[PATCH v2] checkpatch: Add a warning for log messages that don't end in a new line

[Logan Gunthorpe]

Check for lines with a log function using a relatively strict regular
expression catching only printk, dev_* and pr_* functions. Once
one is found, accumulate further lines for any functions that
are split over multiple lines. Stop accumulating the log function line
when we find a ';' or match the full format string.

A get_log_fmt() function is used to find either the first or
second argument (depending on the log function matched) as the
format string. If the format argument ends in '\n"', then we conclude
that the logging call is correct. If the line ends in '%s"', then we
only print a CHK warning as the developer *may* have the newline in an
argument string. Otherwise we print a warning that the line is
likely missing a new line.

Because we are trying to match multiple lines, we must also match
lines that are part of the context of the patch. In order to ensure
we don't print a message on log lines that are only part of context,
we track that at least one line was added using the $log_func_changed
flag.

To handle continuations, during pre-processing we search for all
pr_cont and KERN_CONT instances and create a hash set of the line
numbers of all preceding log function calls. The hash set is then used
to mask out any calls that are likely followed by continuations. This
should handle many cases, however a small number of false positives are
likely going to occur in cases where a patch's context does not cover
the following KERN_CONT. This is acceptable, in my opinion, seeing
KERN_CONT is already discouraged and will create it's own warnings that
the developer has to reason about.

I've created a small test suite to test this change which can be found
on github[1]. I've also run this on the kernel source and found more
than 6000 violations. I reviewed a random sampling of these for false
positives and have not found any.

Thanks to Joe for describing how to properly test a change such as this.

[1] https://github.com/lsgunth/checkpatch-tests

Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Cc: Andy Whitcroft <apw@xxxxxxxxxxxxx>
Cc: Joe Perches <joe@xxxxxxxxxxx>
---

Here's my second attempt at this. As described in the commit log,
I've made it a bit more sophisticated and fixed a number of issues with
how the patch format is processed. The testing has also improved
significantly having run it on the entire kernel source as well as
a suite of test cases. The patch isn't entirely perfect (per the note
about false positives) but I feel it's close enough that its benefits
outweighs this. (As it only annoys developers who are working with a
discouraged feature.)

As mentioned in the commit log, I've found more than 6000 instances
that look like this error. I've seen a few cases that appear to have
intended to use KERN_CONT but didn't and are thus caught by this.
If there are any heroic kernel janitors that are interested in tackling
these issues, the list can be found here:

https://github.com/lsgunth/checkpatch-tests/blob/master/results/v4.14

 scripts/checkpatch.pl | 80 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 80 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 8b80bac055e4..cdd767af6566 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -460,6 +460,34 @@ our $logFunctions = qr{(?x:
 	seq_vprintf|seq_printf|seq_puts
 )};

+
+our $logNewLineFirstArg = qr{(?x:
+	printk(?:_ratelimited|_once|_deferred_once|_deferred|)|
+	pr_(?:printk|emerg|alert|crit|err|warning|warn|notice|info|debug|dbg|vdbg|devel|cont|WARN)(?:_ratelimited|_once|)
+)};
+
+our $logNewLineSecondArg = qr{(?x:
+	dev_(?:printk|emerg|alert|crit|err|warning|warn|notice|info|debug|dbg|vdbg|devel|WARN)(?:_ratelimited|_once|)
+)};
+
+our $logNewLineFunctions = qr{(?x:
+    $logNewLineFirstArg |
+    $logNewLineSecondArg
+)};
+
+sub get_log_fmt {
+	my ($line, $rawline) = @_;
+
+	if ($line =~ m/\b$logNewLineFirstArg\(([^,)]+)[,)]/g) {
+		return substr($rawline, $-[1], $+[1] - $-[1]);
+	} elsif($line =~ m/\b$logNewLineSecondArg\([^,]+,([^,)]+)[,)]/g) {
+		return substr($rawline, $-[1], $+[1] - $-[1]);
+	} else {
+		return "";
+	}
+}
+
+
 our $signature_tags = qr{(?xi:
 	Signed-off-by:|
 	Acked-by:|
@@ -2224,6 +2252,13 @@ sub process {

 	my $camelcase_file_seeded = 0;

+	my $in_log_function = 0;
+	my $log_func_changed = 0;
+	my $log_func_line = "";
+	my $log_func_rawline = "";
+	my $log_last_linenr = -1;
+	my %log_func_continued = ();
+
 	sanitise_line_reset();
 	my $line;
 	foreach my $rawline (@rawlines) {
@@ -2287,6 +2322,15 @@ sub process {
 			# simplify matching -- only bother with positive lines.
 			$line = sanitise_line($rawline);
 		}
+
+		if ($log_last_linenr > 0 && $line =~ /(KERN_CONT|pr_cont)/) {
+			$log_func_continued{$log_last_linenr} = ();
+		}
+
+		if ($line =~ /\b$logNewLineFunctions\(/) {
+			$log_last_linenr = $linenr;
+		}
+
 		push(@lines, $line);

 		if ($realcnt > 1) {
@@ -2321,6 +2365,7 @@ sub process {
 		    $line =~ /^\@\@ -\d+(?:,\d+)? \+(\d+)(,(\d+))? \@\@(.*)/) {
 			my $context = $4;
 			$is_patch = 1;
+			$in_log_function = 0;
 			$first_line = $linenr + 1;
 			$realline=$1-1;
 			if (defined $2) {
@@ -3505,6 +3550,41 @@ sub process {
 		}
 		$prev_values = substr($curr_values, -1);

+# check for logging functions with lines that don't end in a '\n"'
+		if ($line =~ /\b$logNewLineFunctions\(/ &&
+		    !exists $log_func_continued{$linenr}) {
+			$in_log_function = 1;
+			$log_func_changed = 0;
+			$log_func_rawline = "";
+			$log_func_line = "";
+		}
+		if ($in_log_function) {
+			if ($line =~ /^\+/)  {
+				$log_func_changed = 1;
+			}
+
+			$log_func_rawline .= $rawline;
+			$log_func_line .= $line;
+			my $fmt_string = get_log_fmt($log_func_line,
+						     $log_func_rawline);
+
+			if ($fmt_string && !$log_func_changed) {
+				$in_log_function = 0;
+			} elsif ($fmt_string =~ /\\n"$/) {
+				$in_log_function = 0;
+			} elsif ($fmt_string =~ /%s"$/) {
+				CHK("LOGGING_MISSING_NEWLINE",
+				    "Log message may not end in new line (\\n)\n" . $herecurr);
+				$in_log_function = 0;
+			} elsif ($fmt_string =~ /"$/) {
+				WARN("LOGGING_MISSING_NEWLINE",
+				     "Log messages should end in a line feed (\\n)\n" . $herecurr);
+				$in_log_function = 0;
+			} elsif ($line =~ /;$/) {
+				$in_log_function = 0;
+			}
+		}
+
 #ignore lines not being added
 		next if ($line =~ /^[^\+]/);

--
2.11.0