Patch "genirq: Prevent chip buslock deadlock" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

genirq: Prevent chip buslock deadlock

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
genirq-prevent-chip-buslock-deadlock.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Thomas Gleixner <[email protected]>
Date: Sun, 13 Dec 2015 18:12:30 +0100
Subject: genirq: Prevent chip buslock deadlock
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From: Thomas Gleixner <[email protected]>

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.

---
 kernel/irq/manage.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

@@ -1230,6 +1230,7 @@ static struct irqaction *__free_irq(unsi
 	if (!desc)
 		return NULL;
 
+	chip_bus_lock(desc);
 	raw_spin_lock_irqsave(&desc->lock, flags);
 
 	/*

@@ -1243,7 +1244,7 @@ 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;
 		}
 

@@ -1266,6 +1267,7 @@ static struct irqaction *__free_irq(unsi
 #endif
 
 	raw_spin_unlock_irqrestore(&desc->lock, flags);
+	chip_bus_sync_unlock(desc);
 
 	unregister_handler_proc(irq, action);
 

@@ -1339,9 +1341,7 @@ 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);
 

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/genirq-prevent-chip-buslock-deadlock.patch queue-3.14/sched-rt-remove-return-value-from-pull_rt_task.patch queue-3.14/sched-replace-post_schedule-with-a-balance-callback-list.patch queue-3.14/sched-dl-convert-switched_-from-to-_dl-prio_changed_dl-to-balance-callbacks.patch queue-3.14/sched-dl-remove-return-value-from-pull_dl_task.patch queue-3.14/sched-allow-balance-callbacks-for-check_class_changed.patch queue-3.14/sched-rt-convert-switched_-from-to-_rt-prio_changed_rt-to-balance-callbacks.patch