[PATCH] genirq: Fix race condition in ONESHOT irq handler

From: Lothar WaÃmann
Date: Tue Feb 07 2012 - 08:38:43 EST

There is a race condition in the threaded IRQ handler code for oneshot
interrupts that may lead to disabling an IRQ indefinitely. IRQs are
masked before calling the hard-irq handler and are unmasked only after
the soft-irq handler has been run. Thus if the hard-irq handler
returns IRQ_HANDLED instead of IRQ_WAKE_THREAD, meaning the soft-irq
will not be called, the interrupt will remain masked forever.

This can happen due to a short pulse on the interrupt line, that
triggers the interrupt logic, but goes undetected by the hard-irq
handler. The problem can be reproduced with the TSC2007 touch
controller driver that uses ONESHOT interrupts.

The problem arises also with interrupt controllers that latch a level
triggered IRQ until it is acknowledged (like the i.MX28 does).
In this case the IRQ status bit will remain asserted after the
soft-irq finishes and retrigger the interrupt while the interrupt line
is already deasserted.

Signed-off-by: Lothar WaÃmann <LW@xxxxxxxxxxxxxxxxxxx>
kernel/irq/chip.c | 9 +++++++--
1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index f7c543a..74fdef9 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -343,6 +343,8 @@ EXPORT_SYMBOL_GPL(handle_simple_irq);
handle_level_irq(unsigned int irq, struct irq_desc *desc)
+ irqreturn_t ret;

@@ -360,10 +362,13 @@ handle_level_irq(unsigned int irq, struct irq_desc *desc)
if (unlikely(!desc->action || irqd_irq_disabled(&desc->irq_data)))
goto out_unlock;

- handle_irq_event(desc);
+ ret = handle_irq_event(desc);

- if (!irqd_irq_disabled(&desc->irq_data) && !(desc->istate & IRQS_ONESHOT))
+ if (!irqd_irq_disabled(&desc->irq_data) &&
+ (!(desc->istate & IRQS_ONESHOT) ||
+ !(ret & IRQ_WAKE_THREAD)))

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