linux-kernel - Re: [iio:togreg 3/3] WARNING: Reusing the krealloc arg is almost always a bug

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Date:	Sun, 02 Mar 2014 04:06:45 -0800
From:	Joe Perches <joe@...ches.com>
To:	Lars-Peter Clausen <lars@...afoo.de>,
	Andy Whitcroft <apw@...dowen.org>
Cc:	Fengguang Wu <fengguang.wu@...el.com>,
	Jonathan Cameron <jic23@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [iio:togreg 3/3] WARNING: Reusing the krealloc arg is almost
 always a bug

(Adding Andy Whitcroft to cc's)

On Sun, 2014-03-02 at 10:11 +0100, Lars-Peter Clausen wrote:
> On 03/02/2014 03:24 AM, Fengguang Wu wrote:
> >
> > Hi Lars-Peter,
> >
> > FYI, there are new warnings show up in
> >
> > tree:   git://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git togreg
> > head:   bdc8cda1d010887c06bd8c29564b74cd61ec0a7b
> > commit: bdc8cda1d010887c06bd8c29564b74cd61ec0a7b [3/3] iio:adc: Add Xilinx XADC driver
> >
> > scripts/checkpatch.pl 0001-iio-adc-Add-Xilinx-XADC-driver.patch
> > # many are suggestions rather than must-fix
> > WARNING: Reusing the krealloc arg is almost always a bug
> > #1220: drivers/iio/adc/xilinx-xadc-core.c:1138:
> > +	indio_dev->channels = krealloc(channels, sizeof(*channels) *
> >
> 
> This is actually a false positive, checkpatch thinks that 
> 'indio_dev->channels' and 'channels' is the same. Added Joe to Cc.

Yeah.  perl finds an $Lval match for either
foo->bar and bar for

	foo->bar = krealloc(bar, 1, GFP_KERNEL);
	bar = krealloc(bar, 1, GFP_KERNEL);

I can't think of a "pretty" perl way to fix this
because I'm not much of a perl guy, but maybe this
patch below works well enough.

Find all the lvals when there's a possible krealloc
reuse.  Check the lvals before and after the krealloc.
Bleat if they not equal.

Andy?  Got any better idea?

---
 scripts/checkpatch.pl | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 91308be..7391e01 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -4275,9 +4275,15 @@ sub process {
 
 # check for krealloc arg reuse
 		if ($^V && $^V ge 5.10.0 &&
-		    $line =~ /\b($Lval)\s*\=\s*(?:$balanced_parens)?\s*krealloc\s*\(\s*\1\s*,/) {
-			WARN("KREALLOC_ARG_REUSE",
-			     "Reusing the krealloc arg is almost always a bug\n" . $herecurr);
+		    $line =~ /($Lval)\s*\=\s*(?:$balanced_parens)?\s*krealloc\s*\(\s*\1\s*,/) {
+			my @line_lvals = $line =~ m/$Lval/g;
+			for my $index (1 .. $#line_lvals - 1) {
+				if ($line_lvals[$index] eq "krealloc" &&
+				    $line_lvals[$index - 1] eq $line_lvals[$index + 1]) {
+					WARN("KREALLOC_ARG_REUSE",
+					     "Reusing the krealloc arg is almost always a bug\n" . $herecurr);
+				}
+			}
 		}
 
 # check for alloc argument mismatch


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