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SubjectRe: [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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