linux-kernel - Re: [PATCH v2 02/18] perf/core: Replace READ_ONCE() with standard page table accessors

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Message-ID: <24beaa64-d144-42c3-945f-a37e1cac384d@arm.com>
Date: Thu, 9 Oct 2025 07:33:03 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Samuel Holland <samuel.holland@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>, Paul Walmsley <pjw@...nel.org>,
 linux-riscv@...ts.infradead.org
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, Conor Dooley <conor@...nel.org>,
 Alexandre Ghiti <alex@...ti.fr>, Emil Renner Berthing <kernel@...il.dk>,
 Andrew Morton <akpm@...ux-foundation.org>, Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>
Subject: Re: [PATCH v2 02/18] perf/core: Replace READ_ONCE() with standard
 page table accessors



On 09/10/25 7:27 AM, Samuel Holland wrote:
> Replace READ_ONCE() with standard page table accessors, i.e. pXXp_get(),
> which have a default implementation of READ_ONCE() if the architecture
> does not override them.
> 
> Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
> ---
> 
> Changes in v2:
>  - New patch for v2
> 
>  kernel/events/core.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 820127536e62b..952ba4e3d8815 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -8110,7 +8110,7 @@ static u64 perf_get_pgtable_size(struct mm_struct *mm, unsigned long addr)
>  	pte_t *ptep, pte;
>  
>  	pgdp = pgd_offset(mm, addr);
> -	pgd = READ_ONCE(*pgdp);
> +	pgd = pgdp_get(pgdp);
>  	if (pgd_none(pgd))
>  		return 0;
>  
> @@ -8118,7 +8118,7 @@ static u64 perf_get_pgtable_size(struct mm_struct *mm, unsigned long addr)
>  		return pgd_leaf_size(pgd);
>  
>  	p4dp = p4d_offset_lockless(pgdp, pgd, addr);
> -	p4d = READ_ONCE(*p4dp);
> +	p4d = p4dp_get(p4dp);
>  	if (!p4d_present(p4d))
>  		return 0;
>  
> @@ -8126,7 +8126,7 @@ static u64 perf_get_pgtable_size(struct mm_struct *mm, unsigned long addr)
>  		return p4d_leaf_size(p4d);
>  
>  	pudp = pud_offset_lockless(p4dp, p4d, addr);
> -	pud = READ_ONCE(*pudp);
> +	pud = pudp_get(pudp);
>  	if (!pud_present(pud))
>  		return 0;
>  

This is already under discussion here.

https://lore.kernel.org/all/20251006042622.1743675-1-anshuman.khandual@arm.com/