On Wed, Aug 26, 2020 at 09:18:26PM -0400, Joel Fernandes wrote:
> On Fri, Aug 21, 2020 at 10:47:41AM +0200, Peter Zijlstra wrote:
> > Lots of things take locks, due to a wee bug, rcu_lockdep didn't notice
> > that the locking tracepoints were using RCU.
> >
> > Push rcu_idle_{enter,exit}() as deep as possible into the idle paths,
> > this also resolves a lot of _rcuidle()/RCU_NONIDLE() usage.
> >
> > Specifically, sched_clock_idle_wakeup_event() will use ktime which
> > will use seqlocks which will tickle lockdep, and
> > stop_critical_timings() uses lock.
>
> I was wondering if those tracepoints should just use _rcuidle variant of the
> trace call. But that's a terrible idea considering that would add unwanted
> overhead I think.
>
> Reviewed-by: Joel Fernandes (Google) <[email protected]>
BTW, if tracepoint is converted to use RCU-trace flavor, then these kinds of
issues go away, no? That RCU flavor is always watching.
thanks,
- Joel
>
> thanks,
>
> - Joel
>
> >
> > Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
> > Reviewed-by: Steven Rostedt (VMware) <[email protected]>
> > Tested-by: Marco Elver <[email protected]>
> > ---
> > drivers/cpuidle/cpuidle.c | 12 ++++++++----
> > kernel/sched/idle.c | 22 ++++++++--------------
> > 2 files changed, 16 insertions(+), 18 deletions(-)
> >
> > --- a/drivers/cpuidle/cpuidle.c
> > +++ b/drivers/cpuidle/cpuidle.c
> > @@ -145,13 +145,14 @@ static void enter_s2idle_proper(struct c
> > * executing it contains RCU usage regarded as invalid in the idle
> > * context, so tell RCU about that.
> > */
> > - RCU_NONIDLE(tick_freeze());
> > + tick_freeze();
> > /*
> > * The state used here cannot be a "coupled" one, because the "coupled"
> > * cpuidle mechanism enables interrupts and doing that with timekeeping
> > * suspended is generally unsafe.
> > */
> > stop_critical_timings();
> > + rcu_idle_enter();
> > drv->states[index].enter_s2idle(dev, drv, index);
> > if (WARN_ON_ONCE(!irqs_disabled()))
> > local_irq_disable();
> > @@ -160,7 +161,8 @@ static void enter_s2idle_proper(struct c
> > * first CPU executing it calls functions containing RCU read-side
> > * critical sections, so tell RCU about that.
> > */
> > - RCU_NONIDLE(tick_unfreeze());
> > + rcu_idle_exit();
> > + tick_unfreeze();
> > start_critical_timings();
> >
> > time_end = ns_to_ktime(local_clock());
> > @@ -229,16 +231,18 @@ int cpuidle_enter_state(struct cpuidle_d
> > /* Take note of the planned idle state. */
> > sched_idle_set_state(target_state);
> >
> > - trace_cpu_idle_rcuidle(index, dev->cpu);
> > + trace_cpu_idle(index, dev->cpu);
> > time_start = ns_to_ktime(local_clock());
> >
> > stop_critical_timings();
> > + rcu_idle_enter();
> > entered_state = target_state->enter(dev, drv, index);
> > + rcu_idle_exit();
> > start_critical_timings();
> >
> > sched_clock_idle_wakeup_event();
> > time_end = ns_to_ktime(local_clock());
> > - trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu);
> > + trace_cpu_idle(PWR_EVENT_EXIT, dev->cpu);
> >
> > /* The cpu is no longer idle or about to enter idle. */
> > sched_idle_set_state(NULL);
> > --- a/kernel/sched/idle.c
> > +++ b/kernel/sched/idle.c
> > @@ -54,17 +54,18 @@ __setup("hlt", cpu_idle_nopoll_setup);
> >
> > static noinline int __cpuidle cpu_idle_poll(void)
> > {
> > + trace_cpu_idle(0, smp_processor_id());
> > + stop_critical_timings();
> > rcu_idle_enter();
> > - trace_cpu_idle_rcuidle(0, smp_processor_id());
> > local_irq_enable();
> > - stop_critical_timings();
> >
> > while (!tif_need_resched() &&
> > - (cpu_idle_force_poll || tick_check_broadcast_expired()))
> > + (cpu_idle_force_poll || tick_check_broadcast_expired()))
> > cpu_relax();
> > - start_critical_timings();
> > - trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
> > +
> > rcu_idle_exit();
> > + start_critical_timings();
> > + trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
> >
> > return 1;
> > }
> > @@ -91,7 +92,9 @@ void __cpuidle default_idle_call(void)
> > local_irq_enable();
> > } else {
> > stop_critical_timings();
> > + rcu_idle_enter();
> > arch_cpu_idle();
> > + rcu_idle_exit();
> > start_critical_timings();
> > }
> > }
> > @@ -158,7 +161,6 @@ static void cpuidle_idle_call(void)
> >
> > if (cpuidle_not_available(drv, dev)) {
> > tick_nohz_idle_stop_tick();
> > - rcu_idle_enter();
> >
> > default_idle_call();
> > goto exit_idle;
> > @@ -178,21 +180,17 @@ static void cpuidle_idle_call(void)
> > u64 max_latency_ns;
> >
> > if (idle_should_enter_s2idle()) {
> > - rcu_idle_enter();
> >
> > entered_state = call_cpuidle_s2idle(drv, dev);
> > if (entered_state > 0)
> > goto exit_idle;
> >
> > - rcu_idle_exit();
> > -
> > max_latency_ns = U64_MAX;
> > } else {
> > max_latency_ns = dev->forced_idle_latency_limit_ns;
> > }
> >
> > tick_nohz_idle_stop_tick();
> > - rcu_idle_enter();
> >
> > next_state = cpuidle_find_deepest_state(drv, dev,
> > max_latency_ns);
> > call_cpuidle(drv, dev, next_state);
> > @@ -209,8 +207,6 @@ static void cpuidle_idle_call(void)
> > else
> > tick_nohz_idle_retain_tick();
> >
> > - rcu_idle_enter();
> > -
> > entered_state = call_cpuidle(drv, dev, next_state);
> > /*
> > * Give the governor an opportunity to reflect on the outcome
> > @@ -226,8 +222,6 @@ static void cpuidle_idle_call(void)
> > */
> > if (WARN_ON_ONCE(irqs_disabled()))
> > local_irq_enable();
> > -
> > - rcu_idle_exit();
> > }
> >
> > /*
> >
> >
