checkpatch: warn about unexpectedly long msleep's

As explained in Documentation/timers/timers-howto.txt, msleep's of < 20ms
may sleep for as long as 20ms.  Caller's of msleep(1) or msleep(2), etc
are likely not to expect this quirky behavior - warn them.

Signed-off-by: Patrick Pannuto <ppannuto@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -2592,6 +2592,13 @@ sub process {
 			}
 		}
 
+# warn about unexpectedly long msleep's
+		if ($line =~ /\bmsleep\s*\((\d+)\);/) {
+			if ($1 < 20) {
+				WARN("msleep < 20ms can sleep for up to 20ms; see Documentation/timers/timers-howto.txt\n" . $line);
+			}
+		}
+
 # warn about #ifdefs in C files
 #		if ($line =~ /^.\s*\#\s*if(|n)def/ && ($realfile =~ /\.c$/)) {
 #			print "#ifdef in C files should be avoided\n";