[PATCH] mm/damon: validate addr_unit to be power of 2

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

Problem
=======
The 'addr_unit' must be a power of 2 for correct address alignment
calculations. Previously, writing a non-power-of-2 value
(e.g., addr_unit=3) would be accepted by the sysfs store callback, but
cause kdamond to exit unexpectedly during parameter application, failing
silently without returning an error to userspace.

Solution
========
Add an is_power_of_2() check in damon_commit_ctx() to reject invalid
inputs immediately with -EINVAL. 

When damon_commit_ctx() fails, the kdamond thread terminates as
designed.

The issue is found by sashiko [1].

[1] https://lore.kernel.org/20260325025317.86571-1-sj@kernel.org

Signed-off-by: Liew Rui Yan <aethernet65535@gmail.com>
---
 mm/damon/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index db6c67e52d2b..6bad85a47a79 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -1330,6 +1330,8 @@ int damon_commit_ctx(struct damon_ctx *dst, struct damon_ctx *src)
 	dst->maybe_corrupted = true;
 	if (!is_power_of_2(src->min_region_sz))
 		return -EINVAL;
+	if (!src->addr_unit || !is_power_of_2(src->addr_unit))
+		return -EINVAL;
 
 	err = damon_commit_schemes(dst, src);
 	if (err)
-- 
2.53.0