linux-kernel - Re: deadlock in vt_kbd_con

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Date:	Tue, 1 May 2012 14:22:52 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Clemens Ladisch <clemens@...isch.de>
Cc:	Alan Cox <alan@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: deadlock in vt_kbd_con_stop

On Tue, 1 May 2012, Clemens Ladisch wrote:

> Pressing the Scroll Lock key in the console stops scrolling rather permanently.
> (Ctrl+S/Q works fine.)
> 
> =============================================
> [ INFO: possible recursive locking detected ]
> 3.4.0-rc5+ #354 Not tainted
> ---------------------------------------------
> swapper/5/0 is trying to acquire lock:
>  (kbd_event_lock){-.....}, at: [<ffffffff8127802c>] vt_kbd_con_stop+0x1a/0x57
> 
> but task is already holding lock:
>  (kbd_event_lock){-.....}, at: [<ffffffff81277a84>] kbd_event+0x29/0x5b7
> 
> other info that might help us debug this:
>  Possible unsafe locking scenario:
> 
>        CPU0
>        ----
>   lock(kbd_event_lock);
>   lock(kbd_event_lock);
> 
>  *** DEADLOCK ***

Seems like I have actually hit this yesterday for real, so it's not just a 
theoretical scenario, see

	https://lkml.org/lkml/2012/4/30/90

-- 
Jiri Kosina
SUSE Labs

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