linux-kernel - Re: [PATCH v4 4/4] mm/gup: clean up codes in fault_in

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Message-ID: <b5d0d34d-8aed-48a3-a484-8a60481860cb@redhat.com>
Date: Sun, 13 Apr 2025 22:02:55 +0200
From: David Hildenbrand <david@...hat.com>
To: Baoquan He <bhe@...hat.com>
Cc: linux-mm@...ck.org, akpm@...ux-foundation.org, osalvador@...e.de,
 yanjun.zhu@...ux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 4/4] mm/gup: clean up codes in fault_in_xxx() functions

On 13.04.25 03:07, Baoquan He wrote:
> On 04/11/25 at 01:41pm, David Hildenbrand wrote:
>> On 11.04.25 13:15, Baoquan He wrote:
>>> On 04/11/25 at 10:54am, David Hildenbrand wrote:
>>>> On 10.04.25 05:57, Baoquan He wrote:
>>>>> The code style in fault_in_readable() and fault_in_writable() is a
>>>>> little inconsistent with fault_in_safe_writeable(). In fault_in_readable()
>>>>> and fault_in_writable(), it uses 'uaddr' passed in as loop cursor. While
>>>>> in fault_in_safe_writeable(), local variable 'start' is used as loop
>>>>> cursor. This may mislead people when reading code or making change in
>>>>> these codes.
>>>>>
>>>>> Here define explicit loop cursor and use for loop to simplify codes in
>>>>> these three functions. These cleanup can make them be consistent in
>>>>> code style and improve readability.
>>>>>
>>>>> Signed-off-by: Baoquan He <bhe@...hat.com>
>>>>> ---
>>>>>     mm/gup.c | 65 +++++++++++++++++++++++---------------------------------
>>>>>     1 file changed, 26 insertions(+), 39 deletions(-)
>>>>>
>>>>> diff --git a/mm/gup.c b/mm/gup.c
>>>>> index 77a5bc622567..a76bd7e90a71 100644
>>>>> --- a/mm/gup.c
>>>>> +++ b/mm/gup.c
>>>>> @@ -2113,28 +2113,24 @@ static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start,
>>>>>      */
>>>>>     size_t fault_in_writeable(char __user *uaddr, size_t size)
>>>>>     {
>>>>> -	char __user *start = uaddr, *end;
>>>>> +	const unsigned long start = (unsigned long)uaddr;
>>>>> +	const unsigned long end = start + size;
>>>>> +	unsigned long cur = start;
>>>>
>>>> I would initialize cur in the for loop header, makes the loop easier to
>>>> read.
>>>
>>> Both is fine to me. It's to satisfy checkpatch.sh which complains about
>>> exceeding 80 char in the line.
>>
>> Did checkpatch.sh actually complain? You might be happy to learn that the
>> new limit is 100. :)
> 
> That's great to know. I never noticed this and always wrap via vim's
> indication.

Note that coding style says:

"
The preferred limit on the length of a single line is 80 columns.

Statements longer than 80 columns should be broken into sensible chunks,
unless exceeding 80 columns significantly increases readability and does
not hide information.
"

So 80 is still recommended, but there is nothing wrong about exceeding 
80 if there is good reason.


-- 
Cheers,

David / dhildenb