tree: https://github.com/dsahern/linux nexthops/del-group-03 head: b8c06bc47e0a04603de20861b8d5f7291ff0bc12 commit: 063512a047f24cd25298dbb37ae1247a407dbdde [4/7] ipv4: Refactor nhc evaluation in fib_table_lookup config: x86_64-allyesconfig (attached as .config) compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project 3393cc4cebf9969db94dc424b7a2b6195589c33b) 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 # install x86_64 cross compiling tool for clang build # apt-get install binutils-x86-64-linux-gnu git checkout 063512a047f24cd25298dbb37ae1247a407dbdde # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64 If you fix the issue, kindly add following tag as appropriate Reported-by: kbuild test robot <lkp(a)intel.com&gt; All warnings (new ones prefixed by >>, old ones prefixed by <<): if (nhc) ^~~ net/ipv4/fib_trie.c:1575:18: note: uninitialized use occurs here res->nh_sel = nhsel; ^~~~~ net/ipv4/fib_trie.c:1559:4: note: remove the 'if' if its condition is always false if (nhc) ^~~~~~~~ net/ipv4/fib_trie.c:1527:12: note: initialize the variable 'nhsel' to silence this warning int nhsel, err; ^ = 0 1 warning generated. vim +1559 net/ipv4/fib_trie.c 1420 1421 /* Step 1: Travel to the longest prefix match in the trie */ 1422 for (;;) { 1423 index = get_cindex(key, n); 1424 1425 /* This bit of code is a bit tricky but it combines multiple 1426 * checks into a single check. The prefix consists of the 1427 * prefix plus zeros for the "bits" in the prefix. The index 1428 * is the difference between the key and this value. From 1429 * this we can actually derive several pieces of data. 1430 * if (index >= (1ul << bits)) 1431 * we have a mismatch in skip bits and failed 1432 * else 1433 * we know the value is cindex 1434 * 1435 * This check is safe even if bits == KEYLENGTH due to the 1436 * fact that we can only allocate a node with 32 bits if a 1437 * long is greater than 32 bits. 1438 */ 1439 if (index >= (1ul << n->bits)) 1440 break; 1441 1442 /* we have found a leaf. Prefixes have already been compared */ 1443 if (IS_LEAF(n)) 1444 goto found; 1445 1446 /* only record pn and cindex if we are going to be chopping 1447 * bits later. Otherwise we are just wasting cycles. 1448 */ 1449 if (n->slen > n->pos) { 1450 pn = n; 1451 cindex = index; 1452 } 1453 1454 n = get_child_rcu(n, index); 1455 if (unlikely(!n)) 1456 goto backtrace; 1457 } 1458 1459 /* Step 2: Sort out leaves and begin backtracing for longest prefix */ 1460 for (;;) { 1461 /* record the pointer where our next node pointer is stored */ 1462 struct key_vector __rcu **cptr = n->tnode; 1463 1464 /* This test verifies that none of the bits that differ 1465 * between the key and the prefix exist in the region of 1466 * the lsb and higher in the prefix. 1467 */ 1468 if (unlikely(prefix_mismatch(key, n)) || (n->slen == n->pos)) 1469 goto backtrace; 1470 1471 /* exit out and process leaf */ 1472 if (unlikely(IS_LEAF(n))) 1473 break; 1474 1475 /* Don't bother recording parent info. Since we are in 1476 * prefix match mode we will have to come back to wherever 1477 * we started this traversal anyway 1478 */ 1479 1480 while ((n = rcu_dereference(*cptr)) == NULL) { 1481 backtrace: 1482 #ifdef CONFIG_IP_FIB_TRIE_STATS 1483 if (!n) 1484 this_cpu_inc(stats->null_node_hit); 1485 #endif 1486 /* If we are at cindex 0 there are no more bits for 1487 * us to strip at this level so we must ascend back 1488 * up one level to see if there are any more bits to 1489 * be stripped there. 1490 */ 1491 while (!cindex) { 1492 t_key pkey = pn->key; 1493 1494 /* If we don't have a parent then there is 1495 * nothing for us to do as we do not have any 1496 * further nodes to parse. 1497 */ 1498 if (IS_TRIE(pn)) { 1499 trace_fib_table_lookup(tb->tb_id, flp, 1500 NULL, -EAGAIN); 1501 return -EAGAIN; 1502 } 1503 #ifdef CONFIG_IP_FIB_TRIE_STATS 1504 this_cpu_inc(stats->backtrack); 1505 #endif 1506 /* Get Child's index */ 1507 pn = node_parent_rcu(pn); 1508 cindex = get_index(pkey, pn); 1509 } 1510 1511 /* strip the least significant bit from the cindex */ 1512 cindex &= cindex - 1; 1513 1514 /* grab pointer for next child node */ 1515 cptr = &pn->tnode[cindex]; 1516 } 1517 } 1518 1519 found: 1520 /* this line carries forward the xor from earlier in the function */ 1521 index = key ^ n->key; 1522 1523 /* Step 3: Process the leaf, if that fails fall back to backtracing */ 1524 hlist_for_each_entry_rcu(fa, &n->leaf, fa_list) { 1525 struct fib_info *fi = fa->fa_info; 1526 struct fib_nh_common *nhc; 1527 int nhsel, err; 1528 1529 if ((BITS_PER_LONG > KEYLENGTH) || (fa->fa_slen < KEYLENGTH)) { 1530 if (index >= (1ul << fa->fa_slen)) 1531 continue; 1532 } 1533 if (fa->fa_tos && fa->fa_tos != flp->flowi4_tos) 1534 continue; 1535 if (fi->fib_dead) 1536 continue; 1537 if (fa->fa_info->fib_scope < flp->flowi4_scope) 1538 continue; 1539 fib_alias_accessed(fa); 1540 err = fib_props[fa->fa_type].error; 1541 if (unlikely(err < 0)) { 1542 out_reject: 1543 #ifdef CONFIG_IP_FIB_TRIE_STATS 1544 this_cpu_inc(stats->semantic_match_passed); 1545 #endif 1546 trace_fib_table_lookup(tb->tb_id, flp, NULL, err); 1547 return err; 1548 } 1549 if (fi->fib_flags & RTNH_F_DEAD) 1550 continue; 1551 1552 if (unlikely(fi->nh)) { 1553 if (nexthop_is_blackhole(fi->nh)) { 1554 err = fib_props[RTN_BLACKHOLE].error; 1555 goto out_reject; 1556 } 1557 1558 nhc = nexthop_get_nhc_lookup(fi->nh, fib_flags, flp); 1560 goto set_result; 1561 goto miss; 1562 } 1563 1564 for (nhsel = 0; nhsel < fib_info_num_path(fi); nhsel++) { 1565 nhc = fib_info_nhc(fi, nhsel); 1566 1567 if (!fib_lookup_good_nhc(nhc, fib_flags, flp)) 1568 continue; 1569 set_result: 1570 if (!(fib_flags & FIB_LOOKUP_NOREF)) 1571 refcount_inc(&fi->fib_clntref); 1572 1573 res->prefix = htonl(n->key); 1574 res->prefixlen = KEYLENGTH - fa->fa_slen; 1575 res->nh_sel = nhsel; 1576 res->nhc = nhc; 1577 res->type = fa->fa_type; 1578 res->scope = fi->fib_scope; 1579 res->fi = fi; 1580 res->table = tb; 1581 res->fa_head = &n->leaf; 1582 #ifdef CONFIG_IP_FIB_TRIE_STATS 1583 this_cpu_inc(stats->semantic_match_passed); 1584 #endif 1585 trace_fib_table_lookup(tb->tb_id, flp, nhc, err); 1586 1587 return err; 1588 } 1589 } 1590 miss: 1591 #ifdef CONFIG_IP_FIB_TRIE_STATS 1592 this_cpu_inc(stats->semantic_match_miss); 1593 #endif 1594 goto backtrace; 1595 } 1596 EXPORT_SYMBOL_GPL(fib_table_lookup); 1597 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org