Re: [PATCH 16/21] fbcon: Move console_lock for register/unlink/unregister

[Daniel Vetter]

On Fri, Feb 04, 2022 at 08:54:24PM +0100, Sam Ravnborg wrote:
> Hi Daniel.
> 
> On Mon, Jan 31, 2022 at 10:05:47PM +0100, Daniel Vetter wrote:
> > Ideally console_lock becomes an implementation detail of fbcon.c and
> > doesn't show up anywhere in fbmem.c. We're still pretty far from that,
> > but at least the register/unregister code is there now.
> > 
> > With this the do_fb_ioctl() handler is the only code in fbmem.c still
> > calling console_lock().
> > 
> > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> > Cc: Daniel Vetter <daniel@xxxxxxxx>
> > Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
> > Cc: Du Cheng <ducheng2@xxxxxxxxx>
> > Cc: Claudio Suarez <cssk@xxxxxxxx>
> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> > Cc: Sam Ravnborg <sam@xxxxxxxxxxxx>
> > Cc: Zheyu Ma <zheyuma97@xxxxxxxxx>
> > Cc: Guenter Roeck <linux@xxxxxxxxxxxx>
> > Cc: Alex Deucher <alexander.deucher@xxxxxxx>
> > Cc: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
> > Cc: Xiyu Yang <xiyuyang19@xxxxxxxxxxxx>
> 
> Like how lock_console is now almost local to fbcon.
> Except the usage outside fbmem + fbcon taht is.

Yeah that's the goal. The problem is that moving console_lock for the
remaining fb_pan and fb_set_var calls will mean we need to put
lock_fbinfo() calls into fbcon.c, and right now that's just not
impossible. The FIXME update at the end of the series tries to explain
this a bit more.
-Daniel

> 
> Acked-by: Sam Ravnborg <sam@xxxxxxxxxxxx>
> 
> > ---
> >  drivers/video/fbdev/core/fbcon.c | 33 ++++++++++++++++++++++++++------
> >  drivers/video/fbdev/core/fbmem.c | 23 ++--------------------
> >  2 files changed, 29 insertions(+), 27 deletions(-)
> > 
> > diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> > index 11b9f962af6f..e5e8aaf6f60d 100644
> > --- a/drivers/video/fbdev/core/fbcon.c
> > +++ b/drivers/video/fbdev/core/fbcon.c
> > @@ -2776,10 +2776,12 @@ void fbcon_fb_unbind(struct fb_info *info)
> >  	int i, new_idx = -1;
> >  	int idx = info->node;
> >  
> > -	WARN_CONSOLE_UNLOCKED();
> > +	console_lock();
> >  
> > -	if (!fbcon_has_console_bind)
> > +	if (!fbcon_has_console_bind) {
> > +		console_unlock();
> >  		return;
> > +	}
> >  
> >  	for (i = first_fb_vc; i <= last_fb_vc; i++) {
> >  		if (con2fb_map[i] != idx &&
> > @@ -2814,6 +2816,8 @@ void fbcon_fb_unbind(struct fb_info *info)
> >  		}
> >  		fbcon_unbind();
> >  	}
> > +
> > +	console_unlock();
> >  }
> >  
> >  /* called with console_lock held */
> > @@ -2821,10 +2825,12 @@ void fbcon_fb_unregistered(struct fb_info *info)
> >  {
> >  	int i, idx;
> >  
> > -	WARN_CONSOLE_UNLOCKED();
> > +	console_lock();
> >  
> > -	if (deferred_takeover)
> > +	if (deferred_takeover) {
> > +		console_unlock();
> >  		return;
> > +	}
> >  
> >  	idx = info->node;
> >  	for (i = first_fb_vc; i <= last_fb_vc; i++) {
> > @@ -2853,6 +2859,7 @@ void fbcon_fb_unregistered(struct fb_info *info)
> >  
> >  	if (!num_registered_fb)
> >  		do_unregister_con_driver(&fb_con);
> > +	console_unlock();
> >  }
> >  
> >  void fbcon_remap_all(struct fb_info *info)
> > @@ -2910,19 +2917,27 @@ static inline void fbcon_select_primary(struct fb_info *info)
> >  }
> >  #endif /* CONFIG_FRAMEBUFFER_DETECT_PRIMARY */
> >  
> > +static bool lockless_register_fb;
> > +module_param_named_unsafe(lockless_register_fb, lockless_register_fb, bool, 0400);
> > +MODULE_PARM_DESC(lockless_register_fb,
> > +	"Lockless framebuffer registration for debugging [default=off]");
> > +
> >  /* called with console_lock held */
> >  int fbcon_fb_registered(struct fb_info *info)
> >  {
> >  	int ret = 0, i, idx;
> >  
> > -	WARN_CONSOLE_UNLOCKED();
> > +	if (!lockless_register_fb)
> > +		console_lock();
> > +	else
> > +		atomic_inc(&ignore_console_lock_warning);
> >  
> >  	idx = info->node;
> >  	fbcon_select_primary(info);
> >  
> >  	if (deferred_takeover) {
> >  		pr_info("fbcon: Deferring console take-over\n");
> > -		return 0;
> > +		goto out;
> >  	}
> >  
> >  	if (info_idx == -1) {
> > @@ -2942,6 +2957,12 @@ int fbcon_fb_registered(struct fb_info *info)
> >  		}
> >  	}
> >  
> > +out:
> > +	if (!lockless_register_fb)
> > +		console_unlock();
> > +	else
> > +		atomic_dec(&ignore_console_lock_warning);
> > +
> >  	return ret;
> >  }
> >  
> > diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
> > index fd51d12f2702..904ef1250677 100644
> > --- a/drivers/video/fbdev/core/fbmem.c
> > +++ b/drivers/video/fbdev/core/fbmem.c
> > @@ -1573,14 +1573,9 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a,
> >  	}
> >  }
> >  
> > -static bool lockless_register_fb;
> > -module_param_named_unsafe(lockless_register_fb, lockless_register_fb, bool, 0400);
> > -MODULE_PARM_DESC(lockless_register_fb,
> > -	"Lockless framebuffer registration for debugging [default=off]");
> > -
> >  static int do_register_framebuffer(struct fb_info *fb_info)
> >  {
> > -	int i, ret;
> > +	int i;
> >  	struct fb_videomode mode;
> >  
> >  	if (fb_check_foreignness(fb_info))
> > @@ -1649,17 +1644,7 @@ static int do_register_framebuffer(struct fb_info *fb_info)
> >  	}
> >  #endif
> >  
> > -	if (!lockless_register_fb)
> > -		console_lock();
> > -	else
> > -		atomic_inc(&ignore_console_lock_warning);
> > -	ret = fbcon_fb_registered(fb_info);
> > -
> > -	if (!lockless_register_fb)
> > -		console_unlock();
> > -	else
> > -		atomic_dec(&ignore_console_lock_warning);
> > -	return ret;
> > +	return fbcon_fb_registered(fb_info);
> >  }
> >  
> >  static void unbind_console(struct fb_info *fb_info)
> > @@ -1669,9 +1654,7 @@ static void unbind_console(struct fb_info *fb_info)
> >  	if (WARN_ON(i < 0 || i >= FB_MAX || registered_fb[i] != fb_info))
> >  		return;
> >  
> > -	console_lock();
> >  	fbcon_fb_unbind(fb_info);
> > -	console_unlock();
> >  }
> >  
> >  static void unlink_framebuffer(struct fb_info *fb_info)
> > @@ -1714,9 +1697,7 @@ static void do_unregister_framebuffer(struct fb_info *fb_info)
> >  		fb_notifier_call_chain(FB_EVENT_FB_UNREGISTERED, &event);
> >  	}
> >  #endif
> > -	console_lock();
> >  	fbcon_fb_unregistered(fb_info);
> > -	console_unlock();
> >  
> >  	/* this may free fb info */
> >  	put_fb_info(fb_info);
> > -- 
> > 2.33.0

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch