ARM: OMAP: counter: add locking to read_persistent_clock

commit 9d7d6e363b06934221b81a859d509844c97380df upstream.

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@android.com>
Signed-off-by: R Sricharan <r.sricharan@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm/plat-omap/counter_32k.c b/arch/arm/plat-omap/counter_32k.c
index 5068fe5a69104c94294a12351a7117f357111612..fd433e7a25fd8906a578d3a172df509f94e67396 100644 (file)
--- a/arch/arm/plat-omap/counter_32k.c
+++ b/arch/arm/plat-omap/counter_32k.c
@@ -50,22 +50,29 @@ 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);
+
 void 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 = timer_32k_base ? __raw_readl(timer_32k_base) : 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);
 }
 
 int __init omap_init_clocksource_32k(void)