[PATCH 28/40] ARM: sched_clock: provide common infrastructure for sched_clock()

[Russell King - ARM Linux]

On Fri, Dec 17, 2010 at 07:05:54PM +0000, Russell King - ARM Linux wrote:
> Yes, you're right, it should disable local IRQs across the update.  Thanks
> for spotting.

Here's the incremental patch for it.  Note that we can safely explicitly
disable and re-enable IRQs as the timer subsystem ensures that we will
always be called with IRQs enabled:

                        spin_unlock_irq(&base->lock);
                        call_timer_fn(timer, fn, data);
                        spin_lock_irq(&base->lock);

diff --git a/arch/arm/include/asm/sched_clock.h b/arch/arm/include/asm/sched_clock.h
index 82d4d3f..5643cb0 100644
--- a/arch/arm/include/asm/sched_clock.h
+++ b/arch/arm/include/asm/sched_clock.h
@@ -30,7 +30,7 @@ static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
  * Atomically update the sched_clock epoch.  Your update callback will
  * be called from a timer before the counter wraps - read the current
  * counter value, and call this function to safely move the epochs
- * forward.
+ * forward.  Only use this from the update callback.
  */
 static inline void update_sched_clock(struct clock_data *cd, u32 cyc, u32 mask)
 {
@@ -41,11 +41,13 @@ static inline void update_sched_clock(struct clock_data *cd, u32 cyc, u32 mask)
 	 * Write epoch_cyc and epoch_ns in a way that the update is
 	 * detectable in cyc_to_fixed_sched_clock().
 	 */
+	local_irq_disable();
 	cd->epoch_cyc = cyc;
 	smp_wmb();
 	cd->epoch_ns = ns;
 	smp_wmb();
 	cd->epoch_cyc_copy = cyc;
+	local_irq_enable();
 }
 
 /*