linux-kernel - Re: [PATCH] mm/dirty: Replace READ_ONCE() with pudp

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Message-ID: <1c948262-e201-4473-b156-8b90fedc9ce7@arm.com>
Date: Mon, 6 Oct 2025 11:58:20 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Dev Jain <dev.jain@....com>, linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/dirty: Replace READ_ONCE() with pudp_get()



On 06/10/25 11:37 AM, Dev Jain wrote:
> 
> On 06/10/25 11:22 am, Anshuman Khandual wrote:
>> Replace READ_ONCE() with a standard page table accessor i.e pudp_get() that
>> anyways defaults into READ_ONCE() in cases where platform does not override
>>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: David Hildenbrand <david@...hat.com>
>> Cc: linux-mm@...ck.org
>> Cc: linux-kernel@...r.kernel.org
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>> ---
>>   mm/mapping_dirty_helpers.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/mapping_dirty_helpers.c b/mm/mapping_dirty_helpers.c
>> index c193de6cb23a..737c407f4081 100644
>> --- a/mm/mapping_dirty_helpers.c
>> +++ b/mm/mapping_dirty_helpers.c
>> @@ -149,7 +149,7 @@ static int wp_clean_pud_entry(pud_t *pud, unsigned long addr, unsigned long end,
>>                     struct mm_walk *walk)
>>   {
>>   #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
>> -    pud_t pudval = READ_ONCE(*pud);
>> +    pud_t pudval = pudp_get(pud);
>>         /* Do not split a huge pud */
>>       if (pud_trans_huge(pudval)) {
> 
> Talking about mm, why not also make changes for these READ_ONCE accesses
> in gup, hmm, memory, mprotect, sparse-vmemmap?
> 

Right, could replace all mm/ READ_ONCE() for pxdp pointers with the pgtable helpers
but that will create too much code churn in a single patch. Thought of doing these
replacements per file will be much more contained which is easy both for review and
testing.