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Date: Tue, 1 Sep 2020 09:44:17 -0600
From: Lina Iyer <ilina@...eaurora.org>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
Naresh Kamboju <naresh.kamboju@...aro.org>, paulmck@...nel.org,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
Saravana Kannan <saravanak@...gle.com>,
open list <linux-kernel@...r.kernel.org>,
linux-mmc <linux-mmc@...r.kernel.org>,
lkft-triage@...ts.linaro.org, rcu@...r.kernel.org,
Linux PM <linux-pm@...r.kernel.org>,
Anders Roxell <anders.roxell@...aro.org>,
Arnd Bergmann <arnd@...db.de>,
Rajendra Nayak <rnayak@...eaurora.org>,
John Stultz <john.stultz@...aro.org>,
Stephen Boyd <sboyd@...nel.org>,
Lars Povlsen <lars.povlsen@...rochip.com>,
madhuparnabhowmik10@...il.com,
Viresh Kumar <viresh.kumar@...aro.org>,
Vincent Guittot <vincent.guittot@...aro.org>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: WARNING: suspicious RCU usage - sdhci-pltfm: SDHCI platform and
OF driver helper
Hi Ulf,
On Tue, Sep 01 2020 at 06:41 -0600, Ulf Hansson wrote:
>On Tue, 1 Sep 2020 at 14:35, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>>
>> On Tue, 1 Sep 2020 at 12:42, <peterz@...radead.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@...aro.org> wrote:
>> > > > On Mon, 31 Aug 2020 at 21:44, Paul E. McKenney <paulmck@...nel.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.
>> > > >
I think this would be nice. This should also cover the case, where PM domain
power off notification callbacks call trace function internally. Right?
--Lina
>> > > > 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
>
[1]. https://lkml.org/lkml/2020/8/26/81
>>
>> >
>> > 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;
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