checkpatch: add warning for uses of printk_ratelimit

Warn about uses of printk_ratelimit() because it uses a global state and
can hide subsequent useful messages.

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Richard Weinberger <richard@nod.at>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -1943,6 +1943,11 @@ sub process {
 			WARN("LINUX_VERSION_CODE should be avoided, code should be for the version to which it is merged\n" . $herecurr);
 		}
 
+# check for uses of printk_ratelimit
+		if ($line =~ /\bprintk_ratelimit\s*\(/) {
+			WARN("Prefer printk_ratelimited or pr_<level>_ratelimited to printk_ratelimit\n" . $herecurr);
+		}
+
 # printk should use KERN_* levels.  Note that follow on printk's on the
 # same line do not need a level, so we use the current block context
 # to try and find and validate the current printk.  In summary the current