mm/damon/reclaim: validate min_region_size to be power of 2

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.

Link: https://lore.kernel.org/20260501013750.71704-3-aethernet65535@gmail.com
Signed-off-by: Liew Rui Yan <aethernet65535@gmail.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/damon/reclaim.c b/mm/damon/reclaim.c
index 7126d47fb8b2fa8730678d8b11e273c55501e84e..ed446d00ef1cf250175157ef660efe0d338d4c3c 100644 (file)
--- a/mm/damon/reclaim.c
+++ b/mm/damon/reclaim.c
@@ -210,6 +210,11 @@ 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;