[RFC PATCH] checkpatch: Attempt to find unnecessary 'out of memory' messages

[Joe Perches <joe@perches.com>]

Logging messages that show some type of "out of memory" error
are generally unnecessary as there is a generic message and
a stack dump done by the memory subsystem.

These messages generally increase kernel size without much
added value.

Emit a warning on these types of messages.

This test looks for any inserted message function, then looks
at the previous line for an "if (!foo)" or "if (foo == NULL)"
test and then looks at the preceding statement for an allocation
function like "foo = kmalloc()"

ie: this code matches:

	foo = kmalloc();
	if (foo == NULL) {
		printk("Out of memory\n");
		return -ENOMEM;
	}

This test is very crude and incomplete.

This test can miss quite a lot of of OOM messages that do not
have this specific form.

ie: this code does not match:

	foo = kmalloc();
	if (!foo) {
		rtn = -ENOMEM;
		printk("Out of memory!\n");
		goto out;
	}

This test could also be a false positive when the logging
message itself does not specify anything about memory, but
I did not find any false positives in my limited testing.

spatch could be a better solution but correctness seems
non-trivial for that tool too.

Signed-off-by: Joe Perches <joe@perches.com>
---
 scripts/checkpatch.pl | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 010b18e..64bee42 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -4009,6 +4009,23 @@ sub process {
 			}
 		}
 
+# check for unnecessary "Out of Memory" messages
+		if ($line =~ /^\+.*\b$logFunctions\s*\(/ &&
+		    $prevline =~ /^[ \+]\s*if\s*\(\s*(\!\s*|NULL\s*==\s*)?($Lval)(\s*==\s*NULL\s*)?\s*\)/ &&
+		    (defined $1 || defined $3) &&
+		    $linenr > 3) {
+			my $testval = $2;
+			my $testline = $lines[$linenr - 3];
+
+			my ($s, $c) = ctx_statement_block($linenr - 3, $realcnt, 0);
+#			print("line: <$line>\nprevline: <$prevline>\ns: <$s>\nc: <$c>\n\n\n");
+
+			if ($c =~ /(?:^|\n)[ \+]\s*(?:$Type\s*)?\Q$testval\E\s*=\s*(?:\([^\)]*\)\s*)?\s*(?:devm_)?(?:[kv][czm]alloc(?:_node|_array)?\b|kstrdup|(?:dev_)?alloc_skb)/) {
+				WARN("OOM_MESSAGE",
+				     "Possible unnecessary 'out of memory' message\n" . $hereprev);
+			}
+		}
+
 # check for bad placement of section $InitAttribute (e.g.: __initdata)
 		if ($line =~ /(\b$InitAttribute\b)/) {
 			my $attr = $1;