R Sricharan <r.sricharan@xxxxxx> writes:
> From: Colin Cross <ccross@xxxxxxxxxxx>
>
> read_persistent_clock uses a global variable, use a spinlock to
> ensure non-atomic updates to the variable don't overlap and cause
> time to move backwards.
>
> Signed-off-by: Colin Cross <ccross@xxxxxxxxxxx>
> Signed-off-by: R Sricharan <r.sricharan@xxxxxx>
Acked-by: Kevin Hilman <khilman@xxxxxx>
Tony, this should probably be queued up for v3.7-rc and flagged for stable.
Thanks,
Kevin
> ---
> [V2] Added signed-off-by and looped in "linux-arm-kernel" list
>
> arch/arm/plat-omap/counter_32k.c | 21 ++++++++++++++-------
> 1 file changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm/plat-omap/counter_32k.c b/arch/arm/plat-omap/counter_32k.c
> index dbf1e03..2bc51fb 100644
> --- a/arch/arm/plat-omap/counter_32k.c
> +++ b/arch/arm/plat-omap/counter_32k.c
> @@ -55,22 +55,29 @@ static u32 notrace omap_32k_read_sched_clock(void)
> * nsecs and adds to a monotonically increasing timespec.
> */
> static struct timespec persistent_ts;
> -static cycles_t cycles, last_cycles;
> +static cycles_t cycles;
> static unsigned int persistent_mult, persistent_shift;
> +static DEFINE_SPINLOCK(read_persistent_clock_lock);
> +
> static void omap_read_persistent_clock(struct timespec *ts)
> {
> unsigned long long nsecs;
> - cycles_t delta;
> - struct timespec *tsp = &persistent_ts;
> + cycles_t last_cycles;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&read_persistent_clock_lock, flags);
>
> last_cycles = cycles;
> cycles = sync32k_cnt_reg ? __raw_readl(sync32k_cnt_reg) : 0;
> - delta = cycles - last_cycles;
>
> - nsecs = clocksource_cyc2ns(delta, persistent_mult, persistent_shift);
> + nsecs = clocksource_cyc2ns(cycles - last_cycles,
> + persistent_mult, persistent_shift);
> +
> + timespec_add_ns(&persistent_ts, nsecs);
> +
> + *ts = persistent_ts;
>
> - timespec_add_ns(tsp, nsecs);
> - *ts = *tsp;
> + spin_unlock_irqrestore(&read_persistent_clock_lock, flags);
> }
>
> /**
--
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