linux-kernel - Re: [PATCH] irq: Fix race condition when stopping the irq thread

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Message-ID: <alpine.LFD.2.02.1112012221380.2735@ionos>
Date:	Thu, 1 Dec 2011 22:23:22 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Ido Yariv <ido@...ery.com>
cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] irq: Fix race condition when stopping the irq thread

On Thu, 1 Dec 2011, Ido Yariv wrote:

> In irq_wait_for_interrupt(), the should_stop member is verified before
> setting the task's state to TASK_INTERRUPTIBLE and calling schedule().
> In case kthread_stop sets should_stop and wakes up the process after
> should_stop is checked by the irq thread but before the task's state is
> changed, the irq thread might never exit:
> 
> kthread_stop                            irq_wait_for_interrupt
> ------------                            ----------------------
> 
>                                         ...
> ...                                     while (!kthread_should_stop()) {
> kthread->should_stop = 1;
> wake_up_process(k);
> wait_for_completion(&kthread->exited);
> ...
>                                             set_current_state(TASK_INTERRUPTIBLE);
> 
>                                             ...
> 
>                                             schedule();
>                                         }
>                                         ...
> 
> Fix this by checking if the thread should stop after modifying the
> task's state.

Good catch! I restructure it to:

--- tip.orig/kernel/irq/manage.c
+++ tip/kernel/irq/manage.c
@@ -623,8 +623,9 @@ static irqreturn_t irq_nested_primary_ha
 
 static int irq_wait_for_interrupt(struct irqaction *action)
 {
+	set_current_state(TASK_INTERRUPTIBLE);
+
 	while (!kthread_should_stop()) {
-		set_current_state(TASK_INTERRUPTIBLE);
 
 		if (test_and_clear_bit(IRQTF_RUNTHREAD,
 				       &action->thread_flags)) {
@@ -632,7 +633,9 @@ static int irq_wait_for_interrupt(struct
 			return 0;
 		}
 		schedule();
+		set_current_state(TASK_INTERRUPTIBLE);
 	}
+	__set_current_state(TASK_RUNNING);
 	return -1;
 }
 
That saves us the extra conditional in the loop.

Thanks,

	tglx
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