From cf4a3ae4ef3399179166a464af1d6b172225bef4 Mon Sep 17 00:00:00 2001 From: Daniel Vetter Date: Tue, 28 May 2019 11:02:47 +0200 Subject: [PATCH] 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 --- drivers/video/fbdev/core/fbcmap.c | 6 +-- drivers/video/fbdev/core/fbcon.c | 3 +- drivers/video/fbdev/core/fbmem.c | 73 +++++++------------------------ include/linux/fb.h | 5 ++- 4 files changed, 23 insertions(+), 64 deletions(-) diff --git a/drivers/video/fbdev/core/fbcmap.c b/drivers/video/fbdev/core/fbcmap.c index 2811c4afde01..e5ae33c1a8e8 100644 --- a/drivers/video/fbdev/core/fbcmap.c +++ b/drivers/video/fbdev/core/fbcmap.c @@ -285,11 +285,7 @@ int fb_set_user_cmap(struct fb_cmap_user *cmap, struct fb_info *info) goto out; } umap.start = cmap->start; - if (!lock_fb_info(info)) { - rc = -ENODEV; - goto out; - } - + lock_fb_info(info); rc = fb_set_cmap(&umap, info); unlock_fb_info(info); out: diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c index c12fc98035e0..f7f3eb0f1893 100644 --- a/drivers/video/fbdev/core/fbcon.c +++ b/drivers/video/fbdev/core/fbcon.c @@ -2364,8 +2364,7 @@ static void fbcon_generic_blank(struct vc_data *vc, struct fb_info *info, } - if (!lock_fb_info(info)) - return; + lock_fb_info(info); event.info = info; event.data = ␣ fb_notifier_call_chain(FB_EVENT_CONBLANK, &event); diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index bed7698ad18a..d73762324ca2 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -80,17 +80,6 @@ static void put_fb_info(struct fb_info *fb_info) fb_info->fbops->fb_destroy(fb_info); } -int lock_fb_info(struct fb_info *info) -{ - mutex_lock(&info->lock); - if (!info->fbops) { - mutex_unlock(&info->lock); - return 0; - } - return 1; -} -EXPORT_SYMBOL(lock_fb_info); - /* * Helpers */ @@ -1121,8 +1110,7 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, switch (cmd) { case FBIOGET_VSCREENINFO: - if (!lock_fb_info(info)) - return -ENODEV; + lock_fb_info(info); var = info->var; unlock_fb_info(info); @@ -1132,10 +1120,7 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, if (copy_from_user(&var, argp, sizeof(var))) return -EFAULT; console_lock(); - if (!lock_fb_info(info)) { - console_unlock(); - return -ENODEV; - } + lock_fb_info(info); info->flags |= FBINFO_MISC_USEREVENT; ret = fb_set_var(info, &var); info->flags &= ~FBINFO_MISC_USEREVENT; @@ -1145,8 +1130,7 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, ret = -EFAULT; break; case FBIOGET_FSCREENINFO: - if (!lock_fb_info(info)) - return -ENODEV; + lock_fb_info(info); fix = info->fix; if (info->flags & FBINFO_HIDE_SMEM_START) fix.smem_start = 0; @@ -1162,8 +1146,7 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, case FBIOGETCMAP: if (copy_from_user(&cmap, argp, sizeof(cmap))) return -EFAULT; - if (!lock_fb_info(info)) - return -ENODEV; + lock_fb_info(info); cmap_from = info->cmap; unlock_fb_info(info); ret = fb_cmap_to_user(&cmap_from, &cmap); @@ -1172,10 +1155,7 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, if (copy_from_user(&var, argp, sizeof(var))) return -EFAULT; console_lock(); - if (!lock_fb_info(info)) { - console_unlock(); - return -ENODEV; - } + lock_fb_info(info); ret = fb_pan_display(info, &var); unlock_fb_info(info); console_unlock(); @@ -1192,8 +1172,7 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, return -EINVAL; con2fb.framebuffer = -1; event.data = &con2fb; - if (!lock_fb_info(info)) - return -ENODEV; + lock_fb_info(info); event.info = info; fb_notifier_call_chain(FB_EVENT_GET_CONSOLE_MAP, &event); unlock_fb_info(info); @@ -1214,10 +1193,7 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, } event.data = &con2fb; console_lock(); - if (!lock_fb_info(info)) { - console_unlock(); - return -ENODEV; - } + lock_fb_info(info); event.info = info; ret = fb_notifier_call_chain(FB_EVENT_SET_CONSOLE_MAP, &event); unlock_fb_info(info); @@ -1225,10 +1201,7 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, break; case FBIOBLANK: console_lock(); - if (!lock_fb_info(info)) { - console_unlock(); - return -ENODEV; - } + lock_fb_info(info); info->flags |= FBINFO_MISC_USEREVENT; ret = fb_blank(info, arg); info->flags &= ~FBINFO_MISC_USEREVENT; @@ -1236,8 +1209,7 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, console_unlock(); break; default: - if (!lock_fb_info(info)) - return -ENODEV; + lock_fb_info(info); fb = info->fbops; if (fb->fb_ioctl) ret = fb->fb_ioctl(info, cmd, arg); @@ -1357,8 +1329,7 @@ static int fb_get_fscreeninfo(struct fb_info *info, unsigned int cmd, { struct fb_fix_screeninfo fix; - if (!lock_fb_info(info)) - return -ENODEV; + lock_fb_info(info); fix = info->fix; if (info->flags & FBINFO_HIDE_SMEM_START) fix.smem_start = 0; @@ -1418,8 +1389,6 @@ fb_mmap(struct file *file, struct vm_area_struct * vma) if (!info) return -ENODEV; fb = info->fbops; - if (!fb) - return -ENODEV; mutex_lock(&info->mm_lock); if (fb->fb_mmap) { int res; @@ -1483,7 +1452,7 @@ __releases(&info->lock) if (IS_ERR(info)) return PTR_ERR(info); - mutex_lock(&info->lock); + lock_fb_info(info); if (!try_module_get(info->fbops->owner)) { res = -ENODEV; goto out; @@ -1499,7 +1468,7 @@ __releases(&info->lock) fb_deferred_io_open(info, inode, file); #endif out: - mutex_unlock(&info->lock); + unlock_fb_info(info); if (res) put_fb_info(info); return res; @@ -1512,11 +1481,11 @@ __releases(&info->lock) { struct fb_info * const info = file->private_data; - mutex_lock(&info->lock); + lock_fb_info(info); if (info->fbops->fb_release) info->fbops->fb_release(info,1); module_put(info->fbops->owner); - mutex_unlock(&info->lock); + unlock_fb_info(info); put_fb_info(info); return 0; } @@ -1734,14 +1703,10 @@ static int do_register_framebuffer(struct fb_info *fb_info) console_lock(); else atomic_inc(&ignore_console_lock_warning); - if (!lock_fb_info(fb_info)) { - ret = -ENODEV; - goto unlock_console; - } - + lock_fb_info(fb_info); ret = fbcon_fb_registered(fb_info); unlock_fb_info(fb_info); -unlock_console: + if (!lockless_register_fb) console_unlock(); else @@ -1759,11 +1724,7 @@ static int unbind_console(struct fb_info *fb_info) return -EINVAL; console_lock(); - if (!lock_fb_info(fb_info)) { - console_unlock(); - return -ENODEV; - } - + lock_fb_info(fb_info); event.info = fb_info; ret = fb_notifier_call_chain(FB_EVENT_FB_UNBIND, &event); unlock_fb_info(fb_info); 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) {