[125/272] genirq: Prevent irq storm on migration

[Greg KH]

2.6.37-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

commit f1a06390d013244e721372b3f9b66e39b6429c71 upstream.

move_native_irq() masks and unmasks the interrupt line
unconditionally, but the interrupt line might be masked due to a
threaded oneshot handler in progress. Unmasking the line in that case
can lead to interrupt storms. Observed on PREEMPT_RT.

Originally-from: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 kernel/irq/migration.c |   14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

--- a/kernel/irq/migration.c
+++ b/kernel/irq/migration.c
@@ -56,6 +56,7 @@ void move_masked_irq(int irq)
 void move_native_irq(int irq)
 {
 	struct irq_desc *desc = irq_to_desc(irq);
+	bool masked;
 
 	if (likely(!(desc->status & IRQ_MOVE_PENDING)))
 		return;
@@ -63,8 +64,15 @@ void move_native_irq(int irq)
 	if (unlikely(desc->status & IRQ_DISABLED))
 		return;
 
-	desc->irq_data.chip->irq_mask(&desc->irq_data);
+	/*
+	 * Be careful vs. already masked interrupts. If this is a
+	 * threaded interrupt with ONESHOT set, we can end up with an
+	 * interrupt storm.
+	 */
+	masked = desc->status & IRQ_MASKED;
+	if (!masked)
+		desc->irq_data.chip->irq_mask(&desc->irq_data);
 	move_masked_irq(irq);
-	desc->irq_data.chip->irq_unmask(&desc->irq_data);
+	if (!masked)
+		desc->irq_data.chip->irq_unmask(&desc->irq_data);
 }
-


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