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Date:   Wed, 12 May 2021 04:15:17 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Kefeng Wang <wangkefeng.wang@huawei.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/3] mm/debug: Check page poisoned firstly in dump_page()
Message-ID: <YJtIRR2NfpRtYQrG@casper.infradead.org>
References: <20210512031057.13580-1-wangkefeng.wang@huawei.com>
 <20210512031057.13580-3-wangkefeng.wang@huawei.com>
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On Wed, May 12, 2021 at 11:10:57AM +0800, Kefeng Wang wrote:
> If page is poisoned, it will crash when we call some page related
> functions, so must check whether the page is poisoned or not firstly.

https://lore.kernel.org/linux-mm/20210430145549.2662354-4-willy@infradead.org/

> Fixes: 6197ab984b41 ("mm: improve dump_page() for compound pages")
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
>  mm/debug.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/debug.c b/mm/debug.c
> index 84cdcd0f7bd3..cf84cd9df527 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -44,20 +44,19 @@ const struct trace_print_flags vmaflag_names[] = {
>  
>  static void __dump_page(struct page *page, const char *reason)
>  {
> -	struct page *head = compound_head(page);
> +	struct page *head = NULL;
>  	struct address_space *mapping;
> -	bool page_poisoned = PagePoisoned(page);
> -	bool compound = PageCompound(page);
> +	bool compound;
>  	/*
>  	 * Accessing the pageblock without the zone lock. It could change to
>  	 * "isolate" again in the meantime, but since we are just dumping the
>  	 * state for debugging, it should be fine to accept a bit of
>  	 * inaccuracy here due to racing.
>  	 */
> -	bool page_cma = is_migrate_cma_page(page);
> +	bool page_cma;
>  	int mapcount;
>  	char *type = "";
> -
> +	bool page_poisoned = PagePoisoned(page);
>  	/*
>  	 * If struct page is poisoned don't access Page*() functions as that
>  	 * leads to recursive loop. Page*() check for poisoned pages, and calls
> @@ -68,6 +67,10 @@ static void __dump_page(struct page *page, const char *reason)
>  		goto hex_only;
>  	}
>  
> +	head = compound_head(page);
> +	page_poisoned = PagePoisoned(page);
> +	page_cma = is_migrate_cma_page(page);
> +
>  	if (page < head || (page >= head + MAX_ORDER_NR_PAGES)) {
>  		/*
>  		 * Corrupt page, so we cannot call page_mapping. Instead, do a
> @@ -178,7 +181,7 @@ static void __dump_page(struct page *page, const char *reason)
>  	print_hex_dump(KERN_WARNING, "raw: ", DUMP_PREFIX_NONE, 32,
>  			sizeof(unsigned long), page,
>  			sizeof(struct page), false);
> -	if (head != page)
> +	if (head && head != page)
>  		print_hex_dump(KERN_WARNING, "head: ", DUMP_PREFIX_NONE, 32,
>  			sizeof(unsigned long), head,
>  			sizeof(struct page), false);
> -- 
> 2.26.2
> 
>