linux-kernel - Re: [PATCH 3/3] mm/debug: Check page poisoned firstly in dump

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Date:   Wed, 12 May 2021 11:23:24 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] mm/debug: Check page poisoned firstly in dump_page()



On 2021/5/12 11:15, Matthew Wilcox wrote:
> 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/

OK, please ignore them, I found this when debug arm issue in lts5.10, 
thanks.

> 
>> Fixes: 6197ab984b41 ("mm: improve dump_page() for compound pages")
>> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.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
>>
>>
> .
>