Re: [PATCH 3/3] mm/memory-failure: send SIGBUS in the event of thp split fail

[Miaohe Lin <linmiaohe@huawei.com>]

On 2024/5/2 7:24, Jane Chu wrote:
> When handle hwpoison in a GUP longterm pin'ed thp page,
> try_to_split_thp_page() will fail. And at this point, there is little else
> the kernel could do except sending a SIGBUS to the user process, thus
> give it a chance to recover.
> 
> Signed-off-by: Jane Chu <jane.chu@oracle.com>

Thanks for your patch. Some comments below.

> ---
>  mm/memory-failure.c | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 7fcf182abb96..67f4d24a98e7 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -2168,6 +2168,37 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
>  	return rc;
>  }
>  
> +/*
> + * The calling condition is as such: thp split failed, page might have
> + * been GUP longterm pinned, not much can be done for recovery.
> + * But a SIGBUS should be delivered with vaddr provided so that the user
> + * application has a chance to recover. Also, application processes'
> + * election for MCE early killed will be honored.
> + */
> +static int kill_procs_now(struct page *p, unsigned long pfn, int flags,
> +			struct page *hpage)
> +{
> +	struct folio *folio = page_folio(hpage);
> +	LIST_HEAD(tokill);
> +	int res = -EHWPOISON;
> +
> +	/* deal with user pages only */
> +	if (PageReserved(p) || PageSlab(p) || PageTable(p) || PageOffline(p))
> +		res = -EBUSY;
> +	if (!(PageLRU(hpage) || PageHuge(p)))
> +		res = -EBUSY;

Above checks seems unneeded. We already know it's thp?

> +
> +	if (res == -EHWPOISON) {
> +		collect_procs(folio, p, &tokill, flags & MF_ACTION_REQUIRED);
> +		kill_procs(&tokill, true, pfn, flags);
> +	}
> +
> +	if (flags & MF_COUNT_INCREASED)
> +		put_page(p);

This if block is broken. put_page() has been done when try_to_split_thp_page() fails?

> +

action_result is missing?

> +	return res;
> +}
> +
>  /**
>   * memory_failure - Handle memory failure of a page.
>   * @pfn: Page Number of the corrupted page
> @@ -2297,6 +2328,11 @@ int memory_failure(unsigned long pfn, int flags)
>  		 */
>  		SetPageHasHWPoisoned(hpage);
>  		if (try_to_split_thp_page(p) < 0) {

Should hwpoison_filter() be called in this case?

> +			if (flags & MF_ACTION_REQUIRED) {
> +				pr_err("%#lx: thp split failed\n", pfn);
> +				res = kill_procs_now(p, pfn, flags, hpage);

Can we use hwpoison_user_mappings() directly here?

Thanks.
.

> +				goto unlock_mutex;
> +			}
>  			res = action_result(pfn, MF_MSG_UNSPLIT_THP, MF_IGNORED);
>  			goto unlock_mutex;
>  		}
>