tree: https://git.kernel.org/pub/scm/linux/kernel/git/ast/bpf.git timer head: eb86df61cd52ea2e05357f8ae2b77e9bf6d63463 commit: eb86df61cd52ea2e05357f8ae2b77e9bf6d63463 [4/4] bpf: Implement verifier support for validation of async callbacks. config: x86_64-randconfig-a002-20210622 (attached as .config) compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project b259740801d3515810ecc15bf0c24b0d476a1608) 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 # https://git.kernel.org/pub/scm/linux/kernel/git/ast/bpf.git/commit/?id=eb... git remote add ast https://git.kernel.org/pub/scm/linux/kernel/git/ast/bpf.git git fetch --no-tags ast timer git checkout eb86df61cd52ea2e05357f8ae2b77e9bf6d63463 # 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: kernel test robot <lkp(a)intel.com&gt; All warnings (new ones prefixed by >>): int ret; ^ 1 warning generated. vim +/ret +1022 kernel/bpf/helpers.c 7e26a76313f427 Alexei Starovoitov 2021-05-17 1011 7e26a76313f427 Alexei Starovoitov 2021-05-17 1012 static enum hrtimer_restart bpf_timer_cb(struct hrtimer *hrtimer) 7e26a76313f427 Alexei Starovoitov 2021-05-17 1013 { 7e26a76313f427 Alexei Starovoitov 2021-05-17 1014 struct bpf_hrtimer *t = container_of(hrtimer, struct bpf_hrtimer, timer); 7e26a76313f427 Alexei Starovoitov 2021-05-17 1015 struct bpf_map *map = t->map; 7e26a76313f427 Alexei Starovoitov 2021-05-17 1016 void *value = t->value; 7e26a76313f427 Alexei Starovoitov 2021-05-17 1017 struct bpf_timer_kern *timer = value + map->timer_off; 7e26a76313f427 Alexei Starovoitov 2021-05-17 1018 struct bpf_prog *prog; 7e26a76313f427 Alexei Starovoitov 2021-05-17 1019 void *callback_fn; 7e26a76313f427 Alexei Starovoitov 2021-05-17 1020 void *key; 7e26a76313f427 Alexei Starovoitov 2021-05-17 1021 u32 idx; 7e26a76313f427 Alexei Starovoitov 2021-05-17 @1022 int ret; 7e26a76313f427 Alexei Starovoitov 2021-05-17 1023 7e26a76313f427 Alexei Starovoitov 2021-05-17 1024 ____bpf_spin_lock(&timer->lock); 7e26a76313f427 Alexei Starovoitov 2021-05-17 1025 /* callback_fn and prog need to match. They're updated together 7e26a76313f427 Alexei Starovoitov 2021-05-17 1026 * and have to be read under lock. 7e26a76313f427 Alexei Starovoitov 2021-05-17 1027 */ 7e26a76313f427 Alexei Starovoitov 2021-05-17 1028 prog = t->prog; 7e26a76313f427 Alexei Starovoitov 2021-05-17 1029 callback_fn = t->callback_fn; 7e26a76313f427 Alexei Starovoitov 2021-05-17 1030 7e26a76313f427 Alexei Starovoitov 2021-05-17 1031 /* wrap bpf subprog invocation with prog->refcnt++ and -- to make 7e26a76313f427 Alexei Starovoitov 2021-05-17 1032 * sure that refcnt doesn't become zero when subprog is executing. 7e26a76313f427 Alexei Starovoitov 2021-05-17 1033 * Do it under lock to make sure that bpf_timer_start doesn't drop 7e26a76313f427 Alexei Starovoitov 2021-05-17 1034 * prev prog refcnt to zero before timer_cb has a chance to bump it. 7e26a76313f427 Alexei Starovoitov 2021-05-17 1035 */ 7e26a76313f427 Alexei Starovoitov 2021-05-17 1036 bpf_prog_inc(prog); 7e26a76313f427 Alexei Starovoitov 2021-05-17 1037 ____bpf_spin_unlock(&timer->lock); 7e26a76313f427 Alexei Starovoitov 2021-05-17 1038 7e26a76313f427 Alexei Starovoitov 2021-05-17 1039 /* bpf_timer_cb() runs in hrtimer_run_softirq. It doesn't migrate and 7e26a76313f427 Alexei Starovoitov 2021-05-17 1040 * cannot be preempted by another bpf_timer_cb() on the same cpu. 7e26a76313f427 Alexei Starovoitov 2021-05-17 1041 * Remember the timer this callback is servicing to prevent 7e26a76313f427 Alexei Starovoitov 2021-05-17 1042 * deadlock if callback_fn() calls bpf_timer_cancel() on the same timer. 7e26a76313f427 Alexei Starovoitov 2021-05-17 1043 */ 7e26a76313f427 Alexei Starovoitov 2021-05-17 1044 this_cpu_write(hrtimer_running, t); 7e26a76313f427 Alexei Starovoitov 2021-05-17 1045 if (map->map_type == BPF_MAP_TYPE_ARRAY) { 7e26a76313f427 Alexei Starovoitov 2021-05-17 1046 struct bpf_array *array = container_of(map, struct bpf_array, map); 7e26a76313f427 Alexei Starovoitov 2021-05-17 1047 7e26a76313f427 Alexei Starovoitov 2021-05-17 1048 /* compute the key */ 7e26a76313f427 Alexei Starovoitov 2021-05-17 1049 idx = ((char *)value - array->value) / array->elem_size; 7e26a76313f427 Alexei Starovoitov 2021-05-17 1050 key = &idx; 7e26a76313f427 Alexei Starovoitov 2021-05-17 1051 } else { /* hash or lru */ 7e26a76313f427 Alexei Starovoitov 2021-05-17 1052 key = value - round_up(map->key_size, 8); 7e26a76313f427 Alexei Starovoitov 2021-05-17 1053 } 7e26a76313f427 Alexei Starovoitov 2021-05-17 1054 7e26a76313f427 Alexei Starovoitov 2021-05-17 1055 ret = BPF_CAST_CALL(callback_fn)((u64)(long)map, 7e26a76313f427 Alexei Starovoitov 2021-05-17 1056 (u64)(long)key, 7e26a76313f427 Alexei Starovoitov 2021-05-17 1057 (u64)(long)value, 0, 0); 7e26a76313f427 Alexei Starovoitov 2021-05-17 1058 bpf_prog_put(prog); 7e26a76313f427 Alexei Starovoitov 2021-05-17 1059 7e26a76313f427 Alexei Starovoitov 2021-05-17 1060 this_cpu_write(hrtimer_running, NULL); 7e26a76313f427 Alexei Starovoitov 2021-05-17 1061 return HRTIMER_NORESTART; 7e26a76313f427 Alexei Starovoitov 2021-05-17 1062 } 7e26a76313f427 Alexei Starovoitov 2021-05-17 1063 :::::: The code at line 1022 was first introduced by commit :::::: 7e26a76313f4274c6013a7565411f3f7b6773b29 bpf: Introduce bpf_timer :::::: TO: Alexei Starovoitov <ast(a)kernel.org&gt; :::::: CC: Alexei Starovoitov <ast(a)kernel.org&gt; --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org