Commit abc7e40c authored Dec 13, 2015 by Thomas Gleixner

genirq: Prevent chip buslock deadlock



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>
Cc: stable@vger.kernel.org

parent 9f9499ae

kernel/irq/manage.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -1434,6 +1434,7 @@ static struct irqaction __free_irq(unsigned int irq, void dev_id)
		if (!desc)
		return NULL;

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

		/*
		@@ -1447,7 +1448,7 @@ static struct irqaction __free_irq(unsigned int irq, void dev_id)
		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;
		}

		@@ -1475,6 +1476,7 @@ static struct irqaction __free_irq(unsigned int irq, void dev_id)
		#endif

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

		unregister_handler_proc(irq, action);

		@@ -1553,9 +1555,7 @@ void free_irq(unsigned int irq, void *dev_id)
		desc->affinity_notify = NULL;
		#endif

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