Re: [PATCH v3 1/2] mm/damon/lru_sort: validate min_region_size to be power of 2

Quanmin Yan
2026-04-03T08:59:41Z

Hi Liew,

在 2026/4/3 13:23, Liew Rui Yan 写道:
> The damon_commit_ctx() checks if 'min_region_sz' is a power-of-2.
> However, if an invalid input is provided via the DAMON_LRU_SORT
> interface, the validation failure occurs too late, causing kdamond to
> terminate unexpectedly.

I'm a little confused, what does "causing kdamond to terminate
unexpectedly" mean? The damon_lru_sort_apply_parameters function will
eventually call damon_commit_ctx, and the power-of-2 check is always
performed. Is the early check here to prevent some more broken case
or am I missing something?

Thanks,
Quanmin Yan

> To reproduce:
> 1. Enable DAMON_LRU_SORT.
> 2. Set an invalid 'addr_unit' (e.g., addr_unit=3) so that
> 'min_region_sz = DAMON_MIN_REGION_SZ / addr_unit' becomes
> non-power-of-2.
> 3. Commit parameters, and observe kdamond termination.
>
> This patch adds an early check in damon_lru_sort_apply_parameters() to
> validate 'min_region_sz' and return -EINVAL immediately if it is not
> a power-of-2, preventing unexpected kdamond termination.
>
> Fixes: 2e0fe9245d6b ("mm/damon/lru_sort: support addr_unit for DAMON_LRU_SORT")
> Cc: <stable@vger.kernel.org> # 6.18.x
> Signed-off-by: Liew Rui Yan <aethernet65535@gmail.com>
> ---
> mm/damon/lru_sort.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/mm/damon/lru_sort.c b/mm/damon/lru_sort.c
> index 554559d72976..3fd176ef9d9c 100644
> --- a/mm/damon/lru_sort.c
> +++ b/mm/damon/lru_sort.c
> @@ -294,6 +294,11 @@ static int damon_lru_sort_apply_parameters(void)
> param_ctx->addr_unit = addr_unit;
> param_ctx->min_region_sz = max(DAMON_MIN_REGION_SZ / addr_unit, 1);
>
> + if (!is_power_of_2(param_ctx->min_region_sz)) {
> + err = -EINVAL;
> + goto out;
> + }
> +
> if (!damon_lru_sort_mon_attrs.sample_interval) {
> err = -EINVAL;
> goto out;