2012-02-20 17:31:27

by Alexander Gordeev

Subject: [PATCH 2/5] 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 <[email protected]>
Signed-off-by: Alexander Gordeev <[email protected]>
---
include/linux/sched.h | 10 +++++-----
kernel/irq/manage.c | 19 +++++++++++--------
2 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 7d379a6..07f537a 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 c0730ad..0fa3ce9 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)
--
1.7.7.6