linux-kernel - Re: [PATCH v4 1/3] vt: fix check for system/busy console drivers when unregistering them

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Message-ID: <20141216073514.GG2711@phenom.ffwll.local>
Date:	Tue, 16 Dec 2014 08:35:14 +0100
From:	Daniel Vetter <daniel@...ll.ch>
To:	Imre Deak <imre.deak@...el.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Peter Hurley <peter@...leysoftware.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/3] vt: fix check for system/busy console drivers
 when unregistering them

On Tue, Dec 16, 2014 at 12:15:59AM +0200, Imre Deak wrote:
> The default console driver (conswitchp) and busy drivers bound to a
> console (as reported by con_is_bound()) shouldn't be unregistered.
> System console drivers (without the CON_DRIVER_FLAG_MODULE flag) can be
> unregistered, provided they are neither default nor busy. The current
> code checks for the CON_DRIVER_FLAG_INIT flag but this doesn't make
> sense: this flag is set for a driver whenever its associated console's
> con_startup() function is called, which first happens when the console
> driver is registered (so before the console gets bound) and gets cleared
> when the console gets unbound. The purpose of this flag is to show if we
> need to call con_startup() on a console before we use it.
> 
> Based on the above, do_unregister_con_driver() in its current form will
> allow unregistering a console driver only if it was never bound, but
> will refuse to unregister one that was bound and later unbound.
> 
> Fix this by dropping the CON_DRIVER_FLAG_INIT check, allowing
> unregistering of any console driver provided that it's not the default
> one and it's not busy.
> 
> v2:
> - reword the third paragraph to clarify how the fix works (Peter Hurley)
> v3:
> - unchanged
> v4:
> - Allow unregistering a system console driver too, needed by i915 to
>   unregister vgacon. Update commit description accordingly. (Daniel)
> 
> Signed-off-by: Imre Deak <imre.deak@...el.com>

You've successufully tricked me to again look at vt.c. Argh!!

Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>

> ---
>  drivers/tty/vt/vt.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index f3fbbbc..9c046fb 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -3665,8 +3665,7 @@ int do_unregister_con_driver(const struct consw *csw)
>  	for (i = 0; i < MAX_NR_CON_DRIVER; i++) {
>  		struct con_driver *con_driver = &registered_con_driver[i];
>  
> -		if (con_driver->con == csw &&
> -		    con_driver->flag & CON_DRIVER_FLAG_INIT) {
> +		if (con_driver->con == csw) {
>  			vtconsole_deinit_device(con_driver);
>  			device_destroy(vtconsole_class,
>  				       MKDEV(0, con_driver->node));
> -- 
> 1.8.4
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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