fbcon: use lock_fb_info in fbcon_open/release

Now we get to the real motiviation, because fbmem.c insists that
that's the right lock for these.

Ofc fbcon.c has a lot more places where it probably should call
lock_fb_info(). But looking at fbmem.c at least most of these seem to
be protected by console_lock() too, which is probably what papers over
any issues.

Note that this means we're shuffling around a bit the locking sections
for some of the console takeover and unbind paths, but not all:
- console binding/unbinding from the console layer never with
lock_fb_info
- unbind (as opposed to unlink) never bother with lock_fb_info

Also the real serialization against set_par and set_pan are still
doing by wrapping the entire ioctl code in console_lock(). So this
shuffling shouldn't be worse than what we had from a "can you trigger
races?" pov, but it's at least clearer.
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Claudio Suarez <cssk@net-c.es>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Du Cheng <ducheng2@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Zheyu Ma <zheyuma97@gmail.com>
Cc: Zhen Lei <thunder.leizhen@huawei.com>
Cc: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Link: https://patchwork.freedesktop.org/patch/msgid/20220405210335.3434130-13-daniel.vetter@ffwll.ch

drivers/video/fbdev/core/fbcon.c

@@ -684,8 +684,10 @@ static int fbcon_invalid_charcount(struct fb_info *info, unsigned charcount)
 
 static void fbcon_release(struct fb_info *info)
 {
+	lock_fb_info(info);
 	if (info->fbops->fb_release)
 		info->fbops->fb_release(info, 0);
+	unlock_fb_info(info);
 
 	module_put(info->fbops->owner);
 }
@@ -697,11 +699,14 @@ static int fbcon_open(struct fb_info *info)
 	if (!try_module_get(info->fbops->owner))
 		return -ENODEV;
 
+	lock_fb_info(info);
 	if (info->fbops->fb_open &&
 	    info->fbops->fb_open(info, 0)) {
+		unlock_fb_info(info);
 		module_put(info->fbops->owner);
 		return -ENODEV;
 	}
+	unlock_fb_info(info);
 
 	ops = kzalloc(sizeof(struct fbcon_ops), GFP_KERNEL);
 	if (!ops) {

drivers/video/fbdev/core/fbmem.c

@@ -1670,9 +1670,7 @@ static int do_register_framebuffer(struct fb_info *fb_info)
 		console_lock();
 	else
 		atomic_inc(&ignore_console_lock_warning);
-	lock_fb_info(fb_info);
 	ret = fbcon_fb_registered(fb_info);
-	unlock_fb_info(fb_info);
 
 	if (!lockless_register_fb)
 		console_unlock();
@@ -1689,9 +1687,7 @@ static void unbind_console(struct fb_info *fb_info)
 		return;
 
 	console_lock();
-	lock_fb_info(fb_info);
 	fbcon_fb_unbind(fb_info);
-	unlock_fb_info(fb_info);
 	console_unlock();
 }