linux-kernel - Re: [PATCH] maple_tree: not necessary to filter MAPLE_PARENT

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Date:   Thu, 17 Nov 2022 03:45:52 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     Liam Howlett <liam.howlett@...cle.com>
Cc:     Wei Yang <richard.weiyang@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] maple_tree: not necessary to filter MAPLE_PARENT_ROOT
 since it is not a root

On Tue, Nov 15, 2022 at 02:31:15PM +0000, Liam Howlett wrote:
>* Wei Yang <richard.weiyang@...il.com> [221112 19:56]:
>> Root node is return at the beginning, so we are sure bit 0 is not set.
>> 
>> Signed-off-by: Wei Yang <richard.weiyang@...il.com>
>> CC: Liam R. Howlett <Liam.Howlett@...cle.com>
>> ---
>>  lib/maple_tree.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
>> index 9aad98c24f3e..f8c4755e7c75 100644
>> --- a/lib/maple_tree.c
>> +++ b/lib/maple_tree.c
>> @@ -436,7 +436,7 @@ enum maple_type mte_parent_enum(struct maple_enode *p_enode,
>>  		return 0; /* Validated in the caller. */
>>  
>>  	p_type &= MAPLE_NODE_MASK;
>> -	p_type = p_type & ~(MAPLE_PARENT_ROOT | mte_parent_slot_mask(p_type));
>> +	p_type = p_type & ~mte_parent_slot_mask(p_type);
>
>I think there is a larger cleanup that can be done here.  It looks like
>mte_parent_enum() is called from one location and that location is a
>wrapper.
>
>The check for the root bit should also probably trigger a WARN_ON() and
>still return 0.  I don't think the callers are doing enough to validate
>it - although they should never reach this function with a root node.
>And, in fact, I am not doing enough in the test code since I didn't
>guard this correctly in the verification of the parent slot before
>calling this function.
>
>Thanks for pointing this out.  I will send out a patch to clean this up
>shortly.
>

Yep, look forward your cleanup.

While I have a question here. We get 4 types in maple_type, here we just
return two of them. This means the other two is not possible to be parent
node, right?

>>  
>>  	switch (p_type) {
>>  	case MAPLE_PARENT_RANGE64: /* or MAPLE_PARENT_ARANGE64 */
>> -- 
>> 2.33.1
>> 

-- 
Wei Yang
Help you, Help me