| Message ID | f860f3a1c1a53c437a99abc53e8f1a798aef6881.1675461757.git.jpoimboe@kernel.org |
|---|---|
| State | New |
| Headers | show |
| Series | cpu,sched: Mark arch_cpu_idle_dead() __noreturn | expand |
On Sat, Feb 4, 2023 at 6:05 AM Josh Poimboeuf <jpoimboe@kernel.org> 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@kernel.org> > --- > 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(); } arch_cpu_idle_enter(); > } > #endif > -- > 2.39.0 >
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@kernel.org> 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@kernel.org> > > --- > > 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.
On Sat, Feb 4, 2023 at 10:29 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote: > > 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@kernel.org> 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@kernel.org> > > > --- > > > 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. Thx for the clarification. Acked-by: Guo Ren <guoren@kernel.org> > > -- > Josh
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(); } #endif
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@kernel.org> --- arch/csky/kernel/smp.c | 2 ++ 1 file changed, 2 insertions(+)