From cf4a3ae4ef3399179166a464af1d6b172225bef4 Mon Sep 17 00:00:00 2001 From: Daniel Vetter Date: Tue, 28 May 2019 11:02:47 +0200 Subject: fbdev: lock_fb_info cannot fail MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Ever since commit c47747fde931c02455683bd00ea43eaa62f35b0e Author: Linus Torvalds Date: Wed May 11 14:58:34 2011 -0700 fbmem: make read/write/ioctl use the frame buffer at open time fbdev has gained proper refcounting for the fbinfo attached to any open files, which means that the backing driver (stored in fb_info->fbops) cannot untimely disappear anymore. The only thing that can happen is that the entire device just outright disappears and gets unregistered, but file_fb_info does check for that. Except that it's racy - it only checks once at the start of a file_ops, there's no guarantee that the underlying fbdev won't untimely disappear. Aside: A proper way to fix that race is probably to replicate the srcu trickery we've rolled out in drm. But given that this race has existed since forever it's probably not one we need to fix right away. do_unregister_framebuffer also nowhere clears fb_info->fbops, hence the check in lock_fb_info can't possible catch a disappearing fbdev later on. Long story short: Ever since the above commit the fb_info->fbops checks have essentially become dead code. Remove this all. Aside from the file_ops callbacks, and stuff called from there there's only register/unregister code left. If that goes wrong a driver managed to register/unregister a device instance twice or in the wrong order. That's just a driver bug. v2: - fb_mmap had an open-coded version of the fbinfo->fops check, because it doesn't need the fbinfo->lock. Delete that too. - Use the wrapper function in fb_open/release now, since no difference anymore. Signed-off-by: Daniel Vetter Reviewed-by: Sam Ravnborg Reviewed-by: Maarten Lankhorst Cc: Bartlomiej Zolnierkiewicz Cc: Daniel Vetter Cc: Hans de Goede Cc: Yisheng Xie Cc: Sergey Senozhatsky Cc: "Noralf Trønnes" Cc: Peter Rosin Cc: "Michał Mirosław" Cc: Mikulas Patocka Cc: "Gustavo A. R. Silva" Cc: linux-fbdev@vger.kernel.org Link: https://patchwork.freedesktop.org/patch/msgid/20190528090304.9388-17-daniel.vetter@ffwll.ch --- include/linux/fb.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'include') diff --git a/include/linux/fb.h b/include/linux/fb.h index 288175fafaf6..aa8f18163151 100644 --- a/include/linux/fb.h +++ b/include/linux/fb.h @@ -663,7 +663,10 @@ extern struct class *fb_class; for (i = 0; i < FB_MAX; i++) \ if (!registered_fb[i]) {} else -extern int lock_fb_info(struct fb_info *info); +static inline void lock_fb_info(struct fb_info *info) +{ + mutex_lock(&info->lock); +} static inline void unlock_fb_info(struct fb_info *info) { -- cgit