Date:   Mon, 10 Jul 2023 09:57:15 -0400
From:   "Liam R. Howlett" <Liam.Howlett@...cle.com>
To:     Peng Zhang <zhangpeng.00@...edance.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, maple-tree@...ts.infradead.org
Subject: Re: [RESEND PATCH 3/8] maple_tree: make mas_validate_gaps() to check
 metadata

* Peng Zhang <zhangpeng.00@...edance.com> [230710 05:44]:
> 
> 
> 在 2023/7/7 22:45, Liam R. Howlett 写道:
> > * Peng Zhang <zhangpeng.00@...edance.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@...edance.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.

I'm saying we aren't checking that gaps beyond the node limit are zero.

I wasn't concerned about the meta_gap pointing beyond the node limit,
but it would probably be a good check too.


> > 
> > >   			}
> > >   		}
> > >   		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.

Yes, I think that's a good idea.  I don't believe we have a check for
this anywhere.

> 
> > 
> > > +		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@...ts.infradead.org
> > > https://lists.infradead.org/mailman/listinfo/maple-tree

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