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Subject[125/272] genirq: Prevent irq storm on migration
2.6.37-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Thomas Gleixner <tglx@linutronix.de>

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@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
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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