fbmem: fix fb_info->lock and mm->mmap_sem circular locking dependency
Fix a circular locking dependency in the frame buffer console driver
pushing down the mutex fb_info->lock.
Circular locking dependecies occur calling the blocking
fb_notifier_call_chain() with fb_info->lock held. Notifier callbacks can
try to acquire mm->mmap_sem, while fb_mmap() acquires the locks in the
reverse order mm->mmap_sem => fb_info->lock.
Tested-by: Andrey Borzenkov <arvidjaar@mail.ru>
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
index cfd9dce..b64f061 100644
--- a/drivers/video/fbmem.c
+++ b/drivers/video/fbmem.c
@@ -1086,13 +1086,8 @@
return -EINVAL;
con2fb.framebuffer = -1;
event.data = &con2fb;
-
- if (!lock_fb_info(info))
- return -ENODEV;
event.info = info;
fb_notifier_call_chain(FB_EVENT_GET_CONSOLE_MAP, &event);
- unlock_fb_info(info);
-
ret = copy_to_user(argp, &con2fb, sizeof(con2fb)) ? -EFAULT : 0;
break;
case FBIOPUT_CON2FBMAP:
@@ -1109,12 +1104,8 @@
break;
}
event.data = &con2fb;
- if (!lock_fb_info(info))
- return -ENODEV;
event.info = info;
- ret = fb_notifier_call_chain(FB_EVENT_SET_CONSOLE_MAP,
- &event);
- unlock_fb_info(info);
+ ret = fb_notifier_call_chain(FB_EVENT_SET_CONSOLE_MAP, &event);
break;
case FBIOBLANK:
if (!lock_fb_info(info))