checkpatch: add warning on BUG/BUG_ON use

Using BUG/BUG_ON crashes the kernel and is just unfriendly.

Enable code that emits a warning on BUG/BUG_ON use.

Make the code emit the message at WARNING level when scanning a patch and
at CHECK level when scanning files so that script users don't feel an
obligation to fix code that might be above their pay grade.
Signed-off-by: Joe Perches <joe@perches.com>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -3448,13 +3448,15 @@ sub process {
 			}
 		}
 
-# # no BUG() or BUG_ON()
-# 		if ($line =~ /\b(BUG|BUG_ON)\b/) {
-# 			print "Try to use WARN_ON & Recovery code rather than BUG() or BUG_ON()\n";
-# 			print "$herecurr";
-# 			$clean = 0;
-# 		}
+# avoid BUG() or BUG_ON()
+		if ($line =~ /\b(?:BUG|BUG_ON)\b/) {
+			my $msg_type = \&WARN;
+			$msg_type = \&CHK if ($file);
+			&{$msg_type}("AVOID_BUG",
+				     "Avoid crashing the kernel - try using WARN_ON & recovery code rather than BUG() or BUG_ON()\n" . $herecurr);
+		}
 
+# avoid LINUX_VERSION_CODE
 		if ($line =~ /\bLINUX_VERSION_CODE\b/) {
 			WARN("LINUX_VERSION_CODE",
 			     "LINUX_VERSION_CODE should be avoided, code should be for the version to which it is merged\n" . $herecurr);