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 <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

scripts/checkpatch.pl

···
 			}
 		}
 
+# 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";