linux-kernel - Re: [PATCH] vt: Grab console_lock around con_is_bound in show

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Message-ID: <20190718103726.GA17341@ravnborg.org>
Date:   Thu, 18 Jul 2019 12:37:26 +0200
From:   Sam Ravnborg <sam@...nborg.org>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        Jens Remus <jremus@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-fbdev@...r.kernel.org, linux-s390@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Martin Hostettler <textshell@...uujin.de>,
        Adam Borowski <kilobyte@...band.pl>,
        Mikulas Patocka <mpatocka@...hat.com>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH] vt: Grab console_lock around con_is_bound in show_bind

Hi Daniel.

Patch looks good. You can add my:
Acked-by: Sam Ravnborg <sam@...nborg.org>

For good measure I checked all other users of con_is_bound()
and they looked good from a locking perspective.
Then I looked a bit more for missing locking and lost
the overview.

On Thu, Jul 18, 2019 at 10:09:03AM +0200, Daniel Vetter wrote:
> Not really harmful not to, but also not harm in grabbing the lock. And
> this shuts up a new WARNING I introduced in commit ddde3c18b700 ("vt:
> More locking checks").

Maybe add the warning that Jens reported to the changelog, in case
someone hits something that looks like this warning.
Mainly for google fodder, but also in case changelogs are searched.

	Sam
> 
> Reported-by: Jens Remus <jremus@...ux.ibm.com>
> Cc: linux-kernel@...r.kernel.org
> Cc: dri-devel@...ts.freedesktop.org
> Cc: linux-fbdev@...r.kernel.org
> Cc: linux-s390@...r.kernel.org
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Nicolas Pitre <nicolas.pitre@...aro.org>
> Cc: Martin Hostettler <textshell@...uujin.de>
> Cc: Adam Borowski <kilobyte@...band.pl>
> Cc: Mikulas Patocka <mpatocka@...hat.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>
> Cc: Daniel Vetter <daniel.vetter@...ll.ch>
> Cc: Sam Ravnborg <sam@...nborg.org>
> ---
>  drivers/tty/vt/vt.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index ec92f36ab5c4..34aa39d1aed9 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -3771,7 +3771,11 @@ static ssize_t show_bind(struct device *dev, struct device_attribute *attr,
>  			 char *buf)
>  {
>  	struct con_driver *con = dev_get_drvdata(dev);
> -	int bind = con_is_bound(con->con);
> +	int bind;
> +
> +	console_lock();
> +	bind = con_is_bound(con->con);
> +	console_unlock();
>  
>  	return snprintf(buf, PAGE_SIZE, "%i\n", bind);
>  }
> -- 
> 2.20.1