[PATCH 2/4] ARM: perf: clear overflow flag when disabling counter on ARMv7 PMU

[Ming Lei]

On Thu, Feb 23, 2012 at 11:58 PM, Will Deacon <will.deacon at arm.com> wrote:
> When disabling a counter on an ARMv7 PMU, we should also clear the
> overflow flag in case an overflow occurred whilst stopping the counter.
> This prevents a spurious overflow being picked up later and leading to
> either false accounting or a NULL dereference.
>
> Signed-off-by: Will Deacon <will.deacon at arm.com>

Reported-by: Ming Lei <tom.leiming at gmail.com>

> ---
>  arch/arm/kernel/perf_event_v7.c |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
>
> diff --git a/arch/arm/kernel/perf_event_v7.c b/arch/arm/kernel/perf_event_v7.c
> index 6f48861..050cc8b 100644
> --- a/arch/arm/kernel/perf_event_v7.c
> +++ b/arch/arm/kernel/perf_event_v7.c
> @@ -809,6 +809,11 @@ static inline int armv7_pmnc_disable_intens(int idx)
>
>        counter = ARMV7_IDX_TO_COUNTER(idx);
>        asm volatile("mcr p15, 0, %0, c9, c14, 2" : : "r" (BIT(counter)));
> +       isb();
> +       /* Clear the overflow flag in case an interrupt is pending. */
> +       asm volatile("mcr p15, 0, %0, c9, c12, 3" : : "r" (BIT(counter)));
> +       isb();
> +
>        return idx;
>  }
>
> --
> 1.7.4.1
>
>
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-- 
Ming Lei