Date:   Wed, 16 Mar 2022 15:25:11 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Naoya Horiguchi <naoya.horiguchi@...ux.dev>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Yang Shi <shy828301@...il.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        <linux-kernel@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH v3] mm/hwpoison: set PageHWPoison after passing prechecks
 in memory_failure_hugetlb()

On 2022/3/16 9:45, Naoya Horiguchi wrote:
> From: Naoya Horiguchi <naoya.horiguchi@....com>
> 
> There is a race condition between memory_failure_hugetlb() and hugetlb
> free/demotion, which causes setting PageHWPoison flag on the wrong page
> (which was a hugetlb when memory_failure() was called, but was removed
> or demoted when memory_failure_hugetlb() is called).  This results in
> killing wrong processes.  So set PageHWPoison flag after passing prechecks.
> 
> The actual user-visible effect might be obscure because even if
> memory_failure() works as expected, some random process could be killed.
> Even worse, the actual error is left unhandled, so no one prevents later
> access to it, which might lead to more serious results like consuming
> corrupted data.
> 
> This patch depends on Miaohe's patch titled "mm/memory-failure.c: fix
> race with changing page compound again".
> 
> Reported-by: Mike Kravetz <mike.kravetz@...cle.com>
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@....com>
> Cc: <stable@...r.kernel.org>

This patch looks good to me. Many thanks!

Reviewed-by: Miaohe Lin <linmiaohe@...wei.com>

> ---
> ChangeLog v2 -> v3:
> - rename the patch because page lock is not the primary factor to
>   solve the reported issue.
> - updated description in the same manner.
> - call page_handle_poison() instead of __page_handle_poison() for
>   free hugepage case.
> - reorder put_page and unlock_page (thanks to Miaohe Lin)
> 
> ChangeLog v1 -> v2:
> - pass subpage to get_hwpoison_huge_page() instead of head page.
> - call compound_head() in hugetlb_lock to avoid race with hugetlb
>   demotion/free.
> ---
>  mm/hugetlb.c        |  8 +++++---
>  mm/memory-failure.c | 43 +++++++++++++++++++++----------------------
>  2 files changed, 26 insertions(+), 25 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index f294db835f4b..345fed90842e 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6761,14 +6761,16 @@ bool isolate_huge_page(struct page *page, struct list_head *list)
>  
>  int get_hwpoison_huge_page(struct page *page, bool *hugetlb)
>  {
> +	struct page *head;
>  	int ret = 0;
>  
>  	*hugetlb = false;
>  	spin_lock_irq(&hugetlb_lock);
> -	if (PageHeadHuge(page)) {
> +	head = compound_head(page);
> +	if (PageHeadHuge(head)) {
>  		*hugetlb = true;
> -		if (HPageFreed(page) || HPageMigratable(page))
> -			ret = get_page_unless_zero(page);
> +		if (HPageFreed(head) || HPageMigratable(head))
> +			ret = get_page_unless_zero(head);
>  		else
>  			ret = -EBUSY;
>  	}
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index a9bfd04d2a3c..c66d75b45864 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1193,7 +1193,7 @@ static int __get_hwpoison_page(struct page *page, unsigned long flags)
>  	int ret = 0;
>  	bool hugetlb = false;
>  
> -	ret = get_hwpoison_huge_page(head, &hugetlb);
> +	ret = get_hwpoison_huge_page(page, &hugetlb);
>  	if (hugetlb)
>  		return ret;
>  
> @@ -1280,11 +1280,10 @@ static int get_any_page(struct page *p, unsigned long flags)
>  
>  static int __get_unpoison_page(struct page *page)
>  {
> -	struct page *head = compound_head(page);
>  	int ret = 0;
>  	bool hugetlb = false;
>  
> -	ret = get_hwpoison_huge_page(head, &hugetlb);
> +	ret = get_hwpoison_huge_page(page, &hugetlb);
>  	if (hugetlb)
>  		return ret;
>  
> @@ -1502,34 +1501,21 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
>  	struct page *head = compound_head(p);
>  	int res;
>  	unsigned long page_flags;
> -
> -	if (TestSetPageHWPoison(head)) {
> -		pr_err("Memory failure: %#lx: already hardware poisoned\n",
> -		       pfn);
> -		res = -EHWPOISON;
> -		if (flags & MF_ACTION_REQUIRED)
> -			res = kill_accessing_process(current, page_to_pfn(head), flags);
> -		return res;
> -	}
> -
> -	num_poisoned_pages_inc();
> +	bool put = false;
> +	bool already_hwpoisoned = false;
>  
>  	if (!(flags & MF_COUNT_INCREASED)) {
>  		res = get_hwpoison_page(p, flags);
>  		if (!res) {
>  			lock_page(head);
>  			if (hwpoison_filter(p)) {
> -				if (TestClearPageHWPoison(head))
> -					num_poisoned_pages_dec();
>  				unlock_page(head);
>  				return -EOPNOTSUPP;
>  			}
>  			unlock_page(head);
>  			res = MF_FAILED;
> -			if (__page_handle_poison(p)) {
> -				page_ref_inc(p);
> +			if (page_handle_poison(p, true, false))
>  				res = MF_RECOVERED;
> -			}
>  			action_result(pfn, MF_MSG_FREE_HUGE, res);
>  			return res == MF_RECOVERED ? 0 : -EBUSY;
>  		} else if (res < 0) {
> @@ -1553,13 +1539,18 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
>  	page_flags = head->flags;
>  
>  	if (hwpoison_filter(p)) {
> -		if (TestClearPageHWPoison(head))
> -			num_poisoned_pages_dec();
> -		put_page(p);
> +		put = true;
>  		res = -EOPNOTSUPP;
>  		goto out;
>  	}
>  
> +	if (TestSetPageHWPoison(head)) {
> +		put = already_hwpoisoned = true;
> +		goto out;
> +	}
> +
> +	num_poisoned_pages_inc();
> +
>  	/*
>  	 * TODO: hwpoison for pud-sized hugetlb doesn't work right now, so
>  	 * simply disable it. In order to make it work properly, we need
> @@ -1584,6 +1575,14 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
>  	return identify_page_state(pfn, p, page_flags);
>  out:
>  	unlock_page(head);
> +	if (put)
> +		put_page(p);
> +	if (already_hwpoisoned) {
> +		pr_err("Memory failure: %#lx: already hardware poisoned\n", pfn);
> +		res = -EHWPOISON;
> +		if (flags & MF_ACTION_REQUIRED)
> +			res = kill_accessing_process(current, page_to_pfn(head), flags);
> +	}
>  	return res;
>  }
>  
> 

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