[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20070420212057.GB820@tv-sign.ru>
Date: Sat, 21 Apr 2007 01:20:57 +0400
From: Oleg Nesterov <oleg@...sign.ru>
To: Gautham R Shenoy <ego@...ibm.com>
Cc: "Rafael J. Wysocki" <rjw@...k.pl>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, mingo@...e.hu, vatsa@...ibm.com,
paulmck@...ibm.com, pavel@....cz
Subject: Re: [RFC PATCH(experimental) 2/2] Fix freezer-kthread_stop race
On 04/20, Gautham R Shenoy wrote:
>
> On Fri, Apr 20, 2007 at 10:54:36AM +0200, Rafael J. Wysocki wrote:
> >
> > Hmm, can't we do something like this instead:
> >
> > ---
> > kernel/kthread.c | 10 ++++++++++
> > 1 file changed, 10 insertions(+)
> >
> > Index: linux-2.6.21-rc7/kernel/kthread.c
> > ===================================================================
> > --- linux-2.6.21-rc7.orig/kernel/kthread.c
> > +++ linux-2.6.21-rc7/kernel/kthread.c
> > @@ -13,6 +13,7 @@
> > #include <linux/file.h>
> > #include <linux/module.h>
> > #include <linux/mutex.h>
> > +#include <linux/freezer.h>
> > #include <asm/semaphore.h>
> >
> > /*
> > @@ -232,6 +233,15 @@ int kthread_stop(struct task_struct *k)
> >
> > /* Now set kthread_should_stop() to true, and wake it up. */
> > kthread_stop_info.k = k;
> > + if (!(current->flags & PF_NOFREEZE)) {
> > + /* If we are freezable, the freezer will wait for us */
> > + task_lock(k);
> > + k->flags |= PF_NOFREEZE;
> > + if (frozen(k))
> > + k->flags &= ~PF_FROZEN;
> > +
> > + task_unlock(k);
> > + }
>
> Yes, we can do this for now since the tasks have only two freeze states,
> namely Freezeable and Non Freezeable.
No, we can't change k->flags, k owns its ->flags, and it is not atomic.
Rafael, may I suggest you to document task_lock() in thaw_process() ? This
looks really confusing, as if task_lock() protects "p->flags &= ~PF_FROZEN".
Actually, task_lock() is needed to prevent the race with refrigerator()
when the freezing fails, but this is not obvious.
Oleg.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists