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>

2 files changed, 16 insertions, 13 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 7d379a6bfd88..07f537a371ce 100644
--- a/include/linux/sched.h
+++ b/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;
 
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index c0730ad8a117..0fa3ce998ecb 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -780,7 +780,7 @@ static int irq_thread(void *data)
                 handler_fn = irq_thread_fn;
 
         sched_setscheduler(current, SCHED_FIFO, &param);
-        current->irqaction = action;
+        current->irq_thread = 1;
 
         while (!irq_wait_for_interrupt(action)) {
 
@@ -818,10 +818,10 @@ static int irq_thread(void *data)
         irq_finalize_oneshot(desc, action, true);
 
         /*
-         * Clear irqaction. Otherwise exit_irq_thread() would make
+         * Clear irq_thread. Otherwise exit_irq_thread() would make
          * fuzz about an active irq thread going into nirvana.
          */
-        current->irqaction = NULL;
+        current->irq_thread = 0;
         return 0;
 }
 
@@ -832,27 +832,30 @@ void exit_irq_thread(void)
 {
         struct task_struct *tsk = current;
         struct irq_desc *desc;
+        struct irqaction *action;
 
-        if (!tsk->irqaction)
+        if (!tsk->irq_thread)
                 return;
 
+        action = kthread_data(tsk);
+
         printk(KERN_ERR
                "exiting task \"%s\" (%d) is an active IRQ thread (irq %d)\n",
-               tsk->comm ? tsk->comm : "", tsk->pid, tsk->irqaction->irq);
+               tsk->comm ? tsk->comm : "", tsk->pid, action->irq);
 
-        desc = irq_to_desc(tsk->irqaction->irq);
+        desc = irq_to_desc(action->irq);
 
         /*
          * Prevent a stale desc->threads_oneshot. Must be called
          * before setting the IRQTF_DIED flag.
          */
-        irq_finalize_oneshot(desc, tsk->irqaction, true);
+        irq_finalize_oneshot(desc, action, true);
 
         /*
          * Set the THREAD DIED flag to prevent further wakeups of the
          * soon to be gone threaded handler.
          */
-        set_bit(IRQTF_DIED, &tsk->irqaction->flags);
+        set_bit(IRQTF_DIED, &action->flags);
 }
 
 static void irq_setup_forced_threading(struct irqaction *new)