[PATCH 1/2] Docs/admin-guide/mm/damon/reclaim: warn commit_inputs vs param updates race

SeongJae Park
2026-03-29T15:30:56Z

DAMON_RECLAIM handles commit_inputs request inside kdamond thread,
reading the module parameters. If the user updates the module
parameters while the kdamond thread is reading those, races can happen.
To avoid this, the commit_inputs parameter shows whether it is still in
the progress, assuming users wouldn't update parameters in the middle of
the work. Some users might ignore that. Add a warning about the
behavior.

The issue was discovered [1] by sashiko.

[1] https://lore.kernel.org/20260319161620.189392-3-objecting@objecting.org

Fixes: 81a84182c343 ("Docs/admin-guide/mm/damon/reclaim: document 'commit_inputs' parameter")
Cc: <stable@vger.kernel.org> # 5.19.x
Signed-off-by: SeongJae Park <sj@kernel.org>
---
Documentation/admin-guide/mm/damon/reclaim.rst | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/Documentation/admin-guide/mm/damon/reclaim.rst b/Documentation/admin-guide/mm/damon/reclaim.rst
index a100216f3a72..17e938c319e3 100644
--- a/Documentation/admin-guide/mm/damon/reclaim.rst
+++ b/Documentation/admin-guide/mm/damon/reclaim.rst
@@ -71,6 +71,10 @@ of parameters except ``enabled`` again. Once the re-reading is done, this
parameter is set as ``N``. If invalid parameters are found while the
re-reading, DAMON_RECLAIM will be disabled.

+Once ``Y`` is written to this parameter, the user must not write to any
+parameters until reading ``commit_inputs`` again returns ``N``. If users
+violate this rule, the kernel may exhibit undefined behavior.
+
min_age
-------

--
2.47.3