Re: [PATCH v3 2/2] test_maple_tree: test maple_range_64 node in RCU mode

[Florian Schmaus]

> This commit adds a test that builds two maple_range_64 trees in RCU
> mode.  The first tree has a root that is a full maple_range_64 node and
> ensures that the destruction under RCU does not misinterpret the last
> slot as metadata. 226 insertions produce such a root on a 64-bit build.
> 
> The second tree is a height 3 tree whose root holds 15 child pointers
> and metadata in its last slot, so every slot is non-zero and ensures
> that the destruction under RCU does not descend into the metadata slot.
> 3166 insertions produce such a tree on a 64-bit build.
> 
> Signed-off-by: Dimitris Charisis <dchar@xxxxxxxxxxxxxxxxx>
>
> diff --git a/lib/test_maple_tree.c b/lib/test_maple_tree.c
> index b9367c61e8b5..fb40e193a3cb 100644
> --- a/lib/test_maple_tree.c
> +++ b/lib/test_maple_tree.c
> @@ -3710,6 +3710,36 @@ static noinline void __init alloc_cyclic_testing(struct maple_tree *mt)
>  	MT_BUG_ON(mt, ret != 1);
>  }
>  
> +static noinline void __init check_range64_in_rcu(struct maple_tree *mt)
> +{
> +	unsigned long i;
> +	unsigned long nr_entries = 226; /* Build a full maple_range_64 root node */
> +
> +	MT_BUG_ON(mt, !mtree_empty(mt));
> +	mt_init_flags(mt, MT_FLAGS_USE_RCU);
> +
> +	for (i = 0; i < nr_entries; i++) {
> +		MT_BUG_ON(mt, mtree_test_insert_range(mt, i*10, i*10 + 9,
> +						      xa_mk_value(i)));
> +	}
> +
> +	mtree_destroy(mt);
> +	rcu_barrier();
> +
> +	nr_entries = 3166; /* Height 3. Root has 15 children + metadata */
> +
> +	MT_BUG_ON(mt, !mtree_empty(mt));
> +	mt_init_flags(mt, MT_FLAGS_USE_RCU);
> +
> +	for (i = 0; i < nr_entries; i++) {
> +		MT_BUG_ON(mt, mtree_test_insert_range(mt, i*10, i*10 + 9,
> +						      xa_mk_value(i)));
> +	}
> +
> +	mtree_destroy(mt);
> +	rcu_barrier();

This case passes on an unfixed kernel.

The bug that exists today requires a non-root node with 15 children and a
tree of height 4. The size-2768 test case in my series covers that. You can
find my test at

https://lore.kernel.org/all/20261015-maple-tree-fix-slab-corruption-v1-3-160d97f7304c@xxxxxxxxxxx/

and may fold it into your check_range64_in_rcu(). It fails without your (or
my) fix and succeed with.

-- 
Florian Schmaus <florian.schmaus@xxxxxxxxxxx>