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

walter harms
2015-02-03T08:48:01Z

Am 02.02.2015 20:46, schrieb NeilBrown:
> On Mon, 02 Feb 2015 16:20:42 +0100 SF Markus Elfring
> <elfring@users.sourceforge.net> wrote:
>
>> From: Markus Elfring <elfring@users.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@users.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.
>

hello Neil,
just for my curiosity.
is it possible that a bp[k] exists but bp[k].hijacked is 0 ?
if that case: kfree(bp) would free an object in use.
otherwise hijacked seems useless here as it is possible to free
everything.

re,
wh