linux-kernel - Re: [RFC][PATCH 3/3] Freezer: Prevent ___call_usermodehelper from missing freezing requests

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Message-Id: <200702261930.56550.rjw@sisk.pl>
Date:	Mon, 26 Feb 2007 19:30:55 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Aneesh Kumar" <aneesh.kumar@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"Andrew Morton" <akpm@...l.org>, "Oleg Nesterov" <oleg@...sign.ru>,
	"Pavel Machek" <pavel@....cz>,
	"Srivatsa Vaddagiri" <vatsa@...ibm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"Gautham R Shenoy" <ego@...ibm.com>
Subject: Re: [RFC][PATCH 3/3] Freezer: Prevent ___call_usermodehelper from missing freezing requests

On Monday, 26 February 2007 12:58, Aneesh Kumar wrote:
> On 2/26/07, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > NOTE: Alternatively, we can just drop flush_signals() from there, but I'm not
> > sure that's the right thing to do.
> >
> > ---
> > From: Rafael J. Wysocki <rjw@...k.pl>
> >
> > Since ____call_usermodehelper() calls flush_signals(current), the task that
> > enters it may miss a freezing request.  However, if ____call_usermodehelper()
> > clears TIF_FREEZE for the current task after flush_signals(current) returns, the
> > freezer will generate one more freezing request for this task.
> >
> > Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> > ---
> >  kernel/kmod.c |    2 ++
> >  1 file changed, 2 insertions(+)
> >
> > Index: linux-2.6.20-mm2/kernel/kmod.c
> > ===================================================================
> > --- linux-2.6.20-mm2.orig/kernel/kmod.c 2007-02-25 12:07:15.000000000 +0100
> > +++ linux-2.6.20-mm2/kernel/kmod.c      2007-02-25 12:49:16.000000000 +0100
> > @@ -34,6 +34,7 @@
> >  #include <linux/kernel.h>
> >  #include <linux/init.h>
> >  #include <linux/resource.h>
> > +#include <linux/freezer.h>
> >  #include <asm/uaccess.h>
> >
> >  extern int delete_module(const char *name, unsigned int flags);
> > @@ -258,6 +259,7 @@ static int ____call_usermodehelper(void
> >         new_session = key_get(sub_info->ring);
> >         flush_signals(current);
> >         spin_lock_irq(&current->sighand->siglock);
> > +       do_not_freeze(current);
> >         old_session = __install_session_keyring(current, new_session);
> >         flush_signal_handlers(current, 1);
> >         sigemptyset(&current->blocked);
> >
> 
> 
> this need a comment . Otherwise one reading will read it as we don't
> want it to freeze.
> 
> How about
> /*
> clears TIF_FREEZE for the current task after flush_signals(current)
> returns, so that the
> freezer will generate one more freezing request for this task.
> 
> */

Looks reasonable, but Oleg wants to drop the flush_signals(current) ...

Rafael
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