linux-kernel - Re: [PATCH 1/3] mm/gup: Use huge_ptep_get() in gup

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Date:   Thu, 18 Jun 2020 00:14:05 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Peter Zijlstra \(Intel\)" <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 1/3] mm/gup: Use huge_ptep_get() in gup_hugepte()

Christophe Leroy <christophe.leroy@...roup.eu> writes:
> gup_hugepte() reads hugepage table entries, it can't read
> them directly, huge_ptep_get() must be used.
>
> Fixes: 2ab3a0a02905 ("READ_ONCE: Enforce atomicity for {READ,WRITE}_ONCE() memory accesses")

I see that commit in older versions of linux-next but not in mainline.

In mainline it seems to be: 9e343b467c70 ("READ_ONCE: Enforce atomicity for {READ,WRITE}_ONCE() memory accesses")

I guess it got rebased somewhere along the way.

I fixed it up when applying, and the other two as well.

cheers

> Cc: Will Deacon <will@...nel.org>
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  mm/gup.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index de9e36262ccb..761df4944ef5 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2425,7 +2425,7 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
>  	if (pte_end < end)
>  		end = pte_end;
>  
> -	pte = READ_ONCE(*ptep);
> +	pte = huge_ptep_get(ptep);
>  
>  	if (!pte_access_permitted(pte, flags & FOLL_WRITE))
>  		return 0;
> -- 
> 2.25.0