Hi chengjunjia, FYI, the error/warning still remains. tree: https://gitee.com/openeuler/kernel.git OLK-6.6 head: dc90c923fed4944f134644261022885c12631518 commit: abe6bde15def9470fe18af30626e62d51f651dd9 [2687/2687] net: tcp: Modify codes for better compatibility of code format config: x86_64-buildonly-randconfig-2002-20250818 (https://download.01.org/0day-ci/archive/20250818/202508181721.Nui6OZLt-lkp@i...) compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261) reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250818/202508181721.Nui6OZLt-lkp@i...) 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/202508181721.Nui6OZLt-lkp@intel.com/ All warnings (new ones prefixed by >>): In file included from net/ipv4/tcp_output.c:40: In file included from include/net/tcp.h:20: In file included from include/linux/tcp.h:17: In file included from include/linux/skbuff.h:17: In file included from include/linux/bvec.h:10: In file included from include/linux/highmem.h:8: In file included from include/linux/cacheflush.h:5: In file included from arch/x86/include/asm/cacheflush.h:5: In file included from include/linux/mm.h:2247: include/linux/vmstat.h:522:36: warning: arithmetic between different enumeration types ('enum node_stat_item' and 'enum lru_list') [-Wenum-enum-conversion] 522 | return node_stat_name(NR_LRU_BASE + lru) + 3; // skip "nr_" | ~~~~~~~~~~~ ^ ~~~ net/ipv4/tcp_output.c:186:3: warning: result of comparison of constant -1 with expression of type 'u8' (aka 'unsigned char') is always false [-Wtautological-constant-out-of-range-compare] 186 | NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED, | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 187 | tp->compressed_ack); | ~~~~~~~~~~~~~~~~~~~ include/net/ip.h:302:41: note: expanded from macro 'NET_ADD_STATS' 302 | #define NET_ADD_STATS(net, field, adnd) SNMP_ADD_STATS((net)->mib.net_statistics, field, adnd) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ include/net/snmp.h:143:4: note: expanded from macro 'SNMP_ADD_STATS' 143 | this_cpu_add(mib->mibs[field], addend) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ include/linux/percpu-defs.h:491:33: note: expanded from macro 'this_cpu_add' 491 | #define this_cpu_add(pcp, val) __pcpu_size_call(this_cpu_add_, pcp, val) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all) <scratch space>:64:1: note: expanded from here 64 | this_cpu_add_8 | ^ arch/x86/include/asm/percpu.h:370:35: note: expanded from macro 'this_cpu_add_8' 370 | #define this_cpu_add_8(pcp, val) percpu_add_op(8, volatile, (pcp), val) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ arch/x86/include/asm/percpu.h:127:31: note: expanded from macro 'percpu_add_op' 127 | ((val) == 1 || (val) == -1)) ? \ | ~~~~~ ^ ~~

...

net/ipv4/tcp_output.c:1312:5: warning: variable 'tcp_hdr_rsrvd_4b' set but not used [-Wunused-but-set-variable] 1312 | u8 tcp_hdr_rsrvd_4b; | ^ 3 warnings generated.

vim +/tcp_hdr_rsrvd_4b +1312 net/ipv4/tcp_output.c 1286 1287 /* This routine actually transmits TCP packets queued in by 1288 * tcp_do_sendmsg(). This is used by both the initial 1289 * transmission and possible later retransmissions. 1290 * All SKB's seen here are completely headerless. It is our 1291 * job to build the TCP header, and pass the packet down to 1292 * IP so it can do the same plus pass the packet off to the 1293 * device. 1294 * 1295 * We are working here with either a clone of the original 1296 * SKB, or a fresh unique copy made by the retransmit engine. 1297 */ 1298 static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, 1299 int clone_it, gfp_t gfp_mask, u32 rcv_nxt) 1300 { 1301 const struct inet_connection_sock *icsk = inet_csk(sk); 1302 struct inet_sock *inet; 1303 struct tcp_sock *tp; 1304 struct tcp_skb_cb *tcb; 1305 struct tcp_out_options opts; 1306 unsigned int tcp_options_size, tcp_header_size; 1307 struct sk_buff *oskb = NULL; 1308 struct tcp_md5sig_key *md5; 1309 struct tcphdr *th; 1310 u64 prior_wstamp; 1311 int err;

1312 u8 tcp_hdr_rsrvd_4b; 1313 1314 BUG_ON(!skb || !tcp_skb_pcount(skb)); 1315 tcp_hdr_rsrvd_4b = try_to_update_skb_for_caqm(sk, skb); 1316 tp = tcp_sk(sk); 1317 prior_wstamp = tp->tcp_wstamp_ns; 1318 tp->tcp_wstamp_ns = max(tp->tcp_wstamp_ns, tp->tcp_clock_cache); 1319 skb_set_delivery_time(skb, tp->tcp_wstamp_ns, true); 1320 if (clone_it) { 1321 oskb = skb; 1322 1323 tcp_skb_tsorted_save(oskb) { 1324 if (unlikely(skb_cloned(oskb))) 1325 skb = pskb_copy(oskb, gfp_mask); 1326 else 1327 skb = skb_clone(oskb, gfp_mask); 1328 } tcp_skb_tsorted_restore(oskb); 1329 1330 if (unlikely(!skb)) 1331 return -ENOBUFS; 1332 /* retransmit skbs might have a non zero value in skb->dev 1333 * because skb->dev is aliased with skb->rbnode.rb_left 1334 */ 1335 skb->dev = NULL; 1336 } 1337 1338 inet = inet_sk(sk); 1339 tcb = TCP_SKB_CB(skb); 1340 memset(&opts, 0, sizeof(opts)); 1341 1342 if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) { 1343 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5); 1344 } else { 1345 tcp_options_size = tcp_established_options(sk, skb, &opts, 1346 &md5); 1347 /* Force a PSH flag on all (GSO) packets to expedite GRO flush 1348 * at receiver : This slightly improve GRO performance. 1349 * Note that we do not force the PSH flag for non GSO packets, 1350 * because they might be sent under high congestion events, 1351 * and in this case it is better to delay the delivery of 1-MSS 1352 * packets and thus the corresponding ACK packet that would 1353 * release the following packet. 1354 */ 1355 if (tcp_skb_pcount(skb) > 1) 1356 tcb->tcp_flags |= TCPHDR_PSH; 1357 } 1358 tcp_header_size = tcp_options_size + sizeof(struct tcphdr); 1359 1360 /* We set skb->ooo_okay to one if this packet can select 1361 * a different TX queue than prior packets of this flow, 1362 * to avoid self inflicted reorders. 1363 * The 'other' queue decision is based on current cpu number 1364 * if XPS is enabled, or sk->sk_txhash otherwise. 1365 * We can switch to another (and better) queue if: 1366 * 1) No packet with payload is in qdisc/device queues. 1367 * Delays in TX completion can defeat the test 1368 * even if packets were already sent. 1369 * 2) Or rtx queue is empty. 1370 * This mitigates above case if ACK packets for 1371 * all prior packets were already processed. 1372 */ 1373 skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1) || 1374 tcp_rtx_queue_empty(sk); 1375 1376 /* If we had to use memory reserve to allocate this skb, 1377 * this might cause drops if packet is looped back : 1378 * Other socket might not have SOCK_MEMALLOC. 1379 * Packets not looped back do not care about pfmemalloc. 1380 */ 1381 skb->pfmemalloc = 0; 1382 1383 skb_push(skb, tcp_header_size); 1384 skb_reset_transport_header(skb); 1385 1386 skb_orphan(skb); 1387 skb->sk = sk; 1388 skb->destructor = skb_is_tcp_pure_ack(skb) ? __sock_wfree : tcp_wfree; 1389 refcount_add(skb->truesize, &sk->sk_wmem_alloc); 1390 1391 skb_set_dst_pending_confirm(skb, READ_ONCE(sk->sk_dst_pending_confirm)); 1392 1393 /* Build TCP header and checksum it. */ 1394 th = (struct tcphdr *)skb->data; 1395 th->source = inet->inet_sport; 1396 th->dest = inet->inet_dport; 1397 th->seq = htonl(tcb->seq); 1398 th->ack_seq = htonl(rcv_nxt); 1399 *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) | 1400 tcb->tcp_flags); 1401 #ifdef CONFIG_ETH_CAQM 1402 if (static_branch_unlikely(&sysctl_caqm_enable)) 1403 *(((__be16 *)th) + 6) |= htons((tcp_hdr_rsrvd_4b & 0x0F) << 8); 1404 #endif 1405 1406 th->check = 0; 1407 th->urg_ptr = 0; 1408 1409 /* The urg_mode check is necessary during a below snd_una win probe */ 1410 if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) { 1411 if (before(tp->snd_up, tcb->seq + 0x10000)) { 1412 th->urg_ptr = htons(tp->snd_up - tcb->seq); 1413 th->urg = 1; 1414 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) { 1415 th->urg_ptr = htons(0xFFFF); 1416 th->urg = 1; 1417 } 1418 } 1419 1420 skb_shinfo(skb)->gso_type = sk->sk_gso_type; 1421 if (likely(!(tcb->tcp_flags & TCPHDR_SYN))) { 1422 th->window = htons(tcp_select_window(sk)); 1423 tcp_ecn_send(sk, skb, th, tcp_header_size); 1424 } else { 1425 /* RFC1323: The window in SYN & SYN/ACK segments 1426 * is never scaled. 1427 */ 1428 th->window = htons(min(tp->rcv_wnd, 65535U)); 1429 } 1430 1431 tcp_options_write(th, tp, &opts); 1432

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