[PATCH] cpuidle: psci: Fix suspicious RCU usage

[Ulf Hansson]

On Fri, 4 Sep 2020 at 16:13, Paul E. McKenney <paulmck at kernel.org> wrote:
>
> On Fri, Sep 04, 2020 at 08:47:05AM +0200, Ulf Hansson wrote:
> > The commit eb1f00237aca ("lockdep,trace: Expose tracepoints"), started to
> > expose us for tracepoints. This lead to the following RCU splat on an ARM64
> > Qcom board.
> >
> > [    5.529634] WARNING: suspicious RCU usage
> > [    5.537307] sdhci-pltfm: SDHCI platform and OF driver helper
> > [    5.541092] 5.9.0-rc3 #86 Not tainted
> > [    5.541098] -----------------------------
> > [    5.541105] ../include/trace/events/lock.h:37 suspicious rcu_dereference_check() usage!
> > [    5.541110]
> > [    5.541110] other info that might help us debug this:
> > [    5.541110]
> > [    5.541116]
> > [    5.541116] rcu_scheduler_active = 2, debug_locks = 1
> > [    5.541122] RCU used illegally from extended quiescent state!
> > [    5.541129] no locks held by swapper/0/0.
> > [    5.541134]
> > [    5.541134] stack backtrace:
> > [    5.541143] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.9.0-rc3 #86
> > [    5.541149] Hardware name: Qualcomm Technologies, Inc. APQ 8016 SBC (DT)
> > [    5.541157] Call trace:
> > [    5.568185] sdhci_msm 7864900.sdhci: Got CD GPIO
> > [    5.574186]  dump_backtrace+0x0/0x1c8
> > [    5.574206]  show_stack+0x14/0x20
> > [    5.574229]  dump_stack+0xe8/0x154
> > [    5.574250]  lockdep_rcu_suspicious+0xd4/0xf8
> > [    5.574269]  lock_acquire+0x3f0/0x460
> > [    5.574292]  _raw_spin_lock_irqsave+0x80/0xb0
> > [    5.574314]  __pm_runtime_suspend+0x4c/0x188
> > [    5.574341]  psci_enter_domain_idle_state+0x40/0xa0
> > [    5.574362]  cpuidle_enter_state+0xc0/0x610
> > [    5.646487]  cpuidle_enter+0x38/0x50
> > [    5.650651]  call_cpuidle+0x18/0x40
> > [    5.654467]  do_idle+0x228/0x278
> > [    5.657678]  cpu_startup_entry+0x24/0x70
> > [    5.661153]  rest_init+0x1a4/0x278
> > [    5.665061]  arch_call_rest_init+0xc/0x14
> > [    5.668272]  start_kernel+0x508/0x540
> >
> > Following the path in pm_runtime_put_sync_suspend() from
> > psci_enter_domain_idle_state(), it seems like we end up using the RCU.
> > Therefore, let's simply silence the splat by informing the RCU about it
> > with RCU_NONIDLE.
> >
> > Note that, this is a temporary solution. Instead we should strive to avoid
> > using RCU_NONIDLE (and similar), but rather push rcu_idle_enter|exit()
> > further down, closer to the arch specific code. However, as the CPU PM
> > notifiers are also using the RCU, additional rework is needed.
> >
> > Reported-by: Naresh Kamboju <naresh.kamboju at linaro.org>
> > Signed-off-by: Ulf Hansson <ulf.hansson at linaro.org>
>
> Acked-by: Paul E. McKenney <paulmck at kernel.org>

Peter, Rafael,

Is $subject patch okay as the short term solution? If so, I can
continue to look at the CPU PM notifiers, etc.

Kind regards
Uffe

>
> > ---
> >  drivers/cpuidle/cpuidle-psci.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c
> > index 74463841805f..d928b37718bd 100644
> > --- a/drivers/cpuidle/cpuidle-psci.c
> > +++ b/drivers/cpuidle/cpuidle-psci.c
> > @@ -66,7 +66,7 @@ static int psci_enter_domain_idle_state(struct cpuidle_device *dev,
> >               return -1;
> >
> >       /* Do runtime PM to manage a hierarchical CPU toplogy. */
> > -     pm_runtime_put_sync_suspend(pd_dev);
> > +     RCU_NONIDLE(pm_runtime_put_sync_suspend(pd_dev));
> >
> >       state = psci_get_domain_state();
> >       if (!state)
> > @@ -74,7 +74,7 @@ static int psci_enter_domain_idle_state(struct cpuidle_device *dev,
> >
> >       ret = psci_cpu_suspend_enter(state) ? -1 : idx;
> >
> > -     pm_runtime_get_sync(pd_dev);
> > +     RCU_NONIDLE(pm_runtime_get_sync(pd_dev));
> >
> >       cpu_pm_exit();
> >
> > --
> > 2.25.1
> >