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From: majianpeng <majianpeng@gmail.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-mm <linux-mm@kvack.org>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: Re: [PATCH 2/3] mm/kmemleak.c: Use list_for_each_entry_safe to reconstruct function scan_gray_list
Date: Mon, 3 Jun 2013 08:58:49 +0800	[thread overview]
Message-ID: <201306030858459339090@gmail.com> (raw)
In-Reply-To: 20130530144028.GF23631@arm.com

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>On Tue, May 14, 2013 at 12:49:44PM +0100, majianpeng wrote:
>> Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
>> ---
>>  mm/kmemleak.c | 8 +-------
>>  1 file changed, 1 insertion(+), 7 deletions(-)
>> 
>> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
>> index b1525db..f0ece93 100644
>> --- a/mm/kmemleak.c
>> +++ b/mm/kmemleak.c
>> @@ -1225,22 +1225,16 @@ static void scan_gray_list(void)
>>  	 * from inside the loop. The kmemleak objects cannot be freed from
>>  	 * outside the loop because their use_count was incremented.
>>  	 */
>> -	object = list_entry(gray_list.next, typeof(*object), gray_list);
>> -	while (&object->gray_list != &gray_list) {
>> +	list_for_each_entry_safe(object, tmp, &gray_list, gray_list) {
>>  		cond_resched();
>>  
>>  		/* may add new objects to the list */
>>  		if (!scan_should_stop())
>>  			scan_object(object);
>>  
>> -		tmp = list_entry(object->gray_list.next, typeof(*object),
>> -				 gray_list);
>> -
>>  		/* remove the object from the list and release it */
>>  		list_del(&object->gray_list);
>>  		put_object(object);
>> -
>> -		object = tmp;
>>  	}
>>  	WARN_ON(!list_empty(&gray_list));
>
>I tried this patch for a few days and I hit the WARN_ON after the loop.
>During scanning, new entries may be added at the end of the loop but we
>need to loop until all the entries have been removed. I probably had a
>reason why I had the 'while' loop.
>
>The key difference is that list_for_each_entry_safe() gets the next
>entry (n or tmp above) before scan_object() and it may hit the end of
>the list. However, scan_object() may do a list_add_tail(&gray_list)
>hence we need to get the next entry after this function.
>
>Basically list_for_each_entry_safe() is not safe with tail additions.
>I'll revert this patch (hasn't reached mainline anyway).
>
Ok, i see. 
Thanks!
>Thanks.
>
>-- 
>CatalinN‹§²æìr¸›zǧu©ž²Æ {\b­†éì¹»\x1c®&Þ–)îÆi¢žØ^n‡r¶‰šŽŠÝ¢j$½§$¢¸\x05¢¹¨­è§~Š'.)îÄÃ,yèm¶ŸÿÃ\f%Š{±šj+ƒðèž×¦j)Z†·Ÿ

      reply	other threads:[~2013-06-03  0:58 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-05-14 11:49 [PATCH 2/3] mm/kmemleak.c: Use list_for_each_entry_safe to reconstruct function scan_gray_list majianpeng
2013-05-30 14:40 ` Catalin Marinas
2013-06-03  0:58   ` majianpeng [this message]

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