kthread: fix return value of kthread_create() upon SIGKILL.

Commit 786235ee ("kthread: make kthread_create() killable") meant
for allowing kthread_create() to abort as soon as killed by the
OOM-killer.  But returning -ENOMEM is wrong if killed by SIGKILL from
userspace.  Change kthread_create() to return -EINTR upon SIGKILL.
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Oleg Nesterov <oleg@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: <stable@vger.kernel.org> [3.13+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/kthread.c

@@ -262,7 +262,7 @@ static void create_kthread(struct kthread_create_info *create)
  * kthread_stop() has been called).  The return value should be zero
  * or a negative error number; it will be passed to kthread_stop().
  *
- * Returns a task_struct or ERR_PTR(-ENOMEM).
+ * Returns a task_struct or ERR_PTR(-ENOMEM) or ERR_PTR(-EINTR).
  */
 struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
 					   void *data, int node,
@@ -298,7 +298,7 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
 		 * that thread.
 		 */
 		if (xchg(&create->done, NULL))
-			return ERR_PTR(-ENOMEM);
+			return ERR_PTR(-EINTR);
 		/*
 		 * kthreadd (or new kernel thread) will call complete()
 		 * shortly.