Re: [PATCH v5 2/3] fbcon: Call WARN_CONSOLE_UNLOCKED() where applicable

[Hans de Goede]

Hi,

On 11-07-18 16:52, Steven Rostedt wrote:
> On Wed, 11 Jul 2018 16:46:11 +0200
> Thomas Zimmermann <tzimmermann@xxxxxxx> 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?

Yes I'm already preparing a patch like that :)

Without the unlikely though, this is not used in hot paths.

Regards,

Hans



> -- Steve
>
>
> > Best regards
> > Thomas
> >
> > > Acked-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> > > Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> > > Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
> > > Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
> > > ---
> > > 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);
> > >