powerpc/64: warn if local irqs are enabled in NMI or hardirq context

This can help catch bugs such as the one fixed by the previous change
to prevent _exception() from enabling irqs.

ppc32 could have a similar warning but it has no good config option to
debug this stuff (the test may be overkill to add for production
kernels).

Signed-off-by: Nicholas Piggin <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/powerpc/kernel/irq.c

···
 		return;
 	}
 
+	if (IS_ENABLED(CONFIG_PPC_IRQ_SOFT_MASK_DEBUG))
+		WARN_ON_ONCE(in_nmi() || in_hardirq());
+
 	/*
 	 * After the stb, interrupts are unmasked and there are no interrupts
 	 * pending replay. The restart sequence makes this atomic with
···
 	irq_soft_mask_set(mask);
 	if (mask)
 		return;
+
+	if (IS_ENABLED(CONFIG_PPC_IRQ_SOFT_MASK_DEBUG))
+		WARN_ON_ONCE(in_nmi() || in_hardirq());
 
 	/*
 	 * From this point onward, we can take interrupts, preempt,