Re: [PATCH 15/36] cpuidle,cpu_pm: Remove RCU fiddling from cpu_pm_{enter,exit}()
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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)
> > > ---
> > > 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(_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.
Re: [PATCH 15/36] cpuidle,cpu_pm: Remove RCU fiddling from cpu_pm_{enter,exit}()
arndb.de>, ulli.kr...@googlemail.com, vgu...@kernel.org,
linux-...@vger.kernel.org, j...@joshtriplett.org, rost...@goodmis.org,
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tsbog...@alpha.franken.de, linux-par...@vger.kernel.org, sudeep.ho...@arm.com,
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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)
> > ---
> > 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(_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.
Re: [PATCH 15/36] cpuidle,cpu_pm: Remove RCU fiddling from cpu_pm_{enter,exit}()
arndb.de>, ulli.kr...@googlemail.com, vgu...@kernel.org,
linux-...@vger.kernel.org, j...@joshtriplett.org, rost...@goodmis.org,
r...@vger.kernel.org, b...@alien8.de, bc...@quicinc.com,
tsbog...@alpha.franken.de, linux-par...@vger.kernel.org, sudeep.ho...@arm.com,
shawn...@kernel.org, da...@davemloft.net, dal...@libc.org, t...@atomide.com,
amakha...@vmware.com, bjorn.anders...@linaro.org, h...@zytor.com,
sparcli...@vger.kernel.org, linux-hexa...@vger.kernel.org,
linux-ri...@lists.infradead.org, anton.iva...@cambridgegreys.com,
jo...@southpole.se, yury.no...@gmail.com, rich...@nod.at, x...@kernel.org,
li...@armlinux.org.uk, mi...@redhat.com, a...@eecs.berkeley.edu,
paul...@kernel.org, h...@linux.ibm.com, stefan.kristians...@saunalahti.fi,
openr...@lists.librecores.org, paul.walms...@sifive.com,
linux-te...@vger.kernel.org, namhy...@kernel.org,
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mon...@monstr.eu, linux-m...@vger.kernel.org, pal...@dabbelt.com, anup@brainfa
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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)
> ---
> 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(_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(_pm_notifier.lock, flags);
> ret = raw_notifier_call_chain_robust(_pm_notifier.chain, event_up,
> event_down, NULL);
> raw_spin_unlock_irqrestore(_pm_notifier.lock, flags);
> - rcu_irq_exit_irqson();
... and likewise here?
Thanks,
Mark.
>
> return notifier_to_errno(ret);
> }
>
>
[PATCH 15/36] cpuidle,cpu_pm: Remove RCU fiddling from cpu_pm_{enter,exit}()
, Arnd Bergmann , ulli.kr...@googlemail.com, vgu...@kernel.org,
linux-...@vger.kernel.org, j...@joshtriplett.org, rost...@goodmis.org,
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tsbog...@alpha.franken.de, linux-par...@vger.kernel.org, sudeep.ho...@arm.com,
shawn...@kernel.org, da...@davemloft.net, dal...@libc.org, t...@atomide.com,
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All callers should still have RCU enabled.
Signed-off-by: Peter Zijlstra (Intel)
---
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(_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(_pm_notifier.lock, flags);
ret = raw_notifier_call_chain_robust(_pm_notifier.chain, event_up,
event_down, NULL);
raw_spin_unlock_irqrestore(_pm_notifier.lock, flags);
- rcu_irq_exit_irqson();
return notifier_to_errno(ret);
}
