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Date: Sat, 3 Mar 2007 20:32:40 +0300
From: Oleg Nesterov <oleg@...sign.ru>
To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: "Rafael J. Wysocki" <rjw@...k.pl>,
Anton Blanchard <anton@...ba.org>,
Andrew Morton <akpm@...l.org>, Pavel Machek <pavel@....cz>,
LKML <linux-kernel@...r.kernel.org>,
Aneesh Kumar <aneesh.kumar@...il.com>,
Srivatsa Vaddagiri <vatsa@...ibm.com>,
Gautham R Shenoy <ego@...ibm.com>
Subject: Re: [PATCH -mm 3/7] Freezer: Remove PF_NOFREEZE from rcutorture thread
On 03/02, Paul E. McKenney wrote:
>
> On Sat, Mar 03, 2007 at 02:33:37AM +0300, Oleg Nesterov wrote:
> > On 03/02, Paul E. McKenney wrote:
> > >
> > > One way to embed try_to_freeze() into kthread_should_stop() might be
> > > as follows:
> > >
> > > int kthread_should_stop(void)
> > > {
> > > if (kthread_stop_info.k == current)
> > > return 1;
> > > try_to_freeze();
> > > return 0;
> > > }
> >
> > I think this is dangerous. For example, worker_thread() will probably
> > need some special actions after return from refrigerator. Also, a kernel
> > thread may check kthread_should_stop() in the place where try_to_freeze()
> > is not safe.
> >
> > Perhaps we should introduce a new helper which does this.
>
> Good point -- the return value from try_to_freeze() is lost if one uses
> the above approach. About one third of the calls to try_to_freeze()
> in 2.6.20 pay attention to the return value.
>
> One approach would be to have a kthread_should_stop_nofreeze() for those
> cases, and let the default be to try to freeze.
I personally think we should do the opposite, add kthread_should_stop_check_freeze()
or something. kthread_should_stop() is like signal_pending(), we can use
it under spin_lock (and it is probably used this way by some out-of-tree
driver). The new helper is obviously "might_sleep()".
Oleg.
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