_skb,
>   1188					   u32 num_buf,
>   1189					   struct virtio_net_hdr_mrg_rxbuf *hdr,
>   1190					   struct virtnet_rq_stats *stats)
>   1191	{
>   1192		struct sk_buff *curr_skb;
>   1193		struct xdp_buff *xdp;
>   1194		u32 len, truesize;
>   1195		struct page *page;
>   1196		void *buf;
>   1197
>   1198		curr_skb = head_skb;
>   1199
>   1200		while (--num_buf) {
>   1201			buf = virtqueue_get_buf(rq->vq, &len);
>   1202			if (unlikely(!buf)) {
>   1203				pr_debug("%s: rx error: %d buffers out of %d missing\n",
>   1204					 vi->dev->name, num_buf,
>   1205					 virtio16_to_cpu(vi->vdev,
>   1206							 hdr->num_buffers));
>   1207				DEV_STATS_INC(vi->dev, rx_length_errors);
>   1208				return -EINVAL;
>   1209			}
>   1210
>   1211			u64_stats_add(&stats->bytes, len);
>   1212
>   1213			xdp = buf_to_xdp(vi, rq, buf, len);
>   1214			if (!xdp)
>   1215				goto err;
>   1216
>   1217			buf = napi_alloc_frag(len);
>   1218			if (!buf) {
>   1219				xsk_buff_free(xdp);
>   1220				goto err;
>   1221			}
>   1222
>   1223			memcpy(buf, xdp->data - vi->hdr_len, len);
>   1224
>   1225			xsk_buff_free(xdp);
>   1226
> > 1227			page = virt_to_page(buf);
>   1228
>   1229			truesize = len;
>   1230
>   1231			curr_skb  = virtnet_skb_append_frag(head_skb, curr_skb, page,
>   1232							    buf, len, truesize);
>   1233			if (!curr_skb) {
>   1234				put_page(page);
>   1235				goto err;
>   1236			}
>   1237		}
>   1238
>   1239		return 0;
>   1240
>   1241	err:
>   1242		xsk_drop_follow_bufs(vi->dev, rq, num_buf, stats);
>   1243		return -EINVAL;
>   1244	}
>   1245
>
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki