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

[Hans de Goede]

Hi,

On 11-07-18 17:28, Daniel Vetter wrote:
> On Wed, Jul 11, 2018 at 5:14 PM, Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
> > Hi,
> >
> > On 11-07-18 17:07, Thomas Zimmermann wrote:
> > > Hi
> > >
> > > Am 11.07.2018 um 16:52 schrieb Steven Rostedt:
> > > > What if you make lockless_register_fb visible to fbcon, and then we can
> > > > have a macro:
> > >
> > >
> > > There are more of these macro invocations under drivers/tty/vt, which
> > > also mess up the log during debugging.
> >
> >
> > Hmm, so this option is already broken (in a way) then, my first reaction
> > to your mail was that we should just remove that option. But that seemed
> > a bit harsh to me so I've been working on a fix for the last 10 minutes
> > or so.
> >
> > But if it is already broken I'm tempted to just remove the option and
> > be done with it.  We really need less cruft in the fbdev/fbcon code not
> > more.
>
> Please don't remove it, it makes debugging kms driver issues on
> initial modeset (which is usually run from framebuffer_register, while
> hodling the console_lock) impossible.

OK, so if we don't remove it, we should probably make it so that it
can be used without triggering any WARN_ONs, which would require changing
the existing WARN_CONSOLE_UNLOCKED() so that the calls from drivers/tty/vt/vt.c
also do not trigger it ?

I guess one can just ignore the oopses when debugging, but debugging surely
would be easier if there are just no oopses ?

Regards,

Hans




> -Daniel
>
> > > WARN_CONSOLE_UNLOCKED is already protected by an '#ifdef 1 ... #else
> > > ...' construct [1]. I thought about turning this into a config option.
> >
> >
> > Ah I noticed the #if but I did not notice that it was a "#if 1".
> >
> > If you want to fix lockless_register_fb it really should be replaced
> > with a runtime check, not a Kconfig option. This would require having
> > some lockless variable in the console code itself, which then gets
> > set by the fbdev code during init based on its lockless_register_fb
> > setting.
> >
> > But as said I think we should seriously consider just removing
> > lockless_register_fb.
> >
> > Regards,
> >
> > Hans
> >
> >
> >
> >
> >
> >
> >
> > > Best regards
> > > Thomas
> > >
> > > [1]
> > >
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/console.h#n203
> > >
> > > > #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@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);
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