[PATCH - RESEND] IRQ: don't suspend nested_thread irqs over system suspend.

[NeilBrown]

Nested IRQs can only fire when the parent irq fires.
So when the parent is suspended, there is no need to suspend
the child irq.

Suspending nested irqs can cause a problem is they are suspended or
resumed in the wrong order.
If an interrupt fires while the parent is active but the child is
suspended, then the interrupt will not be acknowledged properly
and so an interrupt storm can result.
This is particularly likely if the parent is resumed before
the child, and the interrupt was raised during suspend.

Ensuring correct ordering would be possible, but it is simpler
to just never suspend nested interrupts.

Signed-off-by: NeilBrown <neil@xxxxxxxxxx>

---
This is a resend of a patch sent at the end of January 2015.
Rafael seemed happy with it, but I receive no other response so I'm resending.

Thanks,
NeilBrown


diff --git a/kernel/irq/pm.c b/kernel/irq/pm.c
index 3ca532592704..40cbcfb7fc43 100644
--- a/kernel/irq/pm.c
+++ b/kernel/irq/pm.c
@@ -118,6 +118,8 @@ void suspend_device_irqs(void)
 		unsigned long flags;
 		bool sync;
 
+		if (irq_settings_is_nested_thread(desc))
+			continue;
 		raw_spin_lock_irqsave(&desc->lock, flags);
 		sync = suspend_device_irq(desc, irq);
 		raw_spin_unlock_irqrestore(&desc->lock, flags);
@@ -158,6 +160,8 @@ static void resume_irqs(bool want_early)
 
 		if (!is_early && want_early)
 			continue;
+		if (irq_settings_is_nested_thread(desc))
+			continue;
 
 		raw_spin_lock_irqsave(&desc->lock, flags);
 		resume_irq(desc, irq);

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