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Message-ID: <3c260876-2ee5-7659-0c02-17a68277567f@bytedance.com>
Date:   Mon, 10 Jul 2023 17:44:47 +0800
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Subject: Re: [RESEND PATCH 3/8] maple_tree: make mas_validate_gaps() to check
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To:     "Liam R. Howlett" <Liam.Howlett@Oracle.com>
References: <20230707101057.29326-1-zhangpeng.00@bytedance.com>
 <20230707101057.29326-4-zhangpeng.00@bytedance.com>
 <20230707144550.eavqm7zcr6dofl73@revolver>
From:   Peng Zhang <zhangpeng.00@bytedance.com>
Cc:     Peng Zhang <zhangpeng.00@bytedance.com>, akpm@linux-foundation.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        maple-tree@lists.infradead.org
In-Reply-To: <20230707144550.eavqm7zcr6dofl73@revolver>
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在 2023/7/7 22:45, Liam R. Howlett 写道:
> * Peng Zhang <zhangpeng.00@bytedance.com> [230707 06:11]:
>> Make mas_validate_gaps() check whether the offset in the metadata points
>> to the largest gap. By the way, simplify this function.
>>
>> Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
>> ---
>>   lib/maple_tree.c | 68 +++++++++++++++++++++++-------------------------
>>   1 file changed, 33 insertions(+), 35 deletions(-)
>>
>> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
>> index 6a8982146338..1fe8b6a787dd 100644
>> --- a/lib/maple_tree.c
>> +++ b/lib/maple_tree.c
>> @@ -6983,15 +6983,16 @@ EXPORT_SYMBOL_GPL(mt_dump);
>>   static void mas_validate_gaps(struct ma_state *mas)
>>   {
>>   	struct maple_enode *mte = mas->node;
>> -	struct maple_node *p_mn;
>> +	struct maple_node *p_mn, *node = mte_to_node(mte);
>> +	enum maple_type mt = mte_node_type(mas->node);
>>   	unsigned long gap = 0, max_gap = 0;
>>   	unsigned long p_end, p_start = mas->min;
>> -	unsigned char p_slot;
>> +	unsigned char p_slot, offset;
>>   	unsigned long *gaps = NULL;
>> -	unsigned long *pivots = ma_pivots(mte_to_node(mte), mte_node_type(mte));
>> +	unsigned long *pivots = ma_pivots(node, mt);
>>   	int i;
>>   
>> -	if (ma_is_dense(mte_node_type(mte))) {
>> +	if (ma_is_dense(mt)) {
>>   		for (i = 0; i < mt_slot_count(mte); i++) {
>>   			if (mas_get_slot(mas, i)) {
>>   				if (gap > max_gap)
>> @@ -7004,52 +7005,51 @@ static void mas_validate_gaps(struct ma_state *mas)
>>   		goto counted;
>>   	}
>>   
>> -	gaps = ma_gaps(mte_to_node(mte), mte_node_type(mte));
>> +	gaps = ma_gaps(node, mt);
>>   	for (i = 0; i < mt_slot_count(mte); i++) {
>> -		p_end = mas_logical_pivot(mas, pivots, i, mte_node_type(mte));
>> +		p_end = mas_logical_pivot(mas, pivots, i, mt);
>>   
>>   		if (!gaps) {
>> -			if (mas_get_slot(mas, i)) {
>> -				gap = 0;
>> -				goto not_empty;
>> -			}
>> -
>> -			gap += p_end - p_start + 1;
>> +			if (!mas_get_slot(mas, i))
>> +				gap = p_end - p_start + 1;
>>   		} else {
>>   			void *entry = mas_get_slot(mas, i);
>>   
>>   			gap = gaps[i];
>> -			if (!entry) {
>> -				if (gap != p_end - p_start + 1) {
>> -					pr_err("%p[%u] -> %p %lu != %lu - %lu + 1\n",
>> -						mas_mn(mas), i,
>> -						mas_get_slot(mas, i), gap,
>> -						p_end, p_start);
>> -					mt_dump(mas->tree, mt_dump_hex);
>> -
>> -					MT_BUG_ON(mas->tree,
>> -						gap != p_end - p_start + 1);
>> -				}
>> -			} else {
>> -				if (gap > p_end - p_start + 1) {
>> -					pr_err("%p[%u] %lu >= %lu - %lu + 1 (%lu)\n",
>> -					mas_mn(mas), i, gap, p_end, p_start,
>> -					p_end - p_start + 1);
>> -					MT_BUG_ON(mas->tree,
>> -						gap > p_end - p_start + 1);
>> -				}
>> +			MT_BUG_ON(mas->tree, !entry);
>> +
>> +			if (gap > p_end - p_start + 1) {
>> +				pr_err("%p[%u] %lu >= %lu - %lu + 1 (%lu)\n",
>> +				mas_mn(mas), i, gap, p_end, p_start,
>> +				p_end - p_start + 1);
>> +				MT_BUG_ON(mas->tree,
>> +					gap > p_end - p_start + 1);
> 
> Your change above points out that we are not verifying all gaps are zero
> in non-leaf nodes after p_end >= mas->max.  If we don't have a 'no gap'
> indicator then this may be an issue, or maybe it already is an issue?
If we don't have a 'no gap' indicator, why is there an issue? Are you
worried that meta_gap is wrongly pointing to the gap after the node
limit? If so we can verify that meta_gap points to a gap within the node
limit.
> 
>>   			}
>>   		}
>>   
>>   		if (gap > max_gap)
>>   			max_gap = gap;
>> -not_empty:
>> +
>>   		p_start = p_end + 1;
>>   		if (p_end >= mas->max)
>>   			break;
>>   	}
>>   
>>   counted:
>> +	if (mt == maple_arange_64) {
> 
> We could loop through the remainder of the gaps here pretty easily.
In this way, it can be verified that the gaps after the node limit are
0.

> 
>> +		offset = ma_meta_gap(node, mt);
>> +		if (offset > mt_slots[mt]) {
>> +			pr_err("gap offset %p[%u] is invalid\n", node, offset);
>> +			MT_BUG_ON(mas->tree, 1);
>> +		}
>> +
>> +		if (gaps[offset] != max_gap) {
>> +			pr_err("gap %p[%u] is not the largest gap %lu\n",
>> +			       node, offset, max_gap);
>> +			MT_BUG_ON(mas->tree, 1);
>> +		}
>> +	}
>> +
>>   	if (mte_is_root(mte))
>>   		return;
>>   
>> @@ -7059,10 +7059,8 @@ static void mas_validate_gaps(struct ma_state *mas)
>>   	if (ma_gaps(p_mn, mas_parent_type(mas, mte))[p_slot] != max_gap) {
>>   		pr_err("gap %p[%u] != %lu\n", p_mn, p_slot, max_gap);
>>   		mt_dump(mas->tree, mt_dump_hex);
>> +		MT_BUG_ON(mas->tree, 1);
>>   	}
>> -
>> -	MT_BUG_ON(mas->tree,
>> -		  ma_gaps(p_mn, mas_parent_type(mas, mte))[p_slot] != max_gap);
>>   }
>>   
>>   static void mas_validate_parent_slot(struct ma_state *mas)
>> -- 
>> 2.20.1
>>
>>
>> -- 
>> maple-tree mailing list
>> maple-tree@lists.infradead.org
>> https://lists.infradead.org/mailman/listinfo/maple-tree