powerpc/tm: Remove interrupt disable in __switch_to()

We currently turn IRQs off in __switch_to(0 but this is unnecessary as it's
already disabled in the caller.

This removes the IRQ disable but adds a check to make sure it is really off
in case this changes in future.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/process.c

@@ -597,12 +597,13 @@ struct task_struct *__switch_to(struct task_struct *prev,
 	struct task_struct *new)
 {
 	struct thread_struct *new_thread, *old_thread;
-	unsigned long flags;
 	struct task_struct *last;
 #ifdef CONFIG_PPC_BOOK3S_64
 	struct ppc64_tlb_batch *batch;
 #endif
 
+	WARN_ON(!irqs_disabled());
+
 	/* Back up the TAR across context switches.
 	 * Note that the TAR is not available for use in the kernel.  (To
 	 * provide this, the TAR should be backed up/restored on exception
@@ -722,8 +723,6 @@ struct task_struct *__switch_to(struct task_struct *prev,
 	}
 #endif /* CONFIG_PPC_BOOK3S_64 */
 
-	local_irq_save(flags);
-
 	/*
 	 * We can't take a PMU exception inside _switch() since there is a
 	 * window where the kernel stack SLB and the kernel stack are out
@@ -743,8 +742,6 @@ struct task_struct *__switch_to(struct task_struct *prev,
 	}
 #endif /* CONFIG_PPC_BOOK3S_64 */
 
-	local_irq_restore(flags);
-
 	return last;
 }