linux-kernel - Re: [PATCH v2 1/7] mm/gup: fix wrongly calculated returned value in fault_in_safe

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Message-ID: <Z+v0VTq0YD3+9bMB@MiWiFi-R3L-srv>
Date: Tue, 1 Apr 2025 22:12:37 +0800
From: Baoquan He <bhe@...hat.com>
To: Oscar Salvador <osalvador@...e.de>
Cc: David Hildenbrand <david@...hat.com>, akpm@...ux-foundation.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	yanjun.zhu@...ux.dev
Subject: Re: [PATCH v2 1/7] mm/gup: fix wrongly calculated returned value in
 fault_in_safe_writeable()

On 04/01/25 at 04:00pm, Oscar Salvador wrote:
> On Tue, Apr 01, 2025 at 10:10:03AM +0200, David Hildenbrand wrote:
> > On 31.03.25 10:13, Baoquan He wrote:
> > > --- a/mm/gup.c
> > > +++ b/mm/gup.c
> > > @@ -2207,8 +2207,8 @@ size_t fault_in_safe_writeable(const char __user *uaddr, size_t size)
> > >   	} while (start != end);
> > >   	mmap_read_unlock(mm);
> > > -	if (size > (unsigned long)uaddr - start)
> > > -		return size - ((unsigned long)uaddr - start);
> > > +	if (size > start - (unsigned long)uaddr)
> > > +		return size - (start - (unsigned long)uaddr);
> > >   	return 0;
> > >   }
> > >   EXPORT_SYMBOL(fault_in_safe_writeable);
> > 
> > Can we instead just use the uaddr and start variables like in
> > fault_in_readable?
> > 
> > That is, turn "start" into a const and adjust uaddr instead.
> 
> Yes, I think that would be much cleaner.
> 
> Otherwise, this looks good to me. 

Will change in v3 as both of you suggested, thanks for reviewing this v2
series.