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Date:   Sat, 15 Apr 2023 09:11:20 +0100
From:   Lorenzo Stoakes <lstoakes@gmail.com>
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/7] mm/gup: remove vmas parameter from
 get_user_pages_remote()
Message-ID: <e712589f-f4c0-4037-8a3c-0d48bd35baef@lucifer.local>
References: <cover.1681508038.git.lstoakes@gmail.com>
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 <e715ec72-682f-291c-7131-8355843660d0@I-love.SAKURA.ne.jp>
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On Sat, Apr 15, 2023 at 09:25:51AM +0900, Tetsuo Handa wrote:
> On 2023/04/15 8:27, Lorenzo Stoakes wrote:
> > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
> > index f5bcb0dc6267..74d8d4007dec 100644
> > --- a/arch/arm64/kernel/mte.c
> > +++ b/arch/arm64/kernel/mte.c
> > @@ -437,8 +437,9 @@ static int __access_remote_tags(struct mm_struct *mm, unsigned long addr,
> >  		struct page *page = NULL;
> >
> >  		ret = get_user_pages_remote(mm, addr, 1, gup_flags, &page,
> > -					    &vma, NULL);
> > -		if (ret <= 0)
> > +					    NULL);
> > +		vma = vma_lookup(mm, addr);
> > +		if (ret <= 0 || !vma)
> >  			break;
>
> This conversion looks wrong. When get_user_pages_remote(&page) returned > 0,
> put_page(page) is needed even if vma_lookup() returned NULL, isn't it?
>

You're right, though actually it's not possible for ret > 0 and vma != NULL
because the GUP code requires the VMA to exist for it to have returned > 0.

I was trying to be too cute here I think, actually we only want to be doing
that lookup if the GUP succeeded in any case.

Let me respin with a fix for this.