[PATCH 4/5] timers: remove memory barriers

[PATCH 4/5] timers: remove memory barriers

[Oleg Nesterov]

del_timer() and __run_timers() use smp_wmb() before
clearing timer's pending flag. It was needed because
__mod_timer() did not locked old_base if the timer is
not pending, so __mod_timer()->internal_add_timer()
can race with del_timer()->list_del().

With the previous patch these functions are serialized
through base->lock, so the barrier can be killed.

Still needed in del_timer_sync(), because it clears ->_base.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- 2.6.12-rc1/kernel/timer.c~4_BARR	2005-03-19 22:26:50.000000000 +0300
+++ 2.6.12-rc1/kernel/timer.c	2005-03-19 22:28:34.000000000 +0300
@@ -337,8 +337,6 @@ repeat:
 		goto repeat;
 	}
 	list_del(&timer->entry);
-	/* Need to make sure that anybody who sees a NULL base also sees the list ops */
-	smp_wmb();
 	__set_base(timer, base, 0);
 	spin_unlock_irqrestore(&base->lock, flags);
 
@@ -496,7 +494,6 @@ repeat:
 
 			list_del(&timer->entry);
 			set_running_timer(base, timer);
-			smp_wmb();
 			__set_base(timer, base, 0);
 			spin_unlock_irq(&base->lock);
 			{