cpuidle: always return with interrupts enabled

In the case where cpuidle_idle_call() returns before changing state due to
a need_resched(), it was returning with IRQs disabled.

The idle path assumes that the platform specific idle code returns with
interrupts enabled (although this too is undocumented AFAICT) and on ARM
we have a WARN_ON(!(irqs_disabled()) when returning from the idle loop, so
the user-visible effects were only a warning since interrupts were
eventually re-enabled later.

On x86, this same problem exists, but there is no WARN_ON() to detect it.
As on ARM, the interrupts are eventually re-enabled, so I'm not sure of
any actual bugs triggered by this. It's primarily a
correctness/consistency fix.

This patch ensures IRQs are (re)enabled before returning.

Reported-by: Hemanth V <[e-mail]>
Signed-off-by: Kevin Hilman <[e-mail]>
Cc: Arjan van de Ven <[e-mail]>
Cc: Len Brown <[e-mail]>
Cc: Venkatesh Pallipadi <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: "Rafael J. Wysocki" <[e-mail]>
Tested-by: Martin Michlmayr <[e-mail]>
Cc: <[e-mail]> [2.6.31.x]
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/cpuidle/cpuidle.c

···
 #endif
 	/* ask the governor for the next state */
 	next_state = cpuidle_curr_governor->select(dev);
-	if (need_resched())
+	if (need_resched()) {
+		local_irq_enable();
 		return;
+	}
+
 	target_state = &dev->states[next_state];
 
 	/* enter the state and update stats */