:::::: :::::: Manual check reason: "low confidence static check warning: kernel/sched/fair.c:9330:6: warning: Value stored to 'icpu' during its initialization is never read [clang-analyzer-deadcode.DeadStores]" ::::::
CC: l...@lists.linux.dev CC: kbuild-...@lists.01.org BCC: l...@intel.com In-Reply-To: <20220619120451.95251-8-wuyun.a...@bytedance.com> References: <20220619120451.95251-8-wuyun.a...@bytedance.com> TO: Abel Wu <wuyun.a...@bytedance.com> TO: Peter Zijlstra <pet...@infradead.org> TO: Mel Gorman <mgor...@suse.de> TO: Vincent Guittot <vincent.guit...@linaro.org> CC: Josh Don <josh...@google.com> CC: Chen Yu <yu.c.c...@intel.com> CC: Tim Chen <tim.c.c...@linux.intel.com> CC: K Prateek Nayak <kprateek.na...@amd.com> CC: "Gautham R . Shenoy" <gautham.she...@amd.com> CC: linux-ker...@vger.kernel.org CC: Abel Wu <wuyun.a...@bytedance.com> Hi Abel, Thank you for the patch! Perhaps something to improve: [auto build test WARNING on tip/sched/core] [also build test WARNING on linus/master v5.19-rc2 next-20220617] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in https://git-scm.com/docs/git-format-patch] url: https://github.com/intel-lab-lkp/linux/commits/Abel-Wu/sched-fair-improve-scan-efficiency-of-SIS/20220619-200743 base: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git f3dd3f674555bd9455c5ae7fafce0696bd9931b3 :::::: branch date: 2 days ago :::::: commit date: 2 days ago config: s390-randconfig-c005-20220619 (https://download.01.org/0day-ci/archive/20220621/202206211517.bchsifsf-...@intel.com/config) compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project af6d2a0b6825e71965f3e2701a63c239fa0ad70f) 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 s390 cross compiling tool for clang build # apt-get install binutils-s390x-linux-gnu # https://github.com/intel-lab-lkp/linux/commit/32fe13cd7aa184ed349d698ebf6f420fa426dd73 git remote add linux-review https://github.com/intel-lab-lkp/linux git fetch --no-tags linux-review Abel-Wu/sched-fair-improve-scan-efficiency-of-SIS/20220619-200743 git checkout 32fe13cd7aa184ed349d698ebf6f420fa426dd73 # save the config file COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=s390 clang-analyzer If you fix the issue, kindly add following tag where applicable Reported-by: kernel test robot <l...@intel.com> clang-analyzer warnings: (new ones prefixed by >>) ^~~~~~~~~~~~~~~~~~~~~~ kernel/sched/fair.c:9670:2: note: Calling 'update_sd_lb_stats' update_sd_lb_stats(env, &sds); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~ kernel/sched/fair.c:9422:7: note: Assuming 'local_group' is 0 if (local_group) { ^~~~~~~~~~~ kernel/sched/fair.c:9422:3: note: Taking false branch if (local_group) { ^ kernel/sched/fair.c:9431:3: note: Calling 'update_sg_lb_stats' update_sg_lb_stats(env, sds, sg, sgs, &sg_status); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ kernel/sched/fair.c:8766:16: note: Assuming 'group' is not equal to field 'local' local_group = group == sds->local; ^~~~~~~~~~~~~~~~~~~ kernel/sched/fair.c:8769:2: note: Assuming 'i' is >= 'nr_cpu_ids' for_each_cpu_and(i, sched_group_span(group), env->cpus) { ^ include/linux/cpumask.h:326:3: note: expanded from macro 'for_each_cpu_and' (cpu) < nr_cpu_ids;) ^~~~~~~~~~~~~~~~~~ kernel/sched/fair.c:8769:2: note: Loop condition is false. Execution continues on line 8828 for_each_cpu_and(i, sched_group_span(group), env->cpus) { ^ include/linux/cpumask.h:324:2: note: expanded from macro 'for_each_cpu_and' for ((cpu) = -1; \ ^ kernel/sched/fair.c:8833:7: note: 'local_group' is 0 if (!local_group && env->sd->flags & SD_ASYM_PACKING && ^~~~~~~~~~~ kernel/sched/fair.c:8833:6: note: Left side of '&&' is true if (!local_group && env->sd->flags & SD_ASYM_PACKING && ^ kernel/sched/fair.c:8833:22: note: Assuming the condition is true if (!local_group && env->sd->flags & SD_ASYM_PACKING && ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ kernel/sched/fair.c:8833:6: note: Left side of '&&' is true if (!local_group && env->sd->flags & SD_ASYM_PACKING && ^ kernel/sched/fair.c:8834:6: note: Assuming field 'idle' is not equal to CPU_NOT_IDLE env->idle != CPU_NOT_IDLE && sgs->sum_h_nr_running && ^~~~~~~~~~~~~~~~~~~~~~~~~ kernel/sched/fair.c:8833:6: note: Left side of '&&' is true if (!local_group && env->sd->flags & SD_ASYM_PACKING && ^ kernel/sched/fair.c:8834:35: note: Assuming field 'sum_h_nr_running' is not equal to 0 env->idle != CPU_NOT_IDLE && sgs->sum_h_nr_running && ^~~~~~~~~~~~~~~~~~~~~ kernel/sched/fair.c:8833:6: note: Left side of '&&' is true if (!local_group && env->sd->flags & SD_ASYM_PACKING && ^ kernel/sched/fair.c:8835:6: note: Calling 'sched_asym' sched_asym(env, sds, sgs, group)) { ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ kernel/sched/fair.c:8727:7: note: Access to field 'flags' results in a dereference of a null pointer (loaded from field 'local') if ((sds->local->flags & SD_SHARE_CPUCAPACITY) || ^ ~~~~~ kernel/sched/fair.c:8828:24: warning: Access to field 'sgc' results in a dereference of a null pointer (loaded from variable 'group') [clang-analyzer-core.NullDereference] sgs->group_capacity = group->sgc->capacity; ^ kernel/sched/fair.c:9670:2: note: Calling 'update_sd_lb_stats' update_sd_lb_stats(env, &sds); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~ kernel/sched/fair.c:9412:2: note: 'sg' initialized here struct sched_group *sg = env->sd->groups; ^~~~~~~~~~~~~~~~~~~~~~ kernel/sched/fair.c:9422:7: note: Assuming 'local_group' is 0 if (local_group) { ^~~~~~~~~~~ kernel/sched/fair.c:9422:3: note: Taking false branch if (local_group) { ^ kernel/sched/fair.c:9431:32: note: Passing 'sg' via 3rd parameter 'group' update_sg_lb_stats(env, sds, sg, sgs, &sg_status); ^~ kernel/sched/fair.c:9431:3: note: Calling 'update_sg_lb_stats' update_sg_lb_stats(env, sds, sg, sgs, &sg_status); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ kernel/sched/fair.c:8766:16: note: Assuming 'group' is equal to field 'local' local_group = group == sds->local; ^~~~~~~~~~~~~~~~~~~ kernel/sched/fair.c:8766:16: note: Assuming pointer value is null local_group = group == sds->local; ^~~~~~~~~~~~~~~~~~~ kernel/sched/fair.c:8769:2: note: Assuming 'i' is >= 'nr_cpu_ids' for_each_cpu_and(i, sched_group_span(group), env->cpus) { ^ include/linux/cpumask.h:326:3: note: expanded from macro 'for_each_cpu_and' (cpu) < nr_cpu_ids;) ^~~~~~~~~~~~~~~~~~ kernel/sched/fair.c:8769:2: note: Loop condition is false. Execution continues on line 8828 for_each_cpu_and(i, sched_group_span(group), env->cpus) { ^ include/linux/cpumask.h:324:2: note: expanded from macro 'for_each_cpu_and' for ((cpu) = -1; \ ^ kernel/sched/fair.c:8828:24: note: Access to field 'sgc' results in a dereference of a null pointer (loaded from variable 'group') sgs->group_capacity = group->sgc->capacity; ^~~~~ >> kernel/sched/fair.c:9330:6: warning: Value stored to 'icpu' during its >> initialization is never read [clang-analyzer-deadcode.DeadStores] int icpu = sds->idle_cpu, this = env->dst_cpu; ^~~~ ~~~~~~~~~~~~~ kernel/sched/fair.c:9330:6: note: Value stored to 'icpu' during its initialization is never read int icpu = sds->idle_cpu, this = env->dst_cpu; ^~~~ ~~~~~~~~~~~~~ >> kernel/sched/fair.c:9352:4: warning: Value stored to 'icpu' is never read >> [clang-analyzer-deadcode.DeadStores] icpu = this; ^ ~~~~ kernel/sched/fair.c:9352:4: note: Value stored to 'icpu' is never read icpu = this; ^ ~~~~ kernel/sched/fair.c:10040:25: warning: Dereference of null pointer [clang-analyzer-core.NullDereference] struct cpumask *cpus = this_cpu_cpumask_var_ptr(load_balance_mask); ^ include/linux/cpumask.h:761:37: note: expanded from macro 'this_cpu_cpumask_var_ptr' #define this_cpu_cpumask_var_ptr(x) this_cpu_ptr(x) ^ include/linux/percpu-defs.h:252:27: note: expanded from macro 'this_cpu_ptr' #define this_cpu_ptr(ptr) raw_cpu_ptr(ptr) ^ include/linux/percpu-defs.h:242:2: note: expanded from macro 'raw_cpu_ptr' arch_raw_cpu_ptr(ptr); \ ^ include/asm-generic/percpu.h:44:31: note: expanded from macro 'arch_raw_cpu_ptr' #define arch_raw_cpu_ptr(ptr) SHIFT_PERCPU_PTR(ptr, __my_cpu_offset) ^ include/linux/percpu-defs.h:231:2: note: expanded from macro 'SHIFT_PERCPU_PTR' RELOC_HIDE((typeof(*(__p)) __kernel __force *)(__p), (__offset)) ^ include/linux/compiler.h:170:28: note: expanded from macro 'RELOC_HIDE' (typeof(ptr)) (__ptr + (off)); }) ^ kernel/sched/fair.c:10462:13: note: Assuming 'idle' is equal to CPU_IDLE int busy = idle != CPU_IDLE && !sched_idle_cpu(cpu); ^~~~~~~~~~~~~~~~ kernel/sched/fair.c:10462:30: note: Left side of '&&' is false int busy = idle != CPU_IDLE && !sched_idle_cpu(cpu); ^ kernel/sched/fair.c:10472:2: note: Left side of '||' is false for_each_domain(cpu, sd) { ^ kernel/sched/sched.h:1716:14: note: expanded from macro 'for_each_domain' for (__sd = rcu_dereference_check_sched_domain(cpu_rq(cpu)->sd); \ ^ kernel/sched/sched.h:1705:2: note: expanded from macro 'rcu_dereference_check_sched_domain' rcu_dereference_check((p), \ ^ include/linux/rcupdate.h:532:2: note: expanded from macro 'rcu_dereference_check' __rcu_dereference_check((p), __UNIQUE_ID(rcu), \ ^ note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all) include/asm-generic/rwonce.h:49:2: note: expanded from macro 'READ_ONCE' compiletime_assert_rwonce_type(x); \ ^ include/asm-generic/rwonce.h:36:21: note: expanded from macro 'compiletime_assert_rwonce_type' compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long), \ ^ include/linux/compiler_types.h:319:3: note: expanded from macro '__native_word' (sizeof(t) == sizeof(char) || sizeof(t) == sizeof(short) || \ ^ kernel/sched/fair.c:10472:2: note: Left side of '||' is false for_each_domain(cpu, sd) { ^ kernel/sched/sched.h:1716:14: note: expanded from macro 'for_each_domain' for (__sd = rcu_dereference_check_sched_domain(cpu_rq(cpu)->sd); \ ^ kernel/sched/sched.h:1705:2: note: expanded from macro 'rcu_dereference_check_sched_domain' rcu_dereference_check((p), \ ^ include/linux/rcupdate.h:532:2: note: expanded from macro 'rcu_dereference_check' __rcu_dereference_check((p), __UNIQUE_ID(rcu), \ ^ note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all) include/asm-generic/rwonce.h:49:2: note: expanded from macro 'READ_ONCE' compiletime_assert_rwonce_type(x); \ ^ include/asm-generic/rwonce.h:36:21: note: expanded from macro 'compiletime_assert_rwonce_type' compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long), \ ^ include/linux/compiler_types.h:319:3: note: expanded from macro '__native_word' (sizeof(t) == sizeof(char) || sizeof(t) == sizeof(short) || \ ^ kernel/sched/fair.c:10472:2: note: Left side of '||' is false for_each_domain(cpu, sd) { ^ kernel/sched/sched.h:1716:14: note: expanded from macro 'for_each_domain' for (__sd = rcu_dereference_check_sched_domain(cpu_rq(cpu)->sd); \ ^ kernel/sched/sched.h:1705:2: note: expanded from macro 'rcu_dereference_check_sched_domain' rcu_dereference_check((p), \ ^ include/linux/rcupdate.h:532:2: note: expanded from macro 'rcu_dereference_check' __rcu_dereference_check((p), __UNIQUE_ID(rcu), \ ^ note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all) include/asm-generic/rwonce.h:49:2: note: expanded from macro 'READ_ONCE' compiletime_assert_rwonce_type(x); \ ^ include/asm-generic/rwonce.h:36:21: note: expanded from macro 'compiletime_assert_rwonce_type' compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long), \ ^ include/linux/compiler_types.h:319:3: note: expanded from macro '__native_word' (sizeof(t) == sizeof(char) || sizeof(t) == sizeof(short) || \ ^ kernel/sched/fair.c:10472:2: note: Left side of '||' is true for_each_domain(cpu, sd) { vim +/icpu +9330 kernel/sched/fair.c 57abff067a0848 Vincent Guittot 2019-10-18 9325 ba6ee6cee1ed2f Abel Wu 2022-06-19 9326 static void sd_update_state(struct lb_env *env, struct sd_lb_stats *sds) ba6ee6cee1ed2f Abel Wu 2022-06-19 9327 { fcc108377a7cf7 Abel Wu 2022-06-19 9328 struct sched_domain_shared *sd_smt_shared = env->sd->shared; fcc108377a7cf7 Abel Wu 2022-06-19 9329 enum sd_state new = sds->sd_state; 32fe13cd7aa184 Abel Wu 2022-06-19 @9330 int icpu = sds->idle_cpu, this = env->dst_cpu; fcc108377a7cf7 Abel Wu 2022-06-19 9331 fcc108377a7cf7 Abel Wu 2022-06-19 9332 /* fcc108377a7cf7 Abel Wu 2022-06-19 9333 * Parallel updating can hardly contribute accuracy to fcc108377a7cf7 Abel Wu 2022-06-19 9334 * the filter, besides it can be one of the burdens on fcc108377a7cf7 Abel Wu 2022-06-19 9335 * cache traffic. fcc108377a7cf7 Abel Wu 2022-06-19 9336 */ fcc108377a7cf7 Abel Wu 2022-06-19 9337 if (cmpxchg(&sd_smt_shared->updating, 0, 1)) fcc108377a7cf7 Abel Wu 2022-06-19 9338 return; fcc108377a7cf7 Abel Wu 2022-06-19 9339 32fe13cd7aa184 Abel Wu 2022-06-19 9340 /* 32fe13cd7aa184 Abel Wu 2022-06-19 9341 * The dst_cpu is likely to be fed with tasks soon. 32fe13cd7aa184 Abel Wu 2022-06-19 9342 * If it is the only unoccupied cpu in this domain, 32fe13cd7aa184 Abel Wu 2022-06-19 9343 * we still handle it the same way as as_has_icpus 32fe13cd7aa184 Abel Wu 2022-06-19 9344 * but turn the SMT into the unstable state, rather 32fe13cd7aa184 Abel Wu 2022-06-19 9345 * than waiting to the end of load balancing since 32fe13cd7aa184 Abel Wu 2022-06-19 9346 * it's also important that update the filter as 32fe13cd7aa184 Abel Wu 2022-06-19 9347 * early as possible to keep it fresh. 32fe13cd7aa184 Abel Wu 2022-06-19 9348 */ 32fe13cd7aa184 Abel Wu 2022-06-19 9349 if (new == sd_is_busy) { 32fe13cd7aa184 Abel Wu 2022-06-19 9350 if (idle_cpu(this) || sched_idle_cpu(this)) { 32fe13cd7aa184 Abel Wu 2022-06-19 9351 new = sd_may_idle; 32fe13cd7aa184 Abel Wu 2022-06-19 @9352 icpu = this; 32fe13cd7aa184 Abel Wu 2022-06-19 9353 } 32fe13cd7aa184 Abel Wu 2022-06-19 9354 } 32fe13cd7aa184 Abel Wu 2022-06-19 9355 fcc108377a7cf7 Abel Wu 2022-06-19 9356 /* fcc108377a7cf7 Abel Wu 2022-06-19 9357 * There is at least one unoccupied cpu available, so fcc108377a7cf7 Abel Wu 2022-06-19 9358 * propagate it to the filter to avoid false negative fcc108377a7cf7 Abel Wu 2022-06-19 9359 * issue which could result in lost tracking of some fcc108377a7cf7 Abel Wu 2022-06-19 9360 * idle cpus thus throughupt downgraded. fcc108377a7cf7 Abel Wu 2022-06-19 9361 */ fcc108377a7cf7 Abel Wu 2022-06-19 9362 if (new != sd_is_busy) { 32fe13cd7aa184 Abel Wu 2022-06-19 9363 /* 32fe13cd7aa184 Abel Wu 2022-06-19 9364 * The sd_may_idle state is taken into 32fe13cd7aa184 Abel Wu 2022-06-19 9365 * consideration as well because from 32fe13cd7aa184 Abel Wu 2022-06-19 9366 * here we couldn't actually know task 32fe13cd7aa184 Abel Wu 2022-06-19 9367 * migrations would happen or not. 32fe13cd7aa184 Abel Wu 2022-06-19 9368 */ fcc108377a7cf7 Abel Wu 2022-06-19 9369 if (!test_idle_cpus(this)) fcc108377a7cf7 Abel Wu 2022-06-19 9370 set_idle_cpus(this, true); fcc108377a7cf7 Abel Wu 2022-06-19 9371 } else { fcc108377a7cf7 Abel Wu 2022-06-19 9372 /* fcc108377a7cf7 Abel Wu 2022-06-19 9373 * Nothing changes so nothing to update or fcc108377a7cf7 Abel Wu 2022-06-19 9374 * propagate. fcc108377a7cf7 Abel Wu 2022-06-19 9375 */ fcc108377a7cf7 Abel Wu 2022-06-19 9376 if (sd_smt_shared->state == sd_is_busy) fcc108377a7cf7 Abel Wu 2022-06-19 9377 goto out; 32fe13cd7aa184 Abel Wu 2022-06-19 9378 32fe13cd7aa184 Abel Wu 2022-06-19 9379 /* 32fe13cd7aa184 Abel Wu 2022-06-19 9380 * Allow false positive to exist for some time 32fe13cd7aa184 Abel Wu 2022-06-19 9381 * to make a tradeoff of accuracy of the filter 32fe13cd7aa184 Abel Wu 2022-06-19 9382 * for relieving cache traffic. 32fe13cd7aa184 Abel Wu 2022-06-19 9383 */ 32fe13cd7aa184 Abel Wu 2022-06-19 9384 if (sd_smt_shared->state == sd_has_icpus) { 32fe13cd7aa184 Abel Wu 2022-06-19 9385 new = sd_may_idle; 32fe13cd7aa184 Abel Wu 2022-06-19 9386 goto update; 32fe13cd7aa184 Abel Wu 2022-06-19 9387 } 32fe13cd7aa184 Abel Wu 2022-06-19 9388 32fe13cd7aa184 Abel Wu 2022-06-19 9389 /* 32fe13cd7aa184 Abel Wu 2022-06-19 9390 * If the false positive issue has already been 32fe13cd7aa184 Abel Wu 2022-06-19 9391 * there for a while, a correction of the filter 32fe13cd7aa184 Abel Wu 2022-06-19 9392 * is needed. 32fe13cd7aa184 Abel Wu 2022-06-19 9393 */ fcc108377a7cf7 Abel Wu 2022-06-19 9394 } fcc108377a7cf7 Abel Wu 2022-06-19 9395 fcc108377a7cf7 Abel Wu 2022-06-19 9396 sd_update_icpus(this, sds->idle_cpu); 32fe13cd7aa184 Abel Wu 2022-06-19 9397 update: fcc108377a7cf7 Abel Wu 2022-06-19 9398 sd_smt_shared->state = new; fcc108377a7cf7 Abel Wu 2022-06-19 9399 out: fcc108377a7cf7 Abel Wu 2022-06-19 9400 xchg(&sd_smt_shared->updating, 0); ba6ee6cee1ed2f Abel Wu 2022-06-19 9401 } ba6ee6cee1ed2f Abel Wu 2022-06-19 9402 -- 0-DAY CI Kernel Test Service https://01.org/lkp _______________________________________________ kbuild mailing list -- kbuild@lists.01.org To unsubscribe send an email to kbuild-le...@lists.01.org
