Subject: Re: [PATCH 01/23] arm: allow pte_offset_map[_lock]() to fail

From: Matthew Wilcox <[email-masked]>
Date: Wed, 10 May 2023 15:28:13 +0100

On Tue, May 09, 2023 at 09:42:44PM -0700, Hugh Dickins wrote:
> diff --git a/arch/arm/lib/uaccess_with_memcpy.c b/arch/arm/lib/uaccess_with_memcpy.c
> index e4c2677cc1e9..2f6163f05e93 100644
> --- a/arch/arm/lib/uaccess_with_memcpy.c
> +++ b/arch/arm/lib/uaccess_with_memcpy.c
> @@ -74,6 +74,9 @@ pin_page_for_write(const void __user *_addr, pte_t **ptep, spinlock_t **ptlp)
>  		return 0;
>  
>  	pte = pte_offset_map_lock(current->mm, pmd, addr, &ptl);
> +	if (unlikely(!pte))
> +		return 0;

Failing seems like the wrong thig to do if we transitioned from a PTE
to PMD here?  Looks to me like we should goto a new label right after
the 'pmd = pmd_offset(pud, addr);', no?