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

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Date:	Thu, 14 Jun 2012 10:20:45 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
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 Thu, Jun 14, 2012 at 10:48:02AM +0100, Alan Cox wrote:
> 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.

Ah, sorry, I missed that somehow.  I'll go queue it up now.

greg k-h
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