linux-kernel - Re: [PATCH] vt: fix race in vt

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Date:	Thu, 14 Jun 2012 10:48:02 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Alan Cox <alan@...ux.intel.com>,
	Rabin Vincent <rabin.vincent@...ricsson.com>,
	linux-kernel@...r.kernel.org, rabin@....in
Subject: Re: [PATCH] vt: fix race in vt_waitactive()

On Wed, 13 Jun 2012 16:44:52 -0700
Greg KH <gregkh@...uxfoundation.org> wrote:

> On Mon, May 21, 2012 at 01:38:42PM +0530, Rabin Vincent wrote:
> > pm_restore_console() is called from the suspend/resume path, and this
> > calls vt_move_to_console(), which calls vt_waitactive().
> > 
> > There's a race in this path which causes the process which requests the
> > suspend to sleep indefinitely waiting for an event which already
> > happened:
> > 
> > P1                                      P2
> >  vt_move_to_console()
> >   set_console()
> >     schedule_console_callback()
> >   vt_waitactive()
> >     check n == fg_console +1
> >                                        console_callback()
> >                                          switch_screen()
> >                                          vt_event_post() // no waiters
> > 
> >     vt_event_wait() // forever
> > 
> > Fix the race by ensuring we're registered for the event before we check
> > if it's already completed.
> > 
> > Cc: Alan Cox <alan@...ux.intel.com>
> > Signed-off-by: Rabin Vincent <rabin.vincent@...ricsson.com>
> > ---
> >  drivers/tty/vt/vt_ioctl.c |   47 ++++++++++++++++++++++++++++++++------------
> >  1 files changed, 34 insertions(+), 13 deletions(-)
> 
> Alan, any thoughts on this patch?

I acked it when first posted - I believe its correct.
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