* Re: [peterz-queue:sched/core 13/19] kernel/sched/fair.c:892:34: warning: variable 'stats' set but not used [not found] <202109110214.oh62aoIq-lkp@intel.com> @ 2021-09-11 12:20 ` Peter Zijlstra 2021-09-11 21:30 ` Segher Boessenkool 0 siblings, 1 reply; 3+ messages in thread From: Peter Zijlstra @ 2021-09-11 12:20 UTC (permalink / raw) To: kernel test robot; +Cc: Yafang Shao, kbuild-all, linux-kernel, linux-toolchains 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... ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [peterz-queue:sched/core 13/19] kernel/sched/fair.c:892:34: warning: variable 'stats' set but not used 2021-09-11 12:20 ` [peterz-queue:sched/core 13/19] kernel/sched/fair.c:892:34: warning: variable 'stats' set but not used Peter Zijlstra @ 2021-09-11 21:30 ` Segher Boessenkool 2021-09-11 22:33 ` Peter Zijlstra 0 siblings, 1 reply; 3+ messages in thread From: Segher Boessenkool @ 2021-09-11 21:30 UTC (permalink / raw) To: Peter Zijlstra Cc: kernel test robot, Yafang Shao, kbuild-all, linux-kernel, linux-toolchains 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. Segher ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [peterz-queue:sched/core 13/19] kernel/sched/fair.c:892:34: warning: variable 'stats' set but not used 2021-09-11 21:30 ` Segher Boessenkool @ 2021-09-11 22:33 ` Peter Zijlstra 0 siblings, 0 replies; 3+ messages in thread From: Peter Zijlstra @ 2021-09-11 22:33 UTC (permalink / raw) To: Segher Boessenkool Cc: kernel test robot, Yafang Shao, kbuild-all, linux-kernel, linux-toolchains On Sat, Sep 11, 2021 at 04:30:41PM -0500, Segher Boessenkool wrote: > 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. Why would I want to write a bunch of one-off functions and preprocessor guard them? That's going to be a mess. > If we would remove dead code before warning about unused variables > there would be many *more* false positives, fwiw. Not if you also remove any variables declared in dead code and all variables only used in the dead code. ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2021-09-11 22:33 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- [not found] <202109110214.oh62aoIq-lkp@intel.com> 2021-09-11 12:20 ` [peterz-queue:sched/core 13/19] kernel/sched/fair.c:892:34: warning: variable 'stats' set but not used Peter Zijlstra 2021-09-11 21:30 ` Segher Boessenkool 2021-09-11 22:33 ` Peter Zijlstra
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