linux-kernel - Re: Race in vt_event_wait() during suspend/resume

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Date:	Fri, 18 May 2012 11:06:28 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Rabin Vincent <rabin@....in>, alan@...ux.intel.com,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Race in vt_event_wait() during suspend/resume

On Fri, May 18, 2012 at 12:40:51PM +0100, Alan Cox wrote:
> On Fri, 18 May 2012 16:34:53 +0530
> Rabin Vincent <rabin@....in> wrote:
> 
> > pm_restore_console() is called from the suspend/resume path,
> > this calls vt_move_to_console(), which calls vt_event_wait().
> > 
> > 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
> > 
> > I think the following should fix it.  Comments?
> > 
> 
> Looks right to me.

Great, Rabin, care to resend it with a proper Signed-off-by: line so
that I can apply it?

thanks,

greg k-h
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