On Mon, Jul 29, 2019 at 05:59:04PM +0100, Dietmar Eggemann wrote: > On 7/29/19 5:54 PM, Peter Zijlstra wrote: > > On Fri, Jul 26, 2019 at 12:18:19PM +0200, luca abeni wrote: > >> Hi Dietmar, > >> > >> On Fri, 26 Jul 2019 09:27:56 +0100 > >> Dietmar Eggemann <[email protected]> wrote: > >> > >>> To make the decision whether to set rq or running bw to 0 in underflow > >>> case use the return value of SCHED_WARN_ON() rather than an extra if > >>> condition. > >> > >> I think I tried this at some point, but if I remember well this > >> solution does not work correctly when SCHED_DEBUG is not enabled. > > > > Well, it 'works' in so far that it compiles. But it might not be what > > one expects. That is, for !SCHED_DEBUG the return value is an > > unconditional false. > > > > In this case I think that's fine, the WARN _should_ not be happending. > > But there is commit 6d3aed3d ("sched/debug: Fix SCHED_WARN_ON() to > return a value on !CONFIG_SCHED_DEBUG as well")? > > But it doesn't work with !CONFIG_SCHED_DEBUG > > What compiles and work is (at least on Arm64). > > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 4012f98b9d26..494a767a4091 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -78,7 +78,7 @@ > #ifdef CONFIG_SCHED_DEBUG > # define SCHED_WARN_ON(x) WARN_ONCE(x, #x) > #else > -# define SCHED_WARN_ON(x) ({ (void)(x), 0; }) > +# define SCHED_WARN_ON(x) ({ (void)(x), x; })
Why doesn't the ,0 compile? That should work just fine. The thing is, the two existing users: kernel/sched/fair.c: if (SCHED_WARN_ON(!se->on_rq)) kernel/sched/fair.c: if (SCHED_WARN_ON(!se->on_rq)) seem to compile just fine with it.
