linux-kernel - Re: [PATCH] filemap: replace pte_offset_map() with pte_offset_map

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Date: Wed, 13 Mar 2024 10:22:27 +0100
From: David Hildenbrand <david@...hat.com>
To: Peng Zhang <zhangpeng362@...wei.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Cc: akpm@...ux-foundation.org, willy@...radead.org, ying.huang@...el.com,
 fengwei.yin@...el.com, aneesh.kumar@...ux.ibm.com, shy828301@...il.com,
 hughd@...gle.com, wangkefeng.wang@...wei.com, sunnanyong@...wei.com
Subject: Re: [PATCH] filemap: replace pte_offset_map() with
 pte_offset_map_nolock()

On 13.03.24 02:29, Peng Zhang wrote:
> From: ZhangPeng <zhangpeng362@...wei.com>
> 
> The vmf->ptl in filemap_fault_recheck_pte_none() is still set from
> handle_pte_fault(). But at the same time, we did a pte_unmap(vmf->pte).
> After a pte_unmap(vmf->pte) unmap and rcu_read_unlock(), the page table
> may be racily changed and vmf->ptl maybe fails to protect the actual
> page table.
> Fix this by replacing pte_offset_map() with pte_offset_map_nolock().
> 
> Fixes: 58f327f2ce80 ("filemap: avoid unnecessary major faults in filemap_fault()")
> Suggested-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: ZhangPeng <zhangpeng362@...wei.com>
> ---
>   mm/filemap.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 31ab455c4537..222adac7c9c5 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -3207,7 +3207,8 @@ static vm_fault_t filemap_fault_recheck_pte_none(struct vm_fault *vmf)
>   	if (!(vmf->flags & FAULT_FLAG_ORIG_PTE_VALID))
>   		return 0;
>   
> -	ptep = pte_offset_map(vmf->pmd, vmf->address);
> +	ptep = pte_offset_map_nolock(vma->vm_mm, vmf->pmd, vmf->address,
> +				     &vmf->ptl);
>   	if (unlikely(!ptep))
>   		return VM_FAULT_NOPAGE;
>   

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb