linux-kernel - Re: [RFC][PATCH][EXPERIMENTAL] Make kernel threads nonfreezable by default

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Message-Id: <200705290051.23006.rjw@sisk.pl>
Date:	Tue, 29 May 2007 00:51:22 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	nigel@...el.suspend2.net
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Gautham R Shenoy <ego@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...sign.ru>, Pavel Machek <pavel@....cz>
Subject: Re: [RFC][PATCH][EXPERIMENTAL] Make kernel threads nonfreezable by default

On Monday, 28 May 2007 23:26, Nigel Cunningham wrote:
> Hi.
> 
> On Mon, 2007-05-28 at 20:17 +0200, Rafael J. Wysocki wrote:
> > On Monday, 28 May 2007 11:46, Nigel Cunningham wrote:
> > > Hello!
> > > 
> > > In reply to your more recent message, I had looked but not tried, so
> > > didn't feel in a position to reply yet.
> > > 
> > > On Sun, 2007-05-27 at 00:12 +0200, Rafael J. Wysocki wrote:
> > > >  63 files changed, 78 insertions(+), 138 deletions(-)
> > > 
> > > Well, that looks good, for a start :)
> > > 
> > > > Index: linux-2.6.22-rc3/kernel/exit.c
> > > > ===================================================================
> > > > --- linux-2.6.22-rc3.orig/kernel/exit.c
> > > > +++ linux-2.6.22-rc3/kernel/exit.c
> > > > @@ -389,6 +389,11 @@ void daemonize(const char *name, ...)
> > > >  	 * they would be locked into memory.
> > > >  	 */
> > > >  	exit_mm(current);
> > > > +	/*
> > > > +	 * We don't want to have TIF_FREEZE set if the system-wide hibernation
> > > > +	 * or suspend transision begins right now.
> > > > +	 */
> > > > +	current->flags |= PF_NOFREEZE;
> > > 
> > > s/transision/transition
> > 
> > Thanks, will fix.
> > 
> > > >  	set_special_pids(1, 1);
> > > >  	proc_clear_tty(current);
> > > > Index: linux-2.6.22-rc3/include/linux/freezer.h
> > > > ===================================================================
> > > > --- linux-2.6.22-rc3.orig/include/linux/freezer.h
> > > > +++ linux-2.6.22-rc3/include/linux/freezer.h
> > > > @@ -118,6 +118,14 @@ static inline int freezer_should_skip(st
> > > >  	return !!(p->flags & PF_FREEZER_SKIP);
> > > >  }
> > > >  
> > > > +/*
> > > > + * Tell the freezer that the current task should be frozen by it
> > > > + */
> > > > +static inline void set_freezable(void)
> > > > +{
> > > > +	current->flags &= ~PF_NOFREEZE;
> > > > +}
> > > > +
> > > 
> > > Given the clearing of the flag above, should we just have a
> > > set_unfreezeable here that's used above (and potentially elsewhere)...
> > > (reads more)... or more generic set_[un]freezeable(task_struct *p)
> > > routines that could also be used in copy_flags below?
> > 
> > Yes, I can introduce set_unfreezeable(), although that would be used in
> > a couple of places only.
> > 
> > I don't think it's a good idea to have set_[un]freezeable(task_struct *p),
> > since only current is allowed to set/unset its flags.
> 
> The copy_flags routine changes another process's flags - that's why I
> was suggesting this.

Yes, it does, but I'm dropping the clearing of PF_NOFREEZE from there,
not adding anything new. :-)

Greetings,
Rafael
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