[RFC patch 1/4] genirq: Globally serialize request/free_irq

[Thomas Gleixner]

request/free_irq is not a hotpath, so we can afford to serialize it
with a global lock. That allows us to shorten critical sections as the
action chain of an irq descriptor becomes protected by the global
lock. It's also a prerequisite for further changes which provide
adaptive oneshot functionality for possibly shared interrupts.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Tom Lyon <pugs@xxxxxxxxx>
Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
Cc: Avi Kivity <avi@xxxxxxxxxx>
Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Cc: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
Cc: Jan Kiszka <jan.kiszka@xxxxxx>
---
 kernel/irq/manage.c |   19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

Index: linux-2.6-tip/kernel/irq/manage.c
===================================================================
--- linux-2.6-tip.orig/kernel/irq/manage.c
+++ linux-2.6-tip/kernel/irq/manage.c
@@ -14,9 +14,12 @@
 #include <linux/interrupt.h>
 #include <linux/slab.h>
 #include <linux/sched.h>
+#include <linux/mutex.h>
 
 #include "internals.h"
 
+static DEFINE_MUTEX(register_lock);
+
 /**
  *	synchronize_irq - wait for pending IRQ handlers (on other CPUs)
  *	@irq: interrupt number to wait for
@@ -870,8 +873,12 @@ out_thread:
 int setup_irq(unsigned int irq, struct irqaction *act)
 {
 	struct irq_desc *desc = irq_to_desc(irq);
+	int ret;
 
-	return __setup_irq(irq, desc, act);
+	mutex_lock(&register_lock);
+	ret = __setup_irq(irq, desc, act);
+	mutex_unlock(&register_lock);
+	return ret;
 }
 EXPORT_SYMBOL_GPL(setup_irq);
 
@@ -977,7 +984,9 @@ static struct irqaction *__free_irq(unsi
  */
 void remove_irq(unsigned int irq, struct irqaction *act)
 {
+	mutex_lock(&register_lock);
 	__free_irq(irq, act->dev_id);
+	mutex_unlock(&register_lock);
 }
 EXPORT_SYMBOL_GPL(remove_irq);
 
@@ -1002,9 +1011,13 @@ void free_irq(unsigned int irq, void *de
 	if (!desc)
 		return;
 
+	mutex_lock(&register_lock);
+
 	chip_bus_lock(desc);
 	kfree(__free_irq(irq, dev_id));
 	chip_bus_sync_unlock(desc);
+
+	mutex_unlock(&register_lock);
 }
 EXPORT_SYMBOL(free_irq);
 
@@ -1091,10 +1104,14 @@ int request_threaded_irq(unsigned int ir
 	action->name = devname;
 	action->dev_id = dev_id;
 
+	mutex_lock(&register_lock);
+
 	chip_bus_lock(desc);
 	retval = __setup_irq(irq, desc, action);
 	chip_bus_sync_unlock(desc);
 
+	mutex_unlock(&register_lock);
+
 	if (retval)
 		kfree(action);
 


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