kthread: add kerneldoc for kthread_create()

This macro is referenced in other kerneldoc comments, but lacks one of its
own; fix that.

Link: http://lkml.kernel.org/r/20160826072313.726a3485@lwn.net
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Reported-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/kthread.h

@@ -10,6 +10,17 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
 					   int node,
 					   const char namefmt[], ...);
 
+/**
+ * kthread_create - create a kthread on the current node
+ * @threadfn: the function to run in the thread
+ * @data: data pointer for @threadfn()
+ * @namefmt: printf-style format string for the thread name
+ * @...: arguments for @namefmt.
+ *
+ * This macro will create a kthread on the current node, leaving it in
+ * the stopped state.  This is just a helper for kthread_create_on_node();
+ * see the documentation there for more details.
+ */
 #define kthread_create(threadfn, data, namefmt, arg...) \
 	kthread_create_on_node(threadfn, data, NUMA_NO_NODE, namefmt, ##arg)