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

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Message-ID: <20120518124051.6cd03ab0@pyramind.ukuu.org.uk>
Date:	Fri, 18 May 2012 12:40:51 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Rabin Vincent <rabin@....in>
Cc:	alan@...ux.intel.com, gregkh@...uxfoundation.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Race in vt_event_wait() during suspend/resume

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.

Alan
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