genirq: Get rid of unnecessary irqaction field in task_struct

When a new thread handler is created, an irqaction is passed to it as
data. Not only that irqaction is stored in task_struct by the handler
for later use, but also a structure associated with the kernel thread
keeps this value as long as the thread exists.

This fix kicks irqaction out off task_struct. Yes, I introduce new bit
field. But it allows not only to eliminate the duplicate, but also
shortens size of task_struct.

Reported-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Link: http://lkml.kernel.org/r/20120309135925.GB2114@dhcp-26-207.brq.redhat.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

include/linux/sched.h

@@ -1319,6 +1319,11 @@ struct task_struct {
 	unsigned sched_reset_on_fork:1;
 	unsigned sched_contributes_to_load:1;
 
+#ifdef CONFIG_GENERIC_HARDIRQS
+	/* IRQ handler threads */
+	unsigned irq_thread:1;
+#endif
+
 	pid_t pid;
 	pid_t tgid;
 
@@ -1427,11 +1432,6 @@ struct task_struct {
  * mempolicy */
 	spinlock_t alloc_lock;
 
-#ifdef CONFIG_GENERIC_HARDIRQS
-	/* IRQ handler threads */
-	struct irqaction *irqaction;
-#endif
-
 	/* Protection of the PI data structures: */
 	raw_spinlock_t pi_lock;