linux-kernel - Re: [PATCH] mm/debug_vm_pgtable: Fix build failure with powerpc 8xx

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Date:   Fri, 19 Jun 2020 16:45:39 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        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] mm/debug_vm_pgtable: Fix build failure with powerpc 8xx


On 06/18/2020 08:01 PM, Christophe Leroy wrote:
> Fix it by using the recently added ptep_get() helper.
> 
> Fixes: 9e343b467c70 ("READ_ONCE: Enforce atomicity for {READ,WRITE}_ONCE() memory accesses")
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  mm/debug_vm_pgtable.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index e45623016aea..61ab16fb2e36 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -246,13 +246,13 @@ static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
>  static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
>  				   unsigned long vaddr)
>  {
> -	pte_t pte = READ_ONCE(*ptep);
> +	pte_t pte = ptep_get(ptep);
>  
>  	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
>  	set_pte_at(mm, vaddr, ptep, pte);
>  	barrier();
>  	pte_clear(mm, vaddr, ptep);
> -	pte = READ_ONCE(*ptep);
> +	pte = ptep_get(ptep);
>  	WARN_ON(!pte_none(pte));
>  }

Tested this on arm64 and x86 platforms after applying the previous
series which adds ptep_get() and a follow up patch.

https://patchwork.kernel.org/project/linux-mm/list/?series=302949
https://patchwork.kernel.org/patch/11611929/

Build tested on s390 and arc platforms as well.

Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>