fbdev/sysfs: Fix locking

fb_set_var requires we hold the fb_info lock. Or at least this now
matches what the ioctl does ...

Note that ps3fb and sh_mobile_lcdcfb are busted in different ways here,
but I will not fix them up.

Also in practice this isn't a big deal, because really variable fbdev
state is actually protected by console_lock (because fbcon just
doesn't bother with lock_fb_info() at all), and lock_fb_info
protecting anything is really just a neat lie. But that's a much
bigger fish to fry.
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Qing Wang <wangqing@vivo.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220405210335.3434130-6-daniel.vetter@ffwll.ch

drivers/video/fbdev/core/fbsysfs.c

@@ -91,9 +91,11 @@ static int activate(struct fb_info *fb_info, struct fb_var_screeninfo *var)
 
 	var->activate |= FB_ACTIVATE_FORCE;
 	console_lock();
+	lock_fb_info(fb_info);
 	err = fb_set_var(fb_info, var);
 	if (!err)
 		fbcon_update_vcs(fb_info, var->activate & FB_ACTIVATE_ALL);
+	unlock_fb_info(fb_info);
 	console_unlock();
 	if (err)
 		return err;