[PATCH 3.16.y-ckt 114/128] genirq: Prevent chip buslock deadlock

From: Luis Henriques
Date: Sun Jan 24 2016 - 17:10:54 EST

3.16.7-ckt23 -stable review patch. If anyone has any objections, please let me know.


From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

commit abc7e40c81d113ef4bacb556f0a77ca63ac81d85 upstream.

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

interrupt(X) (Shared or spurious)
free_irq(X) interrupt_thread(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 MarkstrÃm <fredrik.markstrom@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
kernel/irq/manage.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 3dc6a61bf06a..efd80f0af47f 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -1311,6 +1311,7 @@ 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);

@@ -1324,7 +1325,7 @@ 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;

@@ -1349,6 +1350,7 @@ static struct irqaction *__free_irq(unsigned int irq, void *dev_id)

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

unregister_handler_proc(irq, action);

@@ -1422,9 +1424,7 @@ void free_irq(unsigned int irq, void *dev_id)
desc->affinity_notify = NULL;

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