Re: [PATCH net-next v4 2/2] net: devmem: use niov array for token management

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

Hi Bobby,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 203e3beb73e53584ca90bc2a6d8240b9b12b9bcf]

url:    https://github.com/intel-lab-lkp/linux/commits/Bobby-Eshleman/net-devmem-rename-tx_vec-to-vec-in-dmabuf-binding/20250927-003521
base:   203e3beb73e53584ca90bc2a6d8240b9b12b9bcf
patch link:    https://lore.kernel.org/r/20250926-scratch-bobbyeshleman-devmem-tcp-token-upstream-v4-2-39156563c3ea%40meta.com
patch subject: [PATCH net-next v4 2/2] net: devmem: use niov array for token management
config: x86_64-buildonly-randconfig-005-20250927 (https://download.01.org/0day-ci/archive/20250927/202509271623.I36w4Uqo-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250927/202509271623.I36w4Uqo-lkp@intel.com/reproduce)

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/202509271623.I36w4Uqo-lkp@intel.com/

All warnings (new ones prefixed by >>):

   net/ipv4/tcp.c: In function 'tcp_recvmsg_dmabuf':
>> net/ipv4/tcp.c:2473:32: warning: unused variable 'len' [-Wunused-variable]
    2473 |                         size_t len;
         |                                ^~~
>> net/ipv4/tcp.c:2472:32: warning: unused variable 'size' [-Wunused-variable]
    2472 |                         size_t size;
         |                                ^~~~


vim +/len +2473 net/ipv4/tcp.c

  2409	
  2410	/* On error, returns the -errno. On success, returns number of bytes sent to the
  2411	 * user. May not consume all of @remaining_len.
  2412	 */
  2413	static int tcp_recvmsg_dmabuf(struct sock *sk, const struct sk_buff *skb,
  2414				      unsigned int offset, struct msghdr *msg,
  2415				      int remaining_len)
  2416	{
  2417		struct dmabuf_cmsg dmabuf_cmsg = { 0 };
  2418		unsigned int start;
  2419		int i, copy, n;
  2420		int sent = 0;
  2421		int err = 0;
  2422	
  2423		do {
  2424			start = skb_headlen(skb);
  2425	
  2426			if (skb_frags_readable(skb)) {
  2427				err = -ENODEV;
  2428				goto out;
  2429			}
  2430	
  2431			/* Copy header. */
  2432			copy = start - offset;
  2433			if (copy > 0) {
  2434				copy = min(copy, remaining_len);
  2435	
  2436				n = copy_to_iter(skb->data + offset, copy,
  2437						 &msg->msg_iter);
  2438				if (n != copy) {
  2439					err = -EFAULT;
  2440					goto out;
  2441				}
  2442	
  2443				offset += copy;
  2444				remaining_len -= copy;
  2445	
  2446				/* First a dmabuf_cmsg for # bytes copied to user
  2447				 * buffer.
  2448				 */
  2449				memset(&dmabuf_cmsg, 0, sizeof(dmabuf_cmsg));
  2450				dmabuf_cmsg.frag_size = copy;
  2451				err = put_cmsg_notrunc(msg, SOL_SOCKET,
  2452						       SO_DEVMEM_LINEAR,
  2453						       sizeof(dmabuf_cmsg),
  2454						       &dmabuf_cmsg);
  2455				if (err)
  2456					goto out;
  2457	
  2458				sent += copy;
  2459	
  2460				if (remaining_len == 0)
  2461					goto out;
  2462			}
  2463	
  2464			/* after that, send information of dmabuf pages through a
  2465			 * sequence of cmsg
  2466			 */
  2467			for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
  2468				skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
  2469				struct net_devmem_dmabuf_binding *binding;
  2470				struct net_iov *niov;
  2471				u64 frag_offset;
> 2472				size_t size;
> 2473				size_t len;
  2474				u32 token;
  2475				int end;
  2476	
  2477				/* !skb_frags_readable() should indicate that ALL the
  2478				 * frags in this skb are dmabuf net_iovs. We're checking
  2479				 * for that flag above, but also check individual frags
  2480				 * here. If the tcp stack is not setting
  2481				 * skb_frags_readable() correctly, we still don't want
  2482				 * to crash here.
  2483				 */
  2484				if (!skb_frag_net_iov(frag)) {
  2485					net_err_ratelimited("Found non-dmabuf skb with net_iov");
  2486					err = -ENODEV;
  2487					goto out;
  2488				}
  2489	
  2490				niov = skb_frag_net_iov(frag);
  2491				if (!net_is_devmem_iov(niov)) {
  2492					err = -ENODEV;
  2493					goto out;
  2494				}
  2495	
  2496				end = start + skb_frag_size(frag);
  2497				copy = end - offset;
  2498	
  2499				if (copy > 0) {
  2500					copy = min(copy, remaining_len);
  2501	
  2502					frag_offset = net_iov_virtual_addr(niov) +
  2503						      skb_frag_off(frag) + offset -
  2504						      start;
  2505					dmabuf_cmsg.frag_offset = frag_offset;
  2506					dmabuf_cmsg.frag_size = copy;
  2507	
  2508					binding = net_devmem_iov_binding(niov);
  2509	
  2510					if (!sk->sk_devmem_binding)
  2511						sk->sk_devmem_binding = binding;
  2512	
  2513					if (sk->sk_devmem_binding != binding) {
  2514						err = -EFAULT;
  2515						goto out;
  2516					}
  2517	
  2518					token = net_iov_virtual_addr(niov) >> PAGE_SHIFT;
  2519					dmabuf_cmsg.frag_token = token;
  2520	
  2521					/* Will perform the exchange later */
  2522					dmabuf_cmsg.dmabuf_id = net_devmem_iov_binding_id(niov);
  2523	
  2524					offset += copy;
  2525					remaining_len -= copy;
  2526	
  2527					err = put_cmsg_notrunc(msg, SOL_SOCKET,
  2528							       SO_DEVMEM_DMABUF,
  2529							       sizeof(dmabuf_cmsg),
  2530							       &dmabuf_cmsg);
  2531					if (err)
  2532						goto out;
  2533	
  2534					if (atomic_inc_return(&niov->uref) == 1)
  2535						atomic_long_inc(&niov->pp_ref_count);
  2536	
  2537					sent += copy;
  2538	
  2539					if (remaining_len == 0)
  2540						goto out;
  2541				}
  2542				start = end;
  2543			}
  2544	
  2545			if (!remaining_len)
  2546				goto out;
  2547	
  2548			/* if remaining_len is not satisfied yet, we need to go to the
  2549			 * next frag in the frag_list to satisfy remaining_len.
  2550			 */
  2551			skb = skb_shinfo(skb)->frag_list ?: skb->next;
  2552	
  2553			offset = offset - start;
  2554		} while (skb);
  2555	
  2556		if (remaining_len) {
  2557			err = -EFAULT;
  2558			goto out;
  2559		}
  2560	
  2561	out:
  2562		if (!sent)
  2563			sent = err;
  2564	
  2565		return sent;
  2566	}
  2567	

-- 
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https://github.com/intel/lkp-tests/wiki