powerpc/irq: Don't WARN continuously in arch_local_irq_restore()

When CONFIG_PPC_IRQ_SOFT_MASK_DEBUG is enabled (uncommon), we have a
series of WARN_ON's in arch_local_irq_restore().

These are "should never happen" conditions, but if they do happen they
can flood the console and render the system unusable. So switch them
to WARN_ON_ONCE().

Fixes: e2b36d59 ("powerpc/64: Don't trace code that runs with the soft irq mask unreconciled")
Fixes: 9b81c021 ("powerpc/64s: make PACA_IRQ_HARD_DIS track MSR[EE] closely")
Fixes: 7c0482e3 ("powerpc/irq: Fix another case of lazy IRQ state getting out of sync")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190708061046.7075-1-mpe@ellerman.id.au

arch/powerpc/kernel/irq.c

@@ -259,7 +259,7 @@ notrace void arch_local_irq_restore(unsigned long mask)
 	irq_happened = get_irq_happened();
 	if (!irq_happened) {
 #ifdef CONFIG_PPC_IRQ_SOFT_MASK_DEBUG
-		WARN_ON(!(mfmsr() & MSR_EE));
+		WARN_ON_ONCE(!(mfmsr() & MSR_EE));
 #endif
 		return;
 	}
@@ -272,7 +272,7 @@ notrace void arch_local_irq_restore(unsigned long mask)
 	 */
 	if (!(irq_happened & PACA_IRQ_HARD_DIS)) {
 #ifdef CONFIG_PPC_IRQ_SOFT_MASK_DEBUG
-		WARN_ON(!(mfmsr() & MSR_EE));
+		WARN_ON_ONCE(!(mfmsr() & MSR_EE));
 #endif
 		__hard_irq_disable();
 #ifdef CONFIG_PPC_IRQ_SOFT_MASK_DEBUG
@@ -283,7 +283,7 @@ notrace void arch_local_irq_restore(unsigned long mask)
 		 * warn if we are wrong. Only do that when IRQ tracing
 		 * is enabled as mfmsr() can be costly.
 		 */
-		if (WARN_ON(mfmsr() & MSR_EE))
+		if (WARN_ON_ONCE(mfmsr() & MSR_EE))
 			__hard_irq_disable();
 #endif
 	}