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From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Andrew Morton <akpm@osdl.org>
Subject: Re: [PATCH -mm] swsusp: Freeze filesystems during suspend (rev. 2)
Date: Thu, 2 Nov 2006 21:53:56 +0100
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Cc: Pavel Machek <pavel@ucw.cz>, LKML <linux-kernel@vger.kernel.org>,
       Nigel Cunningham <ncunningham@linuxmail.org>,
       Christoph Hellwig <hch@infradead.org>
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On Wednesday, 1 November 2006 22:21, Andrew Morton wrote:
> On Wed, 1 Nov 2006 21:27:17 +0100
> "Rafael J. Wysocki" <rjw@sisk.pl> wrote:
> 
> > On Wednesday, 1 November 2006 20:45, Andrew Morton wrote:
> > > On Wed, 1 Nov 2006 18:53:07 +0100
> > > "Rafael J. Wysocki" <rjw@sisk.pl> wrote:
> > > 
> > > > +void thaw_processes(void)
> > > > +{
> > > > +	printk("Restarting tasks ... ");
> > > > +	__thaw_tasks(FREEZER_KERNEL_THREADS);
> > > > +	thaw_filesystems();
> > > > +	__thaw_tasks(FREEZER_USER_SPACE);
> > > > +	schedule();
> > > > +	printk("done.\n");
> > > > +}
> > > >  
> > > > -	read_unlock(&tasklist_lock);
> > > > +void thaw_kernel_threads(void)
> > > > +{
> > > > +	printk("Restarting kernel threads ... ");
> > > > +	__thaw_tasks(FREEZER_KERNEL_THREADS);
> > > >  	schedule();
> > > >  	printk("done.\n");
> > > >  }
> > > 
> > > what do these random-looking schedule()s do??
> > 
> > My understanding is that they allow the thawed tasks to actually exit
> > the refrigerator, because __thaw_tasks() only changes their states.
> 
> I'd be surprised if this is doing what we thing it's doing.  Calling
> schedule() in state TASK_RUNNING is usually a no-op.  It'll only actually
> switch to another task if the scheduler decides that this task has expired
> its timeslice, or another higher-priority task has become runnable, etc.

This actually can happen, it seems, because __thaw_tasks() calls
wake_up_process() for each frozen task which may call resched_task() for
current.