Re: [PATCH] vt: fix race in vt_waitactive()

Greg KH
2012-06-14T17:20:56Z

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@linuxfoundation.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@linux.intel.com>
> > > Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.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