linux-kernel - Re: [PATCH v5 2/3] fbcon: Call WARN_CONSOLE

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Message-ID: <20180711105255.32803a3c@gandalf.local.home>
Date:   Wed, 11 Jul 2018 10:52:55 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Thomas Zimmermann <tzimmermann@...e.de>
Cc:     Hans de Goede <hdegoede@...hat.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 2/3] fbcon: Call WARN_CONSOLE_UNLOCKED() where
 applicable

On Wed, 11 Jul 2018 16:46:11 +0200
Thomas Zimmermann <tzimmermann@...e.de> wrote:

> Hi
> 
> Am 28.06.2018 um 11:03 schrieb Hans de Goede:
> > Replace comments about places where the console lock should be held with
> > calls to WARN_CONSOLE_UNLOCKED() to assert that it is actually held.  
> 
> Debugging fbcon sometimes requires to not take the console lock. This
> patch breaks the debugging workaround provided by
> 'fb.lockless_register_fb'. The dmesg is now filled with warnings about
> the missing lock.
> 

What if you make lockless_register_fb visible to fbcon, and then we can
have a macro:

#define WARN_FB_CONSOLE_UNLOCKED() 			\
	do {						\
		if (unlikely(!lockless_register_fb))	\
			WARN_CONSOLE_UNLOCKED();	\
	} while (0)

And use that instead?

-- Steve


> Best regards
> Thomas
> 
> > Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> > Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
> > Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> > Signed-off-by: Hans de Goede <hdegoede@...hat.com>
> > ---
> > Changes in v3:
> > -New patch in v3 of this patchset
> >
> > Changes in v4:
> > -Keep the comments about which fbcon functions need locks in place
> > ---
> >  drivers/video/fbdev/core/fbcon.c | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> >
> > diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> > index c910e74d46ff..cd8d52a967aa 100644
> > --- a/drivers/video/fbdev/core/fbcon.c
> > +++ b/drivers/video/fbdev/core/fbcon.c
> > @@ -828,6 +828,8 @@ static int set_con2fb_map(int unit, int newidx, int user)
> >  	struct fb_info *oldinfo = NULL;
> >   	int found, err = 0;
> >  
> > +	WARN_CONSOLE_UNLOCKED();
> > +
> >  	if (oldidx == newidx)
> >  		return 0;
> >  
> > @@ -3044,6 +3046,8 @@ static int fbcon_fb_unbind(int idx)
> >  {
> >  	int i, new_idx = -1, ret = 0;
> >  
> > +	WARN_CONSOLE_UNLOCKED();
> > +
> >  	if (!fbcon_has_console_bind)
> >  		return 0;
> >  
> > @@ -3094,6 +3098,8 @@ static int fbcon_fb_unregistered(struct fb_info *info)
> >  {
> >  	int i, idx;
> >  
> > +	WARN_CONSOLE_UNLOCKED();
> > +
> >  	idx = info->node;
> >  	for (i = first_fb_vc; i <= last_fb_vc; i++) {
> >  		if (con2fb_map[i] == idx)
> > @@ -3131,6 +3137,9 @@ static int fbcon_fb_unregistered(struct fb_info *info)
> >  static void fbcon_remap_all(int idx)
> >  {
> >  	int i;
> > +
> > +	WARN_CONSOLE_UNLOCKED();
> > +
> >  	for (i = first_fb_vc; i <= last_fb_vc; i++)
> >  		set_con2fb_map(i, idx, 0);
> >  
> > @@ -3177,6 +3186,8 @@ static int fbcon_fb_registered(struct fb_info *info)
> >  {
> >  	int ret = 0, i, idx;
> >  
> > +	WARN_CONSOLE_UNLOCKED();
> > +
> >  	idx = info->node;
> >  	fbcon_select_primary(info);
> >    
>