checkpatch: attempt to find unnecessary 'out of memory' messages

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>
Acked-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 17 insertions, 0 deletions

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 182be0f12407..ac1d6b0a6f09 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -4014,6 +4014,23 @@ 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;