linux-kernel - Re: [PATCH] mm/huge_memory: Return from zap_huge_pmd after WARN

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Date:   Fri, 15 Jul 2022 18:50:36 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Zhou Guanghui <zhouguanghui1@...wei.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH] mm/huge_memory: Return from zap_huge_pmd after WARN_ONCE.

On Fri, Jul 15, 2022 at 09:22:38AM +0000, Zhou Guanghui wrote:
> After WARN_ONCE is processed, the subsequent page judgment results
> in NULL pointer access. It is more reasonable to return from the
> function here.

I'm not sure this is a good idea.  Probably better to crash than
continue.

> Signed-off-by: Zhou Guanghui <zhouguanghui1@...wei.com>
> ---
>  mm/huge_memory.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 834f288b3769..7f5ccca6792a 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1601,8 +1601,11 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>  			entry = pmd_to_swp_entry(orig_pmd);
>  			page = pfn_swap_entry_to_page(entry);
>  			flush_needed = 0;
> -		} else
> +		} else {
> +			spin_unlock(ptl);
>  			WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
> +			return 1;
> +		}
>  
>  		if (PageAnon(page)) {
>  			zap_deposited_table(tlb->mm, pmd);
> -- 
> 2.17.1
> 
>