Re: [RFC][PATCH -mm 3/3] freezer: Fix problem with kthread_stop

Pavel Machek
2007-04-23T10:40:37Z

Hi!

> Fix the problem with kthread_stop() that causes the freezer to fail if a
> freezable thread is attempting to stop a frozen one and that may cause the
> freezer to fail if the thread being stopped is freezable and
> try_to_freeze_tasks() is running concurrently with kthread_stop().

Parse error.

> Index: linux-2.6.21-rc6-mm1/kernel/kthread.c
> ===================================================================
> --- linux-2.6.21-rc6-mm1.orig/kernel/kthread.c 2007-04-09 15:23:48.000000000 +0200
> +++ linux-2.6.21-rc6-mm1/kernel/kthread.c 2007-04-22 19:05:29.000000000 +0200
> @@ -232,6 +233,14 @@ int kthread_stop(struct task_struct *k)
>
> /* Now set kthread_should_stop() to true, and wake it up. */
> kthread_stop_info.k = k;
> + if (!freezer_should_exempt(current)) {
> + /* We are freezable, so we must make sure that the thread being
> + * stopped is not frozen and will not be frozen until it dies
> + */
> + freezer_exempt(k);
> + if (frozen(k))
> + clear_frozen_flag(k);
> + }
> wake_up_process(k);
> put_task_struct(k);
>

Do we need to take some locks to access other process' flags? Or do
frozen_exempt() etc take enough locks, already?
Pavel
--
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