[RESEND v2] irq: Refactor irq_wait_for_interrupt info to simplify the code

[RESEND v2] irq: Refactor irq_wait_for_interrupt info to simplify the code

[chengkaitao]

From: Kaitao Cheng <pilgrimtao@gmail.com>

Cleanup extra if(test_and_clear_bit), and put the other one in front.

Signed-off-by: Kaitao Cheng <pilgrimtao@gmail.com>
---
 kernel/irq/manage.c | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 1753486b440c..7266d0d30fa9 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -863,21 +863,15 @@ static int irq_wait_for_interrupt(struct irqaction *action)
 	for (;;) {
 		set_current_state(TASK_INTERRUPTIBLE);
 
-		if (kthread_should_stop()) {
-			/* may need to run one last time */
-			if (test_and_clear_bit(IRQTF_RUNTHREAD,
-					       &action->thread_flags)) {
-				__set_current_state(TASK_RUNNING);
-				return 0;
-			}
+		if (test_and_clear_bit(IRQTF_RUNTHREAD,
+					&action->thread_flags)) {
 			__set_current_state(TASK_RUNNING);
-			return -1;
+			return 0;
 		}
 
-		if (test_and_clear_bit(IRQTF_RUNTHREAD,
-				       &action->thread_flags)) {
+		if (kthread_should_stop()) {
 			__set_current_state(TASK_RUNNING);
-			return 0;
+			return -1;
 		}
 		schedule();
 	}
-- 
2.20.1

Re: [RESEND v2] irq: Refactor irq_wait_for_interrupt info to simplify the code

[Thomas Gleixner]

chengkaitao <pilgrimtao@gmail.com> writes:
> From: Kaitao Cheng <pilgrimtao@gmail.com>
>
> Cleanup extra if(test_and_clear_bit), and put the other one in front.

That simplifies the code but opens a race window:

 CPU 0                                CPU 1
                                      irq_wait_for_interrupt()
                                        has not yet reached schedule()
 free_irq()
   remove_action();
   synchronize_irq();                   

   #ifdef CONFIG_DEBUG_SHIRQ
    action->handler()                   if (test_and_clear_bit())
                            ---> bit is not set yet                                           
      --> SET thread running
   #endif                               

   kthread_stop()                       if (kthread_stop())

                   ---> Leave with bit set and thread active count != 0

That's just the most obvious example...

Thanks,

        tglx