Prevents hung_task detector from panicing the machine. This is also
needed to prevent this wait from blocking suspend.

(It doesnt' currently block suspend but it would once the next
patch in this series is applied.)

[yongjun_wei@trendmicro.com.cn: kernel/exit.c: remove duplicated include]
Signed-off-by: NMandeep Singh Baines <msb@chromium.org>
Cc: Ben Chan <benchan@chromium.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>