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Subject[PATCH 3.2 40/70] genirq: Prevent chip buslock deadlock
3.2.76-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Thomas Gleixner <tglx@linutronix.de>

commit abc7e40c81d113ef4bacb556f0a77ca63ac81d85 upstream.

If a interrupt chip utilizes chip->buslock then free_irq() can
deadlock in the following way:

CPU0 CPU1
interrupt(X) (Shared or spurious)
free_irq(X) interrupt_thread(X)
chip_bus_lock(X)
irq_finalize_oneshot(X)
chip_bus_lock(X)
synchronize_irq(X)

synchronize_irq() waits for the interrupt thread to complete,
i.e. forever.

Solution is simple: Drop chip_bus_lock() before calling
synchronize_irq() as we do with the irq_desc lock. There is nothing to
be protected after the point where irq_desc lock has been released.

This adds chip_bus_lock/unlock() to the remove_irq() code path, but
that's actually correct in the case where remove_irq() is called on
such an interrupt. The current users of remove_irq() are not affected
as none of those interrupts is on a chip which requires buslock.

Reported-by: Fredrik Markström <fredrik.markstrom@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
kernel/irq/manage.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -1200,6 +1200,7 @@ static struct irqaction *__free_irq(unsi
if (!desc)
return NULL;

+ chip_bus_lock(desc);
raw_spin_lock_irqsave(&desc->lock, flags);

/*
@@ -1213,7 +1214,7 @@ static struct irqaction *__free_irq(unsi
if (!action) {
WARN(1, "Trying to free already-free IRQ %d\n", irq);
raw_spin_unlock_irqrestore(&desc->lock, flags);
-
+ chip_bus_sync_unlock(desc);
return NULL;
}

@@ -1242,6 +1243,7 @@ static struct irqaction *__free_irq(unsi
#endif

raw_spin_unlock_irqrestore(&desc->lock, flags);
+ chip_bus_sync_unlock(desc);

unregister_handler_proc(irq, action);

@@ -1316,9 +1318,7 @@ void free_irq(unsigned int irq, void *de
desc->affinity_notify = NULL;
#endif

- chip_bus_lock(desc);
kfree(__free_irq(irq, dev_id));
- chip_bus_sync_unlock(desc);
}
EXPORT_SYMBOL(free_irq);


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