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Date:   Tue, 8 Feb 2022 19:27:32 +0100
From:   Sam Ravnborg <sam@ravnborg.org>
To:     DRI Development <dri-devel@lists.freedesktop.org>,
        linux-fbdev@vger.kernel.org, Du Cheng <ducheng2@gmail.com>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Claudio Suarez <cssk@net-c.es>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [PATCH 18/21] fbcon: untangle fbcon_exit
Message-ID: <YgK2FMXAkOQqQV4h@ravnborg.org>
References: <20220131210552.482606-1-daniel.vetter@ffwll.ch>
 <20220131210552.482606-19-daniel.vetter@ffwll.ch>
 <Yf2HTungn5DFhAPa@ravnborg.org>
 <YgJ2/f/JkKlyTJdh@phenom.ffwll.local>
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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>