* [PATCH] ARM: imx6q: Fixup RCU usage for cpuidle
@ 2020-09-30 11:20 Ulf Hansson
2020-09-30 11:33 ` Peter Zijlstra
0 siblings, 1 reply; 3+ messages in thread
From: Ulf Hansson @ 2020-09-30 11:20 UTC (permalink / raw)
To: Shawn Guo, Dong Aisheng, Fabio Estevam, Sascha Hauer
Cc: Peter Zijlstra, Rafael J . Wysocki, Paul E . McKenney,
Daniel Lezcano, Anson Huang, Ulf Hansson, linux-pm,
linux-arm-kernel
The commit eb1f00237aca ("lockdep,trace: Expose tracepoints"), started to
expose us for tracepoints. For imx6q cpuidle, this leads to an RCU splat
according to below.
[6.870684] [<c0db7690>] (_raw_spin_lock) from [<c011f6a4>] (imx6q_enter_wait+0x18/0x9c)
[6.878846] [<c011f6a4>] (imx6q_enter_wait) from [<c09abfb0>] (cpuidle_enter_state+0x168/0x5e4)
To fix the problem, let's assign the corresponding idlestate->flags the
CPUIDLE_FLAG_RCU_IDLE bit, which enables us to call rcu_idle_enter|exit()
at the proper point.
Reported-by: Dong Aisheng <aisheng.dong@nxp.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
---
arch/arm/mach-imx/cpuidle-imx6q.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/arm/mach-imx/cpuidle-imx6q.c b/arch/arm/mach-imx/cpuidle-imx6q.c
index 24dd5bbe60e4..094337dc1bc7 100644
--- a/arch/arm/mach-imx/cpuidle-imx6q.c
+++ b/arch/arm/mach-imx/cpuidle-imx6q.c
@@ -24,7 +24,9 @@ static int imx6q_enter_wait(struct cpuidle_device *dev,
imx6_set_lpm(WAIT_UNCLOCKED);
raw_spin_unlock(&cpuidle_lock);
+ rcu_idle_enter();
cpu_do_idle();
+ rcu_idle_exit();
raw_spin_lock(&cpuidle_lock);
if (num_idle_cpus-- == num_online_cpus())
@@ -44,7 +46,7 @@ static struct cpuidle_driver imx6q_cpuidle_driver = {
{
.exit_latency = 50,
.target_residency = 75,
- .flags = CPUIDLE_FLAG_TIMER_STOP,
+ .flags = CPUIDLE_FLAG_TIMER_STOP | CPUIDLE_FLAG_RCU_IDLE,
.enter = imx6q_enter_wait,
.name = "WAIT",
.desc = "Clock off",
--
2.25.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] ARM: imx6q: Fixup RCU usage for cpuidle
2020-09-30 11:20 [PATCH] ARM: imx6q: Fixup RCU usage for cpuidle Ulf Hansson
@ 2020-09-30 11:33 ` Peter Zijlstra
2020-09-30 15:44 ` Rafael J. Wysocki
0 siblings, 1 reply; 3+ messages in thread
From: Peter Zijlstra @ 2020-09-30 11:33 UTC (permalink / raw)
To: Ulf Hansson
Cc: Shawn Guo, Dong Aisheng, Fabio Estevam, Sascha Hauer,
Rafael J . Wysocki, Paul E . McKenney, Daniel Lezcano,
Anson Huang, linux-pm, linux-arm-kernel
On Wed, Sep 30, 2020 at 01:20:23PM +0200, Ulf Hansson wrote:
> The commit eb1f00237aca ("lockdep,trace: Expose tracepoints"), started to
> expose us for tracepoints. For imx6q cpuidle, this leads to an RCU splat
> according to below.
>
> [6.870684] [<c0db7690>] (_raw_spin_lock) from [<c011f6a4>] (imx6q_enter_wait+0x18/0x9c)
> [6.878846] [<c011f6a4>] (imx6q_enter_wait) from [<c09abfb0>] (cpuidle_enter_state+0x168/0x5e4)
>
> To fix the problem, let's assign the corresponding idlestate->flags the
> CPUIDLE_FLAG_RCU_IDLE bit, which enables us to call rcu_idle_enter|exit()
> at the proper point.
>
> Reported-by: Dong Aisheng <aisheng.dong@nxp.com>
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Yep, that looks about right.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> arch/arm/mach-imx/cpuidle-imx6q.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/mach-imx/cpuidle-imx6q.c b/arch/arm/mach-imx/cpuidle-imx6q.c
> index 24dd5bbe60e4..094337dc1bc7 100644
> --- a/arch/arm/mach-imx/cpuidle-imx6q.c
> +++ b/arch/arm/mach-imx/cpuidle-imx6q.c
> @@ -24,7 +24,9 @@ static int imx6q_enter_wait(struct cpuidle_device *dev,
> imx6_set_lpm(WAIT_UNCLOCKED);
> raw_spin_unlock(&cpuidle_lock);
>
> + rcu_idle_enter();
> cpu_do_idle();
> + rcu_idle_exit();
>
> raw_spin_lock(&cpuidle_lock);
> if (num_idle_cpus-- == num_online_cpus())
> @@ -44,7 +46,7 @@ static struct cpuidle_driver imx6q_cpuidle_driver = {
> {
> .exit_latency = 50,
> .target_residency = 75,
> - .flags = CPUIDLE_FLAG_TIMER_STOP,
> + .flags = CPUIDLE_FLAG_TIMER_STOP | CPUIDLE_FLAG_RCU_IDLE,
> .enter = imx6q_enter_wait,
> .name = "WAIT",
> .desc = "Clock off",
> --
> 2.25.1
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] ARM: imx6q: Fixup RCU usage for cpuidle
2020-09-30 11:33 ` Peter Zijlstra
@ 2020-09-30 15:44 ` Rafael J. Wysocki
0 siblings, 0 replies; 3+ messages in thread
From: Rafael J. Wysocki @ 2020-09-30 15:44 UTC (permalink / raw)
To: Peter Zijlstra, Ulf Hansson
Cc: Shawn Guo, Dong Aisheng, Fabio Estevam, Sascha Hauer,
Rafael J . Wysocki, Paul E . McKenney, Daniel Lezcano,
Anson Huang, Linux PM, Linux ARM
On Wed, Sep 30, 2020 at 1:33 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Wed, Sep 30, 2020 at 01:20:23PM +0200, Ulf Hansson wrote:
> > The commit eb1f00237aca ("lockdep,trace: Expose tracepoints"), started to
> > expose us for tracepoints. For imx6q cpuidle, this leads to an RCU splat
> > according to below.
> >
> > [6.870684] [<c0db7690>] (_raw_spin_lock) from [<c011f6a4>] (imx6q_enter_wait+0x18/0x9c)
> > [6.878846] [<c011f6a4>] (imx6q_enter_wait) from [<c09abfb0>] (cpuidle_enter_state+0x168/0x5e4)
> >
> > To fix the problem, let's assign the corresponding idlestate->flags the
> > CPUIDLE_FLAG_RCU_IDLE bit, which enables us to call rcu_idle_enter|exit()
> > at the proper point.
> >
> > Reported-by: Dong Aisheng <aisheng.dong@nxp.com>
> > Suggested-by: Peter Zijlstra <peterz@infradead.org>
> > Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
>
> Yep, that looks about right.
>
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>
> > ---
> > arch/arm/mach-imx/cpuidle-imx6q.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm/mach-imx/cpuidle-imx6q.c b/arch/arm/mach-imx/cpuidle-imx6q.c
> > index 24dd5bbe60e4..094337dc1bc7 100644
> > --- a/arch/arm/mach-imx/cpuidle-imx6q.c
> > +++ b/arch/arm/mach-imx/cpuidle-imx6q.c
> > @@ -24,7 +24,9 @@ static int imx6q_enter_wait(struct cpuidle_device *dev,
> > imx6_set_lpm(WAIT_UNCLOCKED);
> > raw_spin_unlock(&cpuidle_lock);
> >
> > + rcu_idle_enter();
> > cpu_do_idle();
> > + rcu_idle_exit();
> >
> > raw_spin_lock(&cpuidle_lock);
> > if (num_idle_cpus-- == num_online_cpus())
> > @@ -44,7 +46,7 @@ static struct cpuidle_driver imx6q_cpuidle_driver = {
> > {
> > .exit_latency = 50,
> > .target_residency = 75,
> > - .flags = CPUIDLE_FLAG_TIMER_STOP,
> > + .flags = CPUIDLE_FLAG_TIMER_STOP | CPUIDLE_FLAG_RCU_IDLE,
> > .enter = imx6q_enter_wait,
> > .name = "WAIT",
> > .desc = "Clock off",
> > --
Applied as 5.9-rc8 material, thanks!
^ permalink raw reply [flat|nested] 3+ messages in thread
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2020-09-30 11:20 [PATCH] ARM: imx6q: Fixup RCU usage for cpuidle Ulf Hansson
2020-09-30 11:33 ` Peter Zijlstra
2020-09-30 15:44 ` Rafael J. Wysocki
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