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

Rafael J. Wysocki
2007-04-23T20:03:08Z

Hi,

On Monday, 23 April 2007 12:40, Pavel Machek wrote:
> 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.

OK, will fix.

> > 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?

After the previous patch we only use set_bit(), clear_bit() and test_bit() to
access freezer_falgs, so no special locking is needed to protect them.

Greetings,
Rafael