linux-kernel - Re: [PATCH] checkpatch: Resolve improper warning for krealloc arg reuse

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Date:   Wed, 18 Jul 2018 10:46:58 -0700
From:   Joe Perches <joe@...ches.com>
To:     Manish Narani <manish.narani@...inx.com>, apw@...onical.com,
        linux-kernel@...r.kernel.org
Cc:     anirudh@...inx.com, sgoud@...inx.com, svemula@...inx.com
Subject: Re: [PATCH] checkpatch: Resolve improper warning for krealloc arg
 reuse

On Wed, 2018-07-18 at 19:25 +0530, Manish Narani wrote:
> Correct the check for reuse of krealloc. It gives false warning when a
> structure member variable name and krealloc argument name is same.
> 
> For Example:
> {
> 	...
> 	abc.def_var = krealloc(def_var, sizeof(*def_var),
> 				    GFP_KERNEL);
> 	...
> }
> 
> $ ./scripts/checkpatch.pl -f file.c
> 
> WARNING: Reusing the krealloc arg is almost always a bug
> +	abc.def_var = krealloc(def_var, sizeof(*def_var),
> 
> This patch resolves the above false warning.
> 
> Signed-off-by: Manish Narani <manish.narani@...inx.com>
> ---
>  scripts/checkpatch.pl | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 447857f..db9b666 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -6119,7 +6119,7 @@ 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*,/) {
> +		    $line =~ /\b($Lval)\s*\=\s*(?:$balanced_parens)?\s*krealloc\s*\(\s*\1\s*,/ && $line !~ m/[\.|\-\>].*\s*\=\s*.*/) {
>  			WARN("KREALLOC_ARG_REUSE",
>  			     "Reusing the krealloc arg is almost always a bug\n" . $herecurr);
>  		}

This works, though I'm not completely sure why.

Andy or anyone else:  Does your perl-foo understand why?

$ cat test_krealloc.c
static int xadc_parse_dt(struct iio_dev *indio_dev, struct device_node *np,
	unsigned int *conf)
{
	indio_dev->channels = krealloc(channels, sizeof(*channels) *
					num_channels, GFP_KERNEL);
	indio_dev->channels = krealloc(indio_dev->channels, sizeof(*channels) *
					num_channels, GFP_KERNEL);
}

For the patch below, the old case matches the first
$Lval above as "channels" skipping the "indio_dev->"
bit and as not "indio_dev->channels"

The modified patch below matches the first $Lval as the
expected "indio_dev->channels"
---
 scripts/checkpatch.pl | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index ed4fa986e8da..59eaaede757a 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -6149,7 +6149,8 @@ sub process {
 
 # check for krealloc arg reuse
 		if ($perl_version_ok &&
-		    $line =~ /\b($Lval)\s*\=\s*(?:$balanced_parens)?\s*krealloc\s*\(\s*\1\s*,/) {
+		    $line =~ /\b($Lval)\s*\=\s*(?:$balanced_parens)?\s*krealloc\s*\(\s*($Lval)\s*,/ &&
+		    $1 eq $3) {
 			WARN("KREALLOC_ARG_REUSE",
 			     "Reusing the krealloc arg is almost always a bug\n" . $herecurr);
 		}