checkpatch: add a --strict test for comparison to true/false

Comparing to true or false is error prone.

Add tests for the various forms of (foo == true) && (false != bar)
that are only reported with --strict.
Signed-off-by: NJoe Perches <joe@perches.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -3588,6 +3588,33 @@ sub process {
 			     "Using yield() is generally wrong. See yield() kernel-doc (sched/core.c)\n"  . $herecurr);
 		}
 
+# check for comparisons against true and false
+		if ($line =~ /\+\s*(.*?)\b(true|false|$Lval)\s*(==|\!=)\s*(true|false|$Lval)\b(.*)$/i) {
+			my $lead = $1;
+			my $arg = $2;
+			my $test = $3;
+			my $otype = $4;
+			my $trail = $5;
+			my $op = "!";
+
+			($arg, $otype) = ($otype, $arg) if ($arg =~ /^(?:true|false)$/i);
+
+			my $type = lc($otype);
+			if ($type =~ /^(?:true|false)$/) {
+				if (("$test" eq "==" && "$type" eq "true") ||
+				    ("$test" eq "!=" && "$type" eq "false")) {
+					$op = "";
+				}
+
+				CHK("BOOL_COMPARISON",
+				    "Using comparison to $otype is error prone\n" . $herecurr);
+
+## maybe suggesting a correct construct would better
+##				    "Using comparison to $otype is error prone.  Perhaps use '${lead}${op}${arg}${trail}'\n" . $herecurr);
+
+			}
+		}
+
 # check for semaphores initialized locked
 		if ($line =~ /^.\s*sema_init.+,\W?0\W?\)/) {
 			WARN("CONSIDER_COMPLETION",