linux-kernel - [PATCH 3.2 40/70] genirq: Prevent chip buslock deadlock

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Message-ID: <lsq.1453087115.858367442@decadent.org.uk>
Date:	Mon, 18 Jan 2016 03:18:35 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Thomas Gleixner" <tglx@...utronix.de>,
	"Fredrik Markström" <fredrik.markstrom@...il.com>
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@...utronix.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@...il.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Ben Hutchings <ben@...adent.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);