linux-kernel - Re: [PATCH v3 5/5] mm/memory-failure: send SIGBUS in the event of thp split fail

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Date: Thu, 23 May 2024 11:02:38 +0800
From: Miaohe Lin <linmiaohe@...wei.com>
To: Jane Chu <jane.chu@...cle.com>, <nao.horiguchi@...il.com>,
	<akpm@...ux-foundation.org>, <osalvador@...e.de>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 5/5] mm/memory-failure: send SIGBUS in the event of thp
 split fail

On 2024/5/22 7:54, Jane Chu wrote:
> While handling hwpoison in a THP page, it is possible that
> try_to_split_thp_page() fails. For example, when the THP page has
> been RDMA pinned. At this point, the kernel cannot isolate the
> poisoned THP page, all it could do is to send a SIGBUS to the user
> process with meaningful payload to give user-level recovery a chance.
> 

Thanks for your patch.

> Signed-off-by: Jane Chu <jane.chu@...cle.com>
> ---
>  mm/memory-failure.c | 35 ++++++++++++++++++++++++++++++-----
>  1 file changed, 30 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 794196951a04..a14d56e66902 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1706,7 +1706,12 @@ static int identify_page_state(unsigned long pfn, struct page *p,
>  	return page_action(ps, p, pfn);
>  }
>  
> -static int try_to_split_thp_page(struct page *page)
> +/*
> + * When 'release' is 'false', it means that if thp split has failed,
> + * there is still more to do, hence the page refcount we took earlier
> + * is still needed.
> + */
> +static int try_to_split_thp_page(struct page *page, bool release)
>  {
>  	int ret;
>  
> @@ -1714,7 +1719,7 @@ static int try_to_split_thp_page(struct page *page)
>  	ret = split_huge_page(page);
>  	unlock_page(page);
>  
> -	if (unlikely(ret))
> +	if (ret && release)
>  		put_page(page);

Is "unlikely" still needed?

>  
>  	return ret;
> @@ -2187,6 +2192,24 @@ 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 RDMA 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 folio *folio)
> +{
> +	LIST_HEAD(tokill);
> +
> +	collect_procs(folio, p, &tokill, flags & MF_ACTION_REQUIRED);
> +	kill_procs(&tokill, true, pfn, flags);
> +
> +	return -EHWPOISON;
> +}
> +
>  /**
>   * memory_failure - Handle memory failure of a page.
>   * @pfn: Page Number of the corrupted page
> @@ -2328,8 +2351,10 @@ int memory_failure(unsigned long pfn, int flags)
>  		 * page is a valid handlable page.
>  		 */
>  		folio_set_has_hwpoisoned(folio);
> -		if (try_to_split_thp_page(p) < 0) {
> -			res = action_result(pfn, MF_MSG_UNSPLIT_THP, MF_IGNORED);
> +		if (try_to_split_thp_page(p, false) < 0) {
> +			res = kill_procs_now(p, pfn, flags, folio);

No strong opinion but we might remove the return value of kill_procs_now as
it always return -EHWPOISON? We could simply set res to -EHWPOISON here.

Besides from above possible nits, this patch looks good to me.
Acked-by: Miaohe Lin <linmiaohe@...wei.com>
Thanks.
.