On Sat, Feb 04, 2023 at 09:12:31AM +0800, Guo Ren wrote: > On Sat, Feb 4, 2023 at 6:05 AM Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: > > > > arch_cpu_idle_dead() doesn't return. Make that more explicit with a > > BUG(). > > > > BUG() is preferable to unreachable() because BUG() is a more explicit > > failure mode and avoids undefined behavior like falling off the edge of > > the function into whatever code happens to be next. > > > > Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> > > --- > > arch/csky/kernel/smp.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/arch/csky/kernel/smp.c b/arch/csky/kernel/smp.c > > index b45d1073307f..0ec20efaf5fd 100644 > > --- a/arch/csky/kernel/smp.c > > +++ b/arch/csky/kernel/smp.c > > @@ -317,5 +317,7 @@ void arch_cpu_idle_dead(void) > > "jmpi csky_start_secondary" > > : > > : "r" (secondary_stack)); > > + > > + BUG(); > Why not: > diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c > index f26ab2675f7d..1d3bf903add2 100644 > --- a/kernel/sched/idle.c > +++ b/kernel/sched/idle.c > @@ -285,6 +285,7 @@ static void do_idle(void) > tick_nohz_idle_stop_tick(); > cpuhp_report_idle_dead(); > arch_cpu_idle_dead(); > + BUG(); Without the BUG() in csky arch_cpu_idle_dead(), the compiler will warn about arch_cpu_idle_dead() returning, because it's marked __noreturn but doesn't clearly return (as far as the compiler knows). And we want it marked __noreturn so we'll be more likely to catch such bugs at build time. And as a bonus we get better code generation and clearer code semantics which helps both humans and tooling understand the intent of the code. -- Josh
