[PATCH v5 2/2] mm/damon/reclaim: validate min_region_size to be power of 2

[Liew Rui Yan <aethernet65535@gmail.com>]

Problem
=======
When a user sets an invalid 'addr_unit' (e.g., 3) via DAMON_RECLAIM,
'min_region_sz' becomes a non-power-of-2 value. While damon_commit_ctx()
correctly detects this and returns -EINVAL, it sets the
'maybe_corrupted' flag during this process.

This flag causes the running kdamond to terminate. While the termination
is a safety measure, it is suboptimal in this case because the error is
just a simple invalid input from the user, which shouldn't neccessitate
stopping the kdamond.

Reproduction
============
1. Enable DAMON_RECLAIM
2. Set addr_unit=3
3. Commit inputs via 'commit_inputs'
4. Observe kdamond termination

Solution
========
Add an early validation in damon_reclaim_apply_parameters() to check
'min_region_sz' before any state change occurs. If it is non-power-of-2,
return -EINVAL immediately, preventing 'maybe_corrupted' from being set.

Signed-off-by: Liew Rui Yan <aethernet65535@gmail.com>
---
 mm/damon/reclaim.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/damon/reclaim.c b/mm/damon/reclaim.c
index 86da14778658..2747eef5919d 100644
--- a/mm/damon/reclaim.c
+++ b/mm/damon/reclaim.c
@@ -204,6 +204,11 @@ static int damon_reclaim_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_reclaim_mon_attrs.aggr_interval) {
 		err = -EINVAL;
 		goto out;
-- 
2.53.0