Messages in this thread | | | Date | Wed, 1 Nov 2017 09:34:55 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH v2] sched/sysctl: Fix attributes of some extern declarations |
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* Matthias Kaehlcke <mka@chromium.org> wrote:
> El Tue, Oct 30, 2017 at 10:57:58AM +0100 Ingo Molnar ha dit: > > > * Matthias Kaehlcke <mka@chromium.org> wrote: > > > > > The definition of sysctl_sched_migration_cost, sysctl_sched_nr_migrate > > > and sysctl_sched_time_avg includes the attribute const_debug. This > > > attribute is not part of the extern declaration of these variables in > > > include/linux/sched/sysctl.h, as a result clang generates warnings like > > > this: > > > > > > kernel/sched/sched.h:1618:33: warning: section attribute is specified on > > > redeclared variable [-Wsection] > > > extern const_debug unsigned int sysctl_sched_time_avg; > > > ^ > > > ./include/linux/sched/sysctl.h:42:21: note: previous declaration is here > > > extern unsigned int sysctl_sched_time_avg; > > > > > > The header only declares the variables when CONFIG_SCHED_DEBUG is defined, > > > therefore it is not necessary to duplicate the definition of const_debug. > > > Instead we can use the attribute __read_mostly, which is the expansion of > > > const_debug when CONFIG_SCHED_DEBUG is set. > > > > > > Signed-off-by: Matthias Kaehlcke <mka@chromium.org> > > > Reviewed-by: Nick Desaulniers <nick.desaulniers@gmail.com> > > > --- > > > Changes in v2: > > > - removed pointless include of linux/static_key.h > > > - added Reviewed-by tag > > > > > > include/linux/sched/sysctl.h | 6 +++--- > > > 1 file changed, 3 insertions(+), 3 deletions(-) > > > > > > diff --git a/include/linux/sched/sysctl.h b/include/linux/sched/sysctl.h > > > index 0f5ecd4d298e..d34c823f3d36 100644 > > > --- a/include/linux/sched/sysctl.h > > > +++ b/include/linux/sched/sysctl.h > > > @@ -37,9 +37,9 @@ extern unsigned int sysctl_numa_balancing_scan_period_max; > > > extern unsigned int sysctl_numa_balancing_scan_size; > > > > > > #ifdef CONFIG_SCHED_DEBUG > > > -extern unsigned int sysctl_sched_migration_cost; > > > -extern unsigned int sysctl_sched_nr_migrate; > > > -extern unsigned int sysctl_sched_time_avg; > > > +extern __read_mostly unsigned int sysctl_sched_migration_cost; > > > +extern __read_mostly unsigned int sysctl_sched_nr_migrate; > > > +extern __read_mostly unsigned int sysctl_sched_time_avg; > > > > So I hate this change, because it pointlessly duplicates an attribute that should > > only matter at the definition site. > > It's certainly not ideal, and then again essentially the same is done > in kernel/sched/sched.h, just that here the specific attribute is > hidden behind const_debug.
Ok - and that indeed is a problem and makes the Clang build warning useful, as there are two conflicting prototypes and one definition.
I'll apply your fix.
Thanks,
Ingo
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