# Re: \[PATCH net 2/2\] ipv4: make exception cache less predictible - From: kernel test robot \ - Date: 2021-08-31 07:48:52 - List: netdev - Page: https://ratatoskr.run/netdev/2021/08/11210566 - Thread: https://ratatoskr.run/llvm/2021/08/11210566/t.md ```text Hi Eric, I love your patch! Perhaps something to improve: [auto build test WARNING on net/master] url: https://github.com/0day-ci/linux/commits/Eric-Dumazet/inet-make-exception-handling-less-predictible/20210830-061726 base: https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git 57f780f1c43362b86fd23d20bd940e2468237716 :::::: branch date: 19 hours ago :::::: commit date: 19 hours ago config: x86_64-randconfig-c007-20210830 (attached as .config) compiler: clang version 14.0.0 (https://github.com/llvm/llvm-project 4b1fde8a2b681dad2ce0c082a5d6422caa06b0bc) 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/0day-ci/linux/commit/adf305d00ec06cb771dc960f0d7bd62d07561371 git remote add linux-review https://github.com/0day-ci/linux git fetch --no-tags linux-review Eric-Dumazet/inet-make-exception-handling-less-predictible/20210830-061726 git checkout adf305d00ec06cb771dc960f0d7bd62d07561371 # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64 clang-analyzer If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot clang-analyzer warnings: (new ones prefixed by >>) >> net/ipv4/route.c:575:7: warning: Dereference of null pointer [clang-analyzer-core.NullDereference] rt = rcu_dereference(fnhe->fnhe_rth_input); ^ net/ipv4/route.c:592:34: note: 'oldest' initialized to a null pointer value struct fib_nh_exception *fnhe, *oldest = NULL; ^~~~~~ net/ipv4/route.c:594:2: note: Loop condition is true. Entering loop body for (fnhe_p = &hash->chain; ; fnhe_p = &fnhe->fnhe_next) { ^ net/ipv4/route.c:595:10: note: Assuming the condition is false fnhe = rcu_dereference_protected(*fnhe_p, ^ include/linux/rcupdate.h:587:2: note: expanded from macro 'rcu_dereference_protected' __rcu_dereference_protected((p), (c), __rcu) ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ include/linux/rcupdate.h:396:19: note: expanded from macro '__rcu_dereference_protected' RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \ ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ include/linux/rcupdate.h:318:8: note: expanded from macro 'RCU_LOCKDEP_WARN' if ((c) && debug_lockdep_rcu_enabled() && !__warned) { \ ^ net/ipv4/route.c:595:10: note: Left side of '&&' is false fnhe = rcu_dereference_protected(*fnhe_p, ^ include/linux/rcupdate.h:587:2: note: expanded from macro 'rcu_dereference_protected' __rcu_dereference_protected((p), (c), __rcu) ^ include/linux/rcupdate.h:396:2: note: expanded from macro '__rcu_dereference_protected' RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \ ^ include/linux/rcupdate.h:318:11: note: expanded from macro 'RCU_LOCKDEP_WARN' if ((c) && debug_lockdep_rcu_enabled() && !__warned) { \ ^ net/ipv4/route.c:595:10: note: Loop condition is false. Exiting loop fnhe = rcu_dereference_protected(*fnhe_p, ^ include/linux/rcupdate.h:587:2: note: expanded from macro 'rcu_dereference_protected' __rcu_dereference_protected((p), (c), __rcu) ^ include/linux/rcupdate.h:396:2: note: expanded from macro '__rcu_dereference_protected' RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \ ^ include/linux/rcupdate.h:316:2: note: expanded from macro 'RCU_LOCKDEP_WARN' do { \ ^ net/ipv4/route.c:597:7: note: Assuming 'fnhe' is null if (!fnhe) ^~~~~ net/ipv4/route.c:597:3: note: Taking true branch if (!fnhe) ^ net/ipv4/route.c:598:4: note: Execution continues on line 605 break; ^ net/ipv4/route.c:605:20: note: Passing null pointer value via 1st parameter 'fnhe' fnhe_flush_routes(oldest); ^~~~~~ net/ipv4/route.c:605:2: note: Calling 'fnhe_flush_routes' fnhe_flush_routes(oldest); ^~~~~~~~~~~~~~~~~~~~~~~~~ net/ipv4/route.c:575:7: warning: Dereference of null pointer [clang-analyzer-core.NullDereference] rt = rcu_dereference(fnhe->fnhe_rth_input); ^ vim +575 net/ipv4/route.c 4895c771c7f006 David S. Miller 2012-07-17 570 2ffae99d1fac27 Timo Teräs 2013-06-27 571 static void fnhe_flush_routes(struct fib_nh_exception *fnhe) 2ffae99d1fac27 Timo Teräs 2013-06-27 572 { 2ffae99d1fac27 Timo Teräs 2013-06-27 573 struct rtable *rt; 2ffae99d1fac27 Timo Teräs 2013-06-27 574 2ffae99d1fac27 Timo Teräs 2013-06-27 @575 rt = rcu_dereference(fnhe->fnhe_rth_input); 2ffae99d1fac27 Timo Teräs 2013-06-27 576 if (rt) { 2ffae99d1fac27 Timo Teräs 2013-06-27 577 RCU_INIT_POINTER(fnhe->fnhe_rth_input, NULL); 95c47f9cf5e028 Wei Wang 2017-06-17 578 dst_dev_put(&rt->dst); 0830106c539001 Wei Wang 2017-06-17 579 dst_release(&rt->dst); 2ffae99d1fac27 Timo Teräs 2013-06-27 580 } 2ffae99d1fac27 Timo Teräs 2013-06-27 581 rt = rcu_dereference(fnhe->fnhe_rth_output); 2ffae99d1fac27 Timo Teräs 2013-06-27 582 if (rt) { 2ffae99d1fac27 Timo Teräs 2013-06-27 583 RCU_INIT_POINTER(fnhe->fnhe_rth_output, NULL); 95c47f9cf5e028 Wei Wang 2017-06-17 584 dst_dev_put(&rt->dst); 0830106c539001 Wei Wang 2017-06-17 585 dst_release(&rt->dst); 2ffae99d1fac27 Timo Teräs 2013-06-27 586 } 2ffae99d1fac27 Timo Teräs 2013-06-27 587 } 2ffae99d1fac27 Timo Teräs 2013-06-27 588 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org ``` ## Attachments - [.config.gz](https://ratatoskr.run/netdev/2021/08/11210566/attachment/0) (application/gzip, 27600 bytes)