linux-kernel - Re: [PATCH 04/12] selftests/mm: fix a char* assignment in mlock2-tests.c

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Date:   Mon, 5 Jun 2023 11:45:35 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Peter Xu <peterx@...hat.com>
CC:     David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>, <linux-mm@...ck.org>,
        <linux-kselftest@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/12] selftests/mm: fix a char* assignment in
 mlock2-tests.c

On 6/5/23 08:38, Peter Xu wrote:
...
>>>> I'm probably missing something, but what is the stop variable supposed to do
>>>> here? It's completely unused, no?
>>>>
>>>> if (!strchr(end_addr, ' ')) {
>>>> 	printf("cannot parse /proc/self/maps\n");
>>>> 	goto out;
>>>> }
>>
>> Yes it is! I certainly had tunnel vision on that one. I've changed the
>> patch to simply delete that line, for v2, thanks.
>>
>>>
>>> I guess it wanted to do "*stop = '\0'" but it just didn't matter a lot
>>> since the sscanf() just worked..
>>>
>>
>> Maybe, yes. Hard to tell the original intent at this point...it might
>> have been used in an early draft version of the loop that didn't get
>> posted, perhaps.
> 
> I'm pretty sure of it.. see the pattern:
> 
> 		end_addr = strchr(line, '-');
> 		if (!end_addr) {
> 			printf("cannot parse /proc/self/maps\n");
> 			goto out;
> 		}
> 		*end_addr = '\0';
> 
> And...
> 
> 		stop = strchr(end_addr, ' ');
> 		if (!stop) {
> 			printf("cannot parse /proc/self/maps\n");
> 			goto out;
> 		}
> 		stop = '\0';    <------------------- only diff here
> 

Yes, and that pattern shows why it wants to be "*stop = '\0';", but
it doesn't show why the author wasted a line of code in the first
place, setting a variable that is not used afterwards.

In other words, changing this to "*stop = '\0';" would make it
look pretty, but it's a non-functional line of code to add. Which
is why I think it should just be deleted at this point.

thanks,
-- 
John Hubbard
NVIDIA