[PATCH v5 0/2] mm/damon: validate min_region_size to be power of 2

[PATCH v5 0/2] mm/damon: validate min_region_size to be power of 2

[Liew Rui Yan]

Problem
=======
When a user sets an invalid 'addr_unit' (e.g., 3) via DAMON_LRU_SORT or
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.

Solution
========
Add an early validation in damon_lru_sort_apply_parameters() and
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.

Patch 1 fixes the issue for DAMON_LRU_SORT.
Patch 2 fixes the issue for DAMON_RECLAIM.

Changes from v4
(https://lore.kernel.org/20260410044259.95877-1-aethernet65535@gmail.com)
- Clarify this is only a minor user experience improvement.
- Remove Fixes: and Cc: stable tags.
Changes from v3
(https://lore.kernel.org/20260403052837.58063-1-aethernet65535@gmail.com)
- Improve commit message: clarify "unexpected termination".
- Add detailed User Impact with reason why kdamond cannot be restarted.
Changes from v2
(https://lore.kernel.org/20260402053756.26606-1-aethernet65535@gmail.com)
- Split the patch into two per-module patches.
- Add Fixes: and Cc: stable tags.
- Elaborate user impact and reproduction steps.
Changes from v1
(https://lore.kernel.org/20260331073231.30060-1-aethernet65535@gmail.com)
- Fix memory leak issue.
Changes from first attempt
(https://lore.kernel.org/20260327062627.66426-1-aethernet65535@gmail.com)
- Renamed the subject.
- Validate min_region_sz rather than addr_unit.

Liew Rui Yan (2):
  mm/damon/lru_sort: validate min_region_size to be power of 2
  mm/damon/reclaim: validate min_region_size to be power of 2

 mm/damon/lru_sort.c | 5 +++++
 mm/damon/reclaim.c  | 5 +++++
 2 files changed, 10 insertions(+)

-- 
2.53.0

[PATCH v5 1/2] mm/damon/lru_sort: validate min_region_size to be power of 2

[Liew Rui Yan]

Problem
=======
When a user sets an invalid 'addr_unit' (e.g., 3) via DAMON_LRU_SORT,
'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_LRU_SORT
2. Set addr_unit=3
3. Commit inputs via 'commit_inputs'
4. Observe kdamond termination

Solution
========
Add an early validation in damon_lru_sort_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/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;
-- 
2.53.0

Re: [PATCH v5 1/2] mm/damon/lru_sort: validate min_region_size to be power of 2

[SeongJae Park]

On Fri,  1 May 2026 09:37:49 +0800 Liew Rui Yan <aethernet65535@gmail.com> wrote:

> Problem
> =======
> When a user sets an invalid 'addr_unit' (e.g., 3) via DAMON_LRU_SORT,
> '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_LRU_SORT
> 2. Set addr_unit=3
> 3. Commit inputs via 'commit_inputs'
> 4. Observe kdamond termination
> 
> Solution
> ========
> Add an early validation in damon_lru_sort_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>

Reviewed-by: SeongJae Park <sj@kernel.org>


Thanks,
SJ

[...]

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

[Liew Rui Yan]

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

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

[SeongJae Park]

On Fri,  1 May 2026 09:37:50 +0800 Liew Rui Yan <aethernet65535@gmail.com> wrote:

> 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.

Looks good to me.

> 
> Signed-off-by: Liew Rui Yan <aethernet65535@gmail.com>

Reviewed-by: SeongJae Park <sj@kernel.org>


Thanks,
SJ

[...]