setquota acquired semaphore s_umount for read and then tried to perform a
transaction (and waits because the device is suspended). dmsetup resume tries
to acquire s_umount for write before resuming the device (and waits for
setquota).
Fix the deadlock by grabbing a thawed superblock for quota commands which need
it.
Reported-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Jan Kara <jack@suse.cz> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>