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

Alan Cox
2012-06-14T09:44:31Z

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.