linux-kernel - Re: [PATCH 2/3] md/bitmap: Delete an unnecessary check before the function call "kfree"

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Date:	Tue, 3 Feb 2015 06:46:03 +1100
From:	NeilBrown <neilb@...e.de>
To:	SF Markus Elfring <elfring@...rs.sourceforge.net>
Cc:	linux-raid@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	kernel-janitors@...r.kernel.org,
	Julia Lawall <julia.lawall@...6.fr>
Subject: Re: [PATCH 2/3] md/bitmap: Delete an unnecessary check before the
 function call "kfree"

On Mon, 02 Feb 2015 16:20:42 +0100 SF Markus Elfring
<elfring@...rs.sourceforge.net> wrote:

> From: Markus Elfring <elfring@...rs.sourceforge.net>
> Date: Mon, 2 Feb 2015 15:10:57 +0100
> 
> The kfree() function tests whether its argument is NULL and then
> returns immediately. Thus the test around the call is not needed.
> 
> * This issue was detected by using the Coccinelle software.
> 
> * Let us also move an assignment for the variable "pages" to the place
>   directly before it is really needed for a loop.
> 
> * Let us also move another kfree() call into a block which should belong
>   to a previous check for the variable "bp".
> 
> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> ---
>  drivers/md/bitmap.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
> index da3604e..47d72df 100644
> --- a/drivers/md/bitmap.c
> +++ b/drivers/md/bitmap.c
> @@ -1586,15 +1586,15 @@ static void bitmap_free(struct bitmap *bitmap)
>  	bitmap_file_unmap(&bitmap->storage);
>  
>  	bp = bitmap->counts.bp;
> -	pages = bitmap->counts.pages;
>  
>  	/* free all allocated memory */
> -
> -	if (bp) /* deallocate the page memory */
> +	if (bp) { /* deallocate the page memory */
> +		pages = bitmap->counts.pages;
>  		for (k = 0; k < pages; k++)
> -			if (bp[k].map && !bp[k].hijacked)
> +			if (!bp[k].hijacked)
>  				kfree(bp[k].map);
> -	kfree(bp);
> +		kfree(bp);
> +	}
>  	kfree(bitmap);
>  }
>  

Hi,
 I'm somewhat amused that you removed a test for one kfree, but imposed a
 test on another.  I realised the second test was already there, but why not
 just:

diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index da3604e73e8a..ad13b2e1bf1f 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -1592,7 +1592,7 @@ static void bitmap_free(struct bitmap *bitmap)
 
 	if (bp) /* deallocate the page memory */
 		for (k = 0; k < pages; k++)
-			if (bp[k].map && !bp[k].hijacked)
+			if (!bp[k].hijacked)
 				kfree(bp[k].map);
 	kfree(bp);
 	kfree(bitmap);


It makes the intention of the patch much clearer.

I'd probably prefer to leave the code as it is.  I don't think either patch
is really an improvement in readability, and readability trumps performance
in places like this.

Thanks,
NeilBrown

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