[kbuild-all] Re: [peterz-queue:sched/core 13/19] kernel/sched/fair.c:892:34: warning: variable 'stats' set but not used

Hi! On Sat, Sep 11, 2021 at 02:20:49PM +0200, Peter Zijlstra wrote: > On Sat, Sep 11, 2021 at 02:21:26AM +0800, kernel test robot wrote: > > compiler: m68k-linux-gcc (GCC) 11.2.0 > > > kernel/sched/fair.c: In function 'update_curr': > > kernel/sched/fair.c:860:42: warning: unused variable 'stats' [-Wunused-variable] > > 860 | struct sched_statistics *stats = __schedstats_from_se(curr); > > | ^~~~~ > > OK, compiler guys, this code reads like: > > #define schedstats_enabled() (0) > #define __schedstat_set(x, y) do { } while (0) > > > if (schedstats_enabled()) { > struct sched_statistics *stats = __schedstats_from_se(curr); > > __schedstat_set(stats->exec_max, > max(delta_exec, stats->exec_max)); > } > > So yes, we initialize a variable that then isn't used, but the whole > bloody thing is inside if (0) which will not ever get ran *anyway*. > > This is a crap warning if ever I saw one... Yes, we really should warn "do not use a preprocessor macro if what you want is a function"? The variable really *is* unused, with this macro.

If we would remove dead code before warning about unused variables there would be many *more* false positives, fwiw.