Fix a possible though highly unlikely deadlock:
Thread A: Thread B:
- acquire mmap_sem - dv1394_ioctl/read/write()
- dv1394_mmap() - acquire video->mtx
- acquire video->mtx - copy_to/from_user(), possible page fault:
acquire mmap_sem
The simplest fix is to use mutex_trylock() instead of mutex_lock() in
dv1394_mmap(). This changes the behavior under contention in a way
which is visible to userspace clients. However, my guess is that no
clients exist which use mmap vs. ioctl/read/write on the dv1394
character device file interface in concurrent threads.
Reported-by: Johannes Weiner <hannes@saeurebad.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
8449fc3ae5