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Date: Fri, 2 Mar 2007 16:58:43 -0800
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>, Anton Blanchard <anton@samba.org>,
       Andrew Morton <akpm@osdl.org>, Pavel Machek <pavel@ucw.cz>,
       LKML <linux-kernel@vger.kernel.org>,
       Aneesh Kumar <aneesh.kumar@gmail.com>,
       Srivatsa Vaddagiri <vatsa@in.ibm.com>,
       Gautham R Shenoy <ego@in.ibm.com>
Subject: Re: [PATCH -mm 3/7] Freezer: Remove PF_NOFREEZE from rcutorture thread
Message-ID: <20070303005843.GG2373@linux.vnet.ibm.com>
Reply-To: paulmck@linux.vnet.ibm.com
References: <200702260800.49603.rjw@sisk.pl> <200703011609.43804.rjw@sisk.pl> <20070301193826.GA14587@kryten> <200703012054.26940.rjw@sisk.pl> <20070302213549.GC2373@linux.vnet.ibm.com> <20070302233337.GA267@tv-sign.ru>
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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.

Is this what you had in mind?

							Thanx, Paul