| Message ID | 20220608144516.871305980@infradead.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | cpuidle,rcu: Cleanup the mess | expand |
On Wed, Jun 08, 2022 at 04:27:38PM +0200, Peter Zijlstra wrote: > All callers should still have RCU enabled. IIUC with that true we should be able to drop the RCU_NONIDLE() from drivers/perf/arm_pmu.c, as we only needed that for an invocation via a pm notifier. I should be able to give that a spin on some hardware. > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- > kernel/cpu_pm.c | 9 --------- > 1 file changed, 9 deletions(-) > > --- a/kernel/cpu_pm.c > +++ b/kernel/cpu_pm.c > @@ -30,16 +30,9 @@ static int cpu_pm_notify(enum cpu_pm_eve > { > int ret; > > - /* > - * This introduces a RCU read critical section, which could be > - * disfunctional in cpu idle. Copy RCU_NONIDLE code to let RCU know > - * this. > - */ > - rcu_irq_enter_irqson(); > rcu_read_lock(); > ret = raw_notifier_call_chain(&cpu_pm_notifier.chain, event, NULL); > rcu_read_unlock(); > - rcu_irq_exit_irqson(); To make this easier to debug, is it worth adding an assertion that RCU is watching here? e.g. RCU_LOCKDEP_WARN(!rcu_is_watching(), "cpu_pm_notify() used illegally from EQS"); > > return notifier_to_errno(ret); > } > @@ -49,11 +42,9 @@ static int cpu_pm_notify_robust(enum cpu > unsigned long flags; > int ret; > > - rcu_irq_enter_irqson(); > raw_spin_lock_irqsave(&cpu_pm_notifier.lock, flags); > ret = raw_notifier_call_chain_robust(&cpu_pm_notifier.chain, event_up, event_down, NULL); > raw_spin_unlock_irqrestore(&cpu_pm_notifier.lock, flags); > - rcu_irq_exit_irqson(); ... and likewise here? Thanks, Mark. > > return notifier_to_errno(ret); > } > >
On Tue, Jun 14, 2022 at 05:13:16PM +0100, Mark Rutland wrote: > On Wed, Jun 08, 2022 at 04:27:38PM +0200, Peter Zijlstra wrote: > > All callers should still have RCU enabled. > > IIUC with that true we should be able to drop the RCU_NONIDLE() from > drivers/perf/arm_pmu.c, as we only needed that for an invocation via a pm > notifier. > > I should be able to give that a spin on some hardware. > > > > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > > --- > > kernel/cpu_pm.c | 9 --------- > > 1 file changed, 9 deletions(-) > > > > --- a/kernel/cpu_pm.c > > +++ b/kernel/cpu_pm.c > > @@ -30,16 +30,9 @@ static int cpu_pm_notify(enum cpu_pm_eve > > { > > int ret; > > > > - /* > > - * This introduces a RCU read critical section, which could be > > - * disfunctional in cpu idle. Copy RCU_NONIDLE code to let RCU know > > - * this. > > - */ > > - rcu_irq_enter_irqson(); > > rcu_read_lock(); > > ret = raw_notifier_call_chain(&cpu_pm_notifier.chain, event, NULL); > > rcu_read_unlock(); > > - rcu_irq_exit_irqson(); > > To make this easier to debug, is it worth adding an assertion that RCU is > watching here? e.g. > > RCU_LOCKDEP_WARN(!rcu_is_watching(), > "cpu_pm_notify() used illegally from EQS"); > My understanding is that rcu_read_lock() implies something along those lines when PROVE_RCU.
On Tue, Jun 14, 2022 at 06:42:14PM +0200, Peter Zijlstra wrote: > On Tue, Jun 14, 2022 at 05:13:16PM +0100, Mark Rutland wrote: > > On Wed, Jun 08, 2022 at 04:27:38PM +0200, Peter Zijlstra wrote: > > > All callers should still have RCU enabled. > > > > IIUC with that true we should be able to drop the RCU_NONIDLE() from > > drivers/perf/arm_pmu.c, as we only needed that for an invocation via a pm > > notifier. > > > > I should be able to give that a spin on some hardware. > > > > > > > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > > > --- > > > kernel/cpu_pm.c | 9 --------- > > > 1 file changed, 9 deletions(-) > > > > > > --- a/kernel/cpu_pm.c > > > +++ b/kernel/cpu_pm.c > > > @@ -30,16 +30,9 @@ static int cpu_pm_notify(enum cpu_pm_eve > > > { > > > int ret; > > > > > > - /* > > > - * This introduces a RCU read critical section, which could be > > > - * disfunctional in cpu idle. Copy RCU_NONIDLE code to let RCU know > > > - * this. > > > - */ > > > - rcu_irq_enter_irqson(); > > > rcu_read_lock(); > > > ret = raw_notifier_call_chain(&cpu_pm_notifier.chain, event, NULL); > > > rcu_read_unlock(); > > > - rcu_irq_exit_irqson(); > > > > To make this easier to debug, is it worth adding an assertion that RCU is > > watching here? e.g. > > > > RCU_LOCKDEP_WARN(!rcu_is_watching(), > > "cpu_pm_notify() used illegally from EQS"); > > > > My understanding is that rcu_read_lock() implies something along those > lines when PROVE_RCU. Ah, duh. Given that: Acked-by: Mark Rutland <mark.rutland@arm.com> Mark.
--- a/kernel/cpu_pm.c +++ b/kernel/cpu_pm.c @@ -30,16 +30,9 @@ static int cpu_pm_notify(enum cpu_pm_eve { int ret; - /* - * This introduces a RCU read critical section, which could be - * disfunctional in cpu idle. Copy RCU_NONIDLE code to let RCU know - * this. - */ - rcu_irq_enter_irqson(); rcu_read_lock(); ret = raw_notifier_call_chain(&cpu_pm_notifier.chain, event, NULL); rcu_read_unlock(); - rcu_irq_exit_irqson(); return notifier_to_errno(ret); } @@ -49,11 +42,9 @@ static int cpu_pm_notify_robust(enum cpu unsigned long flags; int ret; - rcu_irq_enter_irqson(); raw_spin_lock_irqsave(&cpu_pm_notifier.lock, flags); ret = raw_notifier_call_chain_robust(&cpu_pm_notifier.chain, event_up, event_down, NULL); raw_spin_unlock_irqrestore(&cpu_pm_notifier.lock, flags); - rcu_irq_exit_irqson(); return notifier_to_errno(ret); }
All callers should still have RCU enabled. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- kernel/cpu_pm.c | 9 --------- 1 file changed, 9 deletions(-)