Re: [PATCH] filemap: replace pte_offset_map() with pte_offset_map_nolock()

[David Hildenbrand]

On 13.03.24 02:29, Peng Zhang wrote:
> From: ZhangPeng <zhangpeng362@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Signed-off-by: ZhangPeng <zhangpeng362@xxxxxxxxxx>
> ---
>   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@xxxxxxxxxx>

--
Cheers,

David / dhildenb