fbdev: fix info->lock deadlock in fbcon_event_notify()

fb_notifier_call_chain() is called with info->lock held, i.e.  in
do_fb_ioctl() => FBIOPUT_VSCREENINFO => fb_set_var() and the some
notifier callbacks, like fbcon_event_notify(), try to re-acquire
info->lock again.

Remove the lock/unlock_fb_info() in all the framebuffer notifier
callbacks' and be sure to always call fb_notifier_call_chain() with
info->lock held.

Reported-by: Pavel Roskin <proski@gnu.org>
Reported-by: Eric Miao <eric.y.miao@gmail.com>
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>
Cc: Stefan Richter <stefanr@s5r6.in-berlin.de>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 0 insertions, 6 deletions

diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
index dd37cbcaf8ce..157057c79ca3 100644
--- a/drivers/video/backlight/backlight.c
+++ b/drivers/video/backlight/backlight.c
@@ -35,8 +35,6 @@ static int fb_notifier_callback(struct notifier_block *self,
 		return 0;
 
 	bd = container_of(self, struct backlight_device, fb_notif);
-	if (!lock_fb_info(evdata->info))
-		return -ENODEV;
 	mutex_lock(&bd->ops_lock);
 	if (bd->ops)
 		if (!bd->ops->check_fb ||
@@ -49,7 +47,6 @@ static int fb_notifier_callback(struct notifier_block *self,
 			backlight_update_status(bd);
 		}
 	mutex_unlock(&bd->ops_lock);
-	unlock_fb_info(evdata->info);
 	return 0;
 }
 
diff --git a/drivers/video/backlight/lcd.c b/drivers/video/backlight/lcd.c
index 0bb13df0fa89..b6449470106c 100644
--- a/drivers/video/backlight/lcd.c
+++ b/drivers/video/backlight/lcd.c
@@ -40,8 +40,6 @@ static int fb_notifier_callback(struct notifier_block *self,
 	if (!ld->ops)
 		return 0;
 
-	if (!lock_fb_info(evdata->info))
-		return -ENODEV;
 	mutex_lock(&ld->ops_lock);
 	if (!ld->ops->check_fb || ld->ops->check_fb(ld, evdata->info)) {
 		if (event == FB_EVENT_BLANK) {
@@ -53,7 +51,6 @@ static int fb_notifier_callback(struct notifier_block *self,
 		}
 	}
 	mutex_unlock(&ld->ops_lock);
-	unlock_fb_info(evdata->info);
 	return 0;
 }