Re: [Intel-gfx] [PATCH 18/21] fbcon: untangle fbcon_exit

Sam Ravnborg
2022-02-08T18:27:43Z

On Tue, Feb 08, 2022 at 02:58:21PM +0100, Daniel Vetter wrote:
> On Fri, Feb 04, 2022 at 09:06:38PM +0100, Sam Ravnborg wrote:
> > Hi Daniel,
> >
> > On Mon, Jan 31, 2022 at 10:05:49PM +0100, Daniel Vetter wrote:
> > > There's a bunch of confusions going on here:
> > > - The deferred fbcon setup notifier should only be cleaned up from
> > > fb_console_exit(), to be symmetric with fb_console_init()
> > > - We also need to make sure we don't race with the work, which means
> > > temporarily dropping the console lock (or we can deadlock)
> > > - That also means no point in clearing deferred_takeover, we are
> > > unloading everything anyway.
> > > - Finally rename fbcon_exit to fbcon_release_all and move it, since
> > > that's what's it doing when being called from consw->con_deinit
> > > through fbcon_deinit.
> > >
> > > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > > Cc: Daniel Vetter <daniel@ffwll.ch>
> > > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > > Cc: Claudio Suarez <cssk@net-c.es>
> > > Cc: Du Cheng <ducheng2@gmail.com>
> > > Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > > ---
> > > drivers/video/fbdev/core/fbcon.c | 63 ++++++++++++++++----------------
> > > 1 file changed, 32 insertions(+), 31 deletions(-)
> > >
> > > diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> > > index 5c14e24d14a1..22581952b4fd 100644
> > > --- a/drivers/video/fbdev/core/fbcon.c
> > > +++ b/drivers/video/fbdev/core/fbcon.c
> > > @@ -185,7 +185,6 @@ static void fbcon_set_disp(struct fb_info *info, struct fb_var_screeninfo *var,
> > > int unit);
> > > static void fbcon_modechanged(struct fb_info *info);
> > > static void fbcon_set_all_vcs(struct fb_info *info);
> > > -static void fbcon_exit(void);
> > >
> > > static struct device *fbcon_device;
> > >
> > > @@ -1149,6 +1148,27 @@ static void fbcon_free_font(struct fbcon_display *p, bool freefont)
> > >
> > > static void set_vc_hi_font(struct vc_data *vc, bool set);
> > >
> > > +static void fbcon_release_all(void)
> > > +{
> > > + struct fb_info *info;
> > > + int i, j, mapped;
> > > +
> > > + for_each_registered_fb(i) {
> > > + mapped = 0;
> > > + info = registered_fb[i];
> > > +
> > > + for (j = first_fb_vc; j <= last_fb_vc; j++) {
> > > + if (con2fb_map[j] == i) {
> > > + mapped = 1;
> > > + con2fb_map[j] = -1;
> > > + }
> > > + }
> > > +
> > > + if (mapped)
> > > + fbcon_release(info);
> > > + }
> > > +}
> > > +
> > > static void fbcon_deinit(struct vc_data *vc)
> > > {
> > > struct fbcon_display *p = &fb_display[vc->vc_num];
> > > @@ -1188,7 +1208,7 @@ static void fbcon_deinit(struct vc_data *vc)
> > > set_vc_hi_font(vc, false);
> > >
> > > if (!con_is_bound(&fb_con))
> > > - fbcon_exit();
> > > + fbcon_release_all();
> > >
> > > if (vc->vc_num == logo_shown)
> > > logo_shown = FBCON_LOGO_CANSHOW;
> > > @@ -3316,34 +3336,6 @@ static void fbcon_start(void)
> > > #endif
> > > }
> > >
> > > -static void fbcon_exit(void)
> > > -{
> > > - struct fb_info *info;
> > > - int i, j, mapped;
> > > -
> > > -#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
> > > - if (deferred_takeover) {
> > > - dummycon_unregister_output_notifier(&fbcon_output_nb);
> > > - deferred_takeover = false;
> > > - }
> > > -#endif
> > > -
> > > - for_each_registered_fb(i) {
> > > - mapped = 0;
> > > - info = registered_fb[i];
> > > -
> > > - for (j = first_fb_vc; j <= last_fb_vc; j++) {
> > > - if (con2fb_map[j] == i) {
> > > - mapped = 1;
> > > - con2fb_map[j] = -1;
> > > - }
> > > - }
> > > -
> > > - if (mapped)
> > > - fbcon_release(info);
> > > - }
> > > -}
> > > -
> > > void __init fb_console_init(void)
> > > {
> > > int i;
> > > @@ -3383,10 +3375,19 @@ static void __exit fbcon_deinit_device(void)
> > >
> > > void __exit fb_console_exit(void)
> > > {
> > > +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
> > > + console_lock();
> > > + if (deferred_takeover)
> > > + dummycon_unregister_output_notifier(&fbcon_output_nb);
> > > + console_unlock();
> > > +
> > > + cancel_work_sync(&fbcon_deferred_takeover_work);
> > > +#endif
> > > +
> > > console_lock();
> > > fbcon_deinit_device();
> > > device_destroy(fb_class, MKDEV(0, 0));
> > > - fbcon_exit();
> > > +
> > We loose the call to fbcon_release_all() here.
> > We have part of the old fbcon_exit() above, but miss the release parts.
> >
> > Maybe I missed something obvious?
>
> Ah yes that's the entire point of this change. The release_all in the
> fbcon exit path was only needed when fbcon was a separate module
> indepedent from core fb.ko. Which means it was possible to unload fbcon
> while having fbdev drivers registered.
>
> But since we've merged them that has become impossible, so by the time the
> fb.ko module can be unloaded, there's guaranteed to be no fbdev drivers
> left. And hence removing them is pointless.
Makes sense, thanks for the explanation.

>
> Ack with that explainer added to the commit message?
Yes, then it is
Acked-by: Sam Ravnborg <sam@ravnborg.org>