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References: <20210716081449.22187-1-sj38.park@gmail.com>
 <20210716081449.22187-6-sj38.park@gmail.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Subject: Re: [PATCH v34 05/13] mm/damon: Implement primitives for the virtual
 memory address spaces
Message-ID: <358fa060-7702-d523-5169-f25a3de0c22e@redhat.com>
Date:   Thu, 26 Aug 2021 16:09:23 +0200
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> +static void damon_va_mkold(struct mm_struct *mm, unsigned long addr)
> +{
> +	pte_t *pte = NULL;
> +	pmd_t *pmd = NULL;
> +	spinlock_t *ptl;
> +

I just stumbled over this, sorry for the dumb questions:


a) What do we know about that region we are messing with?

AFAIU, just like follow_pte() and follow_pfn(), follow_invalidate_pte() 
should only be called on VM_IO and raw VM_PFNMAP mappings in general 
(see the doc of follow_pte()). Do you even know that it's within a 
single VMA and that there are no concurrent modifications?

b) Which locks are we holding?

I hope we're holding the mmap lock in read mode at least. Or how are you 
making sure there are no concurrent modifications to page tables / VMA 
layout ... ?

> +	if (follow_invalidate_pte(mm, addr, NULL, &pte, &pmd, &ptl))


-- 
Thanks,

David / dhildenb