Patch "genirq: Prevent chip buslock deadlock" has been added to the 3.10-stable tree

[<gregkh@linuxfoundation.org>]

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

    genirq: Prevent chip buslock deadlock

to the 3.10-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-3.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From abc7e40c81d113ef4bacb556f0a77ca63ac81d85 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Sun, 13 Dec 2015 18:12:30 +0100
Subject: genirq: Prevent chip buslock deadlock
MIME-Version: 1.0
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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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -1229,6 +1229,7 @@ static struct irqaction *__free_irq(unsi
 	if (!desc)
 		return NULL;
 
+	chip_bus_lock(desc);
 	raw_spin_lock_irqsave(&desc->lock, flags);
 
 	/*
@@ -1242,7 +1243,7 @@ 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;
 		}
 
@@ -1265,6 +1266,7 @@ static struct irqaction *__free_irq(unsi
 #endif
 
 	raw_spin_unlock_irqrestore(&desc->lock, flags);
+	chip_bus_sync_unlock(desc);
 
 	unregister_handler_proc(irq, action);
 
@@ -1338,9 +1340,7 @@ 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 tglx@linutronix.de are

queue-3.10/genirq-prevent-chip-buslock-deadlock.patch