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

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Message-ID: <Z+nKOYxiTWGNI9FQ@MiWiFi-R3L-srv>
Date: Mon, 31 Mar 2025 06:48:25 +0800
From: Baoquan He <bhe@...hat.com>
To: Zhu Yanjun <yanjun.zhu@...ux.dev>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] mm/gup: fix wrongly calculated returned value in
 fault_in_safe_writeable()

On 03/30/25 at 09:43pm, Zhu Yanjun wrote:
> 在 2025/3/30 14:17, Baoquan He 写道:
> > Not like fault_in_writeable() or fault_in_writeable(), in
>                                    fault_in_readable()?
> 
> In the above, one of the 2 fault_in_writeable should be fault_in_readable()
> ?

You are right, I will fix it in v2. Thanks.

> > fault_in_safe_writeable() local variable 'start' is increased page
> > by page to loop till the whole address range is handled. However,
> > it mistakenly calcalates the size of handled range with 'uaddr - start'.
> > 
> > Fix it here.
> > 
> > Signed-off-by: Baoquan He <bhe@...hat.com>
> > ---
> >   mm/gup.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/mm/gup.c b/mm/gup.c
> > index 855ab860f88b..73777b1de679 100644
> > --- 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);
> 
>