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From:   Ulf Hansson <ulf.hansson@linaro.org>
Date:   Tue, 1 Sep 2020 14:40:33 +0200
Message-ID: <CAPDyKFrv+DTF8=twZZk_tenB-sLg6H-CFn9HVDVA5S2kK2=U5Q@mail.gmail.com>
Subject: Re: WARNING: suspicious RCU usage - sdhci-pltfm: SDHCI platform and
 OF driver helper
To:     Peter Zijlstra <peterz@infradead.org>,
        Naresh Kamboju <naresh.kamboju@linaro.org>
Cc:     paulmck@kernel.org, "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Saravana Kannan <saravanak@google.com>,
        open list <linux-kernel@vger.kernel.org>,
        linux-mmc <linux-mmc@vger.kernel.org>,
        lkft-triage@lists.linaro.org, rcu@vger.kernel.org,
        Linux PM <linux-pm@vger.kernel.org>,
        Anders Roxell <anders.roxell@linaro.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Rajendra Nayak <rnayak@codeaurora.org>,
        John Stultz <john.stultz@linaro.org>,
        Stephen Boyd <sboyd@kernel.org>,
        Lars Povlsen <lars.povlsen@microchip.com>,
        madhuparnabhowmik10@gmail.com,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Lina Iyer <ilina@codeaurora.org>,
        Thomas Gleixner <tglx@linutronix.de>
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On Tue, 1 Sep 2020 at 14:35, Ulf Hansson <ulf.hansson@linaro.org> wrote:
>
> On Tue, 1 Sep 2020 at 12:42, <peterz@infradead.org> wrote:
> >
> > On Tue, Sep 01, 2020 at 08:50:57AM +0200, Ulf Hansson wrote:
> > > On Tue, 1 Sep 2020 at 08:46, Ulf Hansson <ulf.hansson@linaro.org> wrote:
> > > > On Mon, 31 Aug 2020 at 21:44, Paul E. McKenney <paulmck@kernel.org> wrote:
> >
> > > > > > [    5.308588] =============================
> > > > > > [    5.308593] WARNING: suspicious RCU usage
> > > > > > [    5.316628] sdhci-pltfm: SDHCI platform and OF driver helper
> > > > > > [    5.320052] 5.9.0-rc3 #1 Not tainted
> > > > > > [    5.320057] -----------------------------
> > > > > > [    5.320063] /usr/src/kernel/include/trace/events/lock.h:37 suspicious rcu_dereference_check() usage!
> > > > > > [    5.320068]
> > > > > > [    5.320068] other info that might help us debug this:
> > > > > > [    5.320068]
> > > > > > [    5.320074]
> > > > > > [    5.320074] rcu_scheduler_active = 2, debug_locks = 1
> > > > > > [    5.320078] RCU used illegally from extended quiescent state!
> > > > > > [    5.320084] no locks held by swapper/0/0.
> > > > > > [    5.320089]
> > > > > > [    5.320089] stack backtrace:
> > > > > > [    5.320098] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.9.0-rc3 #1
> > > > > > [    5.346354] sdhci_msm 7864900.sdhci: Got CD GPIO
> > > > > > [    5.346446] Hardware name: Qualcomm Technologies, Inc. APQ 8016 SBC (DT)
> > > > > > [    5.346452] Call trace:
> > > > > > [    5.346463]  dump_backtrace+0x0/0x1f8
> > > > > > [    5.346471]  show_stack+0x2c/0x38
> > > > > > [    5.346480]  dump_stack+0xec/0x15c
> > > > > > [    5.346490]  lockdep_rcu_suspicious+0xd4/0xf8
> > > > > > [    5.346499]  lock_acquire+0x3d0/0x440
> > > > > > [    5.346510]  _raw_spin_lock_irqsave+0x80/0xb0
> > > > > > [    5.413118]  __pm_runtime_suspend+0x34/0x1d0
> > > > > > [    5.417457]  psci_enter_domain_idle_state+0x4c/0xb0
> > > > > > [    5.421795]  cpuidle_enter_state+0xc8/0x610
> > > > > > [    5.426392]  cpuidle_enter+0x3c/0x50
> > > > > > [    5.430561]  call_cpuidle+0x44/0x80
> > > > > > [    5.434378]  do_idle+0x240/0x2a0
> >
> > > > > Note also that Peter Zijlstra (CCed) is working to shrink the portion
> > > > > of the idle loop that RCU ignores.  Not sure that it covers your
> > > > > case, but it is worth checking.
> >
> > Right, so I think I 'caused' this by making the lock tracepoints
> > visible. That is, the error always existed, now we actually warn about
> > it.
> >
> > > > Thanks for letting me know. Let's see what Peter thinks about this then.
> > > >
> > > > Apologize for my ignorance, but from a cpuidle point of view, what
> > > > does it mean using RCU_NONIDLE()? I guess we should avoid RCU_NONIDLE
> > > > on bigger code paths?
> > > >
> > > > I could add RCU_NONIDLE for the calls to pm_runtime_put_sync_suspend()
> > > > and pm_runtime_get_sync() in psci_enter_domain_idle_state(). Perhaps
> > > > that's the easiest approach, at least to start with.
> > > >
> > > > Or do you have any other ideas?
> >
> > So IMO trace_*_rcuidle() and RCU_NONIDLE() are bugs, they just mean we
> > got the ordering wrong and are papering over it. That said, that's been
> > the modus operandi for a while now, just make it shut up and don't think
> > about it :-/
> >
> > That said; I pushed the rcu_idle_enter() about as deep as it goes into
> > generic code in commit 1098582a0f6c ("sched,idle,rcu: Push rcu_idle
> > deeper into the idle path")
>
> Aha, that commit should fix this problem, I think. Looks like that
> commit was sent as a fix and included in the recent v5.9-rc3.
>
> Naresh, can you try with the above commit?

Ah, just realized that I misread the patch. It doesn't fix it.

We would still need a RCU_NONIDLE() in psci_enter_domain_idle_state()
- or something along the lines of what you suggest below.

Apologies for the noise.

Kind regards
Uffe

>
> >
> > I suppose the next step is pushing it into individual driver when
> > needed, something like the below perhaps. I realize the coupled idle
> > state stuff is more complicated that most, but it's also not an area
> > I've looked at in detail, so perhaps I've just made a bigger mess, but
> > it ought to give you enough to get going I think.
>
> These aren't coupled states. Instead, in cpuidle-psci, we are using PM
> domains through genpd and runtime PM to manage "shared idle states"
> between CPUs.
>
> Kind regards
> Uffe
>
> >
> > Rafael?
> >
> > ---
> > diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c
> > index 74463841805f..617bbef316e6 100644
> > --- a/drivers/cpuidle/cpuidle-psci.c
> > +++ b/drivers/cpuidle/cpuidle-psci.c
> > @@ -49,6 +49,9 @@ static inline u32 psci_get_domain_state(void)
> >
> >  static inline int psci_enter_state(int idx, u32 state)
> >  {
> > +       /*
> > +        * XXX push rcu_idle_enter into the coupled code
> > +        */
> >         return CPU_PM_CPU_IDLE_ENTER_PARAM(psci_cpu_suspend_enter, idx, state);
> >  }
> >
> > @@ -72,7 +75,9 @@ static int psci_enter_domain_idle_state(struct cpuidle_device *dev,
> >         if (!state)
> >                 state = states[idx];
> >
> > +       rcu_idle_enter();
> >         ret = psci_cpu_suspend_enter(state) ? -1 : idx;
> > +       rcu_idle_exit();
> >
> >         pm_runtime_get_sync(pd_dev);
> >
> > @@ -125,8 +130,13 @@ static int psci_enter_idle_state(struct cpuidle_device *dev,
> >                                 struct cpuidle_driver *drv, int idx)
> >  {
> >         u32 *state = __this_cpu_read(psci_cpuidle_data.psci_states);
> > +       int ret;
> >
> > -       return psci_enter_state(idx, state[idx]);
> > +       rcu_idle_enter();
> > +       ret = psci_enter_state(idx, state[idx]);
> > +       rcu_idle_exit();
> > +
> > +       return ret;
> >  }
> >
> >  static const struct of_device_id psci_idle_state_match[] = {
> > @@ -170,6 +180,7 @@ static int psci_dt_cpu_init_topology(struct cpuidle_driver *drv,
> >          * deeper states.
> >          */
> >         drv->states[state_count - 1].enter = psci_enter_domain_idle_state;
> > +       drv->states[state_count - 1].flags = CPUIDLE_FLAG_RCU_IDLE;
> >         psci_cpuidle_use_cpuhp = true;
> >
> >         return 0;
> > @@ -285,6 +296,7 @@ static int psci_idle_init_cpu(struct device *dev, int cpu)
> >          * state index 0.
> >          */
> >         drv->states[0].enter = psci_enter_idle_state;
> > +       drv->states[0].flags = CPUIDLE_FLAG_RCU_IDLE;
> >         drv->states[0].exit_latency = 1;
> >         drv->states[0].target_residency = 1;
> >         drv->states[0].power_usage = UINT_MAX;
> > diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> > index 04becd70cc41..3dbac3bb761b 100644
> > --- a/drivers/cpuidle/cpuidle.c
> > +++ b/drivers/cpuidle/cpuidle.c
> > @@ -239,9 +239,11 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
> >         time_start = ns_to_ktime(local_clock());
> >
> >         stop_critical_timings();
> > -       rcu_idle_enter();
> > +       if (!(target_state->flags & CPUIDLE_FLAG_RCU_IDLE))
> > +               rcu_idle_enter();
> >         entered_state = target_state->enter(dev, drv, index);
> > -       rcu_idle_exit();
> > +       if (!(target_state->flags & CPUIDLE_FLAG_RCU_IDLE))
> > +               rcu_idle_exit();
> >         start_critical_timings();
> >
> >         sched_clock_idle_wakeup_event();
> > diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
> > index 75895e6363b8..47f686131a54 100644
> > --- a/include/linux/cpuidle.h
> > +++ b/include/linux/cpuidle.h
> > @@ -82,6 +82,7 @@ struct cpuidle_state {
> >  #define CPUIDLE_FLAG_UNUSABLE          BIT(3) /* avoid using this state */
> >  #define CPUIDLE_FLAG_OFF               BIT(4) /* disable this state by default */
> >  #define CPUIDLE_FLAG_TLB_FLUSHED       BIT(5) /* idle-state flushes TLBs */
> > +#define CPUIDLE_FLAG_RCU_IDLE          BIT(6) /* driver will do RCU-idle */
> >
> >  struct cpuidle_device_kobj;
> >  struct cpuidle_state_kobj;