checkpatch: warn on use of yield()

Using yield() is generally wrong.  Warn on its use.

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -3338,6 +3338,12 @@ sub process {
 			     "__func__ should be used instead of gcc specific __FUNCTION__\n"  . $herecurr);
 		}
 
+# check for use of yield()
+		if ($line =~ /\byield\s*\(\s*\)/) {
+			WARN("YIELD",
+			     "Using yield() is generally wrong. See yield() kernel-doc (sched/core.c)\n"  . $herecurr);
+		}
+
 # check for semaphores initialized locked
 		if ($line =~ /^.\s*sema_init.+,\W?0\W?\)/) {
 			WARN("CONSIDER_COMPLETION",