mm,oom: make oom_killer_disable() killable.

mm,oom: make oom_killer_disable() killable.

While oom_killer_disable() is called by freeze_processes() after all user
threads except the current thread are frozen, it is possible that kernel
threads invoke the OOM killer and sends SIGKILL to the current thread due
to sharing the thawed victim's memory.  Therefore, checking for SIGKILL is
preferable than TIF_MEMDIE.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>