[PATCH/RESEND] ARM: arch_timer: Silence debug preempt warnings

[PATCH/RESEND] ARM: arch_timer: Silence debug preempt warnings

[Stephen Boyd]

Hot-plugging with CONFIG_DEBUG_PREEMPT=y on a device with arm
architected timers causes a slew of "using smp_processor_id() in
preemptible" warnings:

  BUG: using smp_processor_id() in preemptible [00000000] code: sh/111
  caller is arch_timer_cpu_notify+0x14/0xc8

This happens because sometimes the cpu notifier,
arch_timer_cpu_notify(), is called in preemptible context and
other times in non-preemptible context but we use this_cpu_ptr()
to retrieve the clockevent in all cases. We're only going to
actually use the pointer in non-preemptible context though, so
push the this_cpu_ptr() access down into the cases to force the
checks to occur only in non-preemptible contexts.

Cc: John Stultz <john.stultz@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Mark Rutland <mark.rutland@arm.com>
Acked-by: Marc Zyngier <Marc.Zyngier@arm.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
---

Resending to arm-soc maintainers instead of timekeeping maintainers. Who
maintains this driver?

 drivers/clocksource/arm_arch_timer.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index d7ad425..a65a710 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -248,14 +248,16 @@ static void __cpuinit arch_timer_stop(struct clock_event_device *clk)
 static int __cpuinit arch_timer_cpu_notify(struct notifier_block *self,
 					   unsigned long action, void *hcpu)
 {
-	struct clock_event_device *evt = this_cpu_ptr(arch_timer_evt);
-
+	/*
+	 * Grab cpu pointer in each case to avoid spurious
+	 * preemptible warnings
+	 */
 	switch (action & ~CPU_TASKS_FROZEN) {
 	case CPU_STARTING:
-		arch_timer_setup(evt);
+		arch_timer_setup(this_cpu_ptr(arch_timer_evt));
 		break;
 	case CPU_DYING:
-		arch_timer_stop(evt);
+		arch_timer_stop(this_cpu_ptr(arch_timer_evt));
 		break;
 	}
 
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
hosted by The Linux Foundation

[PATCH/RESEND] ARM: arch_timer: Silence debug preempt warnings

[Stephen Boyd]

On 04/17/13 16:26, Stephen Boyd wrote:
> Hot-plugging with CONFIG_DEBUG_PREEMPT=y on a device with arm
> architected timers causes a slew of "using smp_processor_id() in
> preemptible" warnings:
>
>   BUG: using smp_processor_id() in preemptible [00000000] code: sh/111
>   caller is arch_timer_cpu_notify+0x14/0xc8
>
> This happens because sometimes the cpu notifier,
> arch_timer_cpu_notify(), is called in preemptible context and
> other times in non-preemptible context but we use this_cpu_ptr()
> to retrieve the clockevent in all cases. We're only going to
> actually use the pointer in non-preemptible context though, so
> push the this_cpu_ptr() access down into the cases to force the
> checks to occur only in non-preemptible contexts.
>
> Cc: John Stultz <john.stultz@linaro.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Acked-by: Marc Zyngier <Marc.Zyngier@arm.com>
> Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
> ---
>
> Resending to arm-soc maintainers instead of timekeeping maintainers. Who
> maintains this driver?

Ping.

>
>  drivers/clocksource/arm_arch_timer.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index d7ad425..a65a710 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -248,14 +248,16 @@ static void __cpuinit arch_timer_stop(struct clock_event_device *clk)
>  static int __cpuinit arch_timer_cpu_notify(struct notifier_block *self,
>  					   unsigned long action, void *hcpu)
>  {
> -	struct clock_event_device *evt = this_cpu_ptr(arch_timer_evt);
> -
> +	/*
> +	 * Grab cpu pointer in each case to avoid spurious
> +	 * preemptible warnings
> +	 */
>  	switch (action & ~CPU_TASKS_FROZEN) {
>  	case CPU_STARTING:
> -		arch_timer_setup(evt);
> +		arch_timer_setup(this_cpu_ptr(arch_timer_evt));
>  		break;
>  	case CPU_DYING:
> -		arch_timer_stop(evt);
> +		arch_timer_stop(this_cpu_ptr(arch_timer_evt));
>  		break;
>  	}
>  


-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
hosted by The Linux Foundation

[PATCH/RESEND] ARM: arch_timer: Silence debug preempt warnings

[Olof Johansson]

On Wed, Apr 17, 2013 at 04:26:18PM -0700, Stephen Boyd wrote:
> Hot-plugging with CONFIG_DEBUG_PREEMPT=y on a device with arm
> architected timers causes a slew of "using smp_processor_id() in
> preemptible" warnings:
> 
>   BUG: using smp_processor_id() in preemptible [00000000] code: sh/111
>   caller is arch_timer_cpu_notify+0x14/0xc8
> 
> This happens because sometimes the cpu notifier,
> arch_timer_cpu_notify(), is called in preemptible context and
> other times in non-preemptible context but we use this_cpu_ptr()
> to retrieve the clockevent in all cases. We're only going to
> actually use the pointer in non-preemptible context though, so
> push the this_cpu_ptr() access down into the cases to force the
> checks to occur only in non-preemptible contexts.
> 
> Cc: John Stultz <john.stultz@linaro.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Acked-by: Marc Zyngier <Marc.Zyngier@arm.com>
> Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
> ---
> 
> Resending to arm-soc maintainers instead of timekeeping maintainers. Who
> maintains this driver?

Subsystem is maintained by John and Thomas, but given the recent moves of ARM
drivers there (which mostly has been acked by them), we'll take the patch at
this time.

Applied on top of late/clksrc in arm-soc. Thanks.


-Olof