DAMON_LRU_SORT 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/20260319161620.189392-2-objecting@objecting.org

Fixes: 6acfcd0d7524 ("Docs/admin-guide/damon: add a document for DAMON_LRU_SORT")
Cc: <stable@vger.kernel.org> # 6.0.x
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 Documentation/admin-guide/mm/damon/lru_sort.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/admin-guide/mm/damon/lru_sort.rst b/Documentation/admin-guide/mm/damon/lru_sort.rst
index 797962a459e6..5b8e16394228 100644
--- a/Documentation/admin-guide/mm/damon/lru_sort.rst
+++ b/Documentation/admin-guide/mm/damon/lru_sort.rst
@@ -79,6 +79,10 @@ 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_LRU_SORT will be disabled.
 
+Once ``Y`` is written to this parametr, the user must not write to any
+parameters until reading ``commit_inputs`` again returns ``N``.  If users
+violate this rule, the kernel can do undefined behaviors.
+
 active_mem_bp
 -------------
 
-- 
2.47.3

Forwarding Sashiko review for doing discussions via mails.

# review url: https://sashiko.dev/#/patchset/20260328172415.49940-3-sj@kernel.org
# start of sashiko.dev inline review
commit 0a9a055d4225a92c337c76fef97bfcdca5d9508f
Author: SeongJae Park <sj@kernel.org>
Docs/admin-guide/mm/damon/lru_sort: warn commit_inputs vs param updates race

This patch adds documentation warning users about a data race in DAMON_LRU_SORT
when modifying module parameters while the kdamond thread is reading them. It
states that violating this rule can cause undefined behavior in the kernel.

Link: https://lore.kernel.org/20260319161620.189392-2-objecting@objecting.org

> diff --git a/Documentation/admin-guide/mm/damon/lru_sort.rst b/Documentation/admin-guide/mm/damon/lru_sort.rst
> index a7dea7c75a9b..3eaa3786c8ab 100644
> --- a/Documentation/admin-guide/mm/damon/lru_sort.rst
> +++ b/Documentation/admin-guide/mm/damon/lru_sort.rst
> @@ -79,6 +79,10 @@ of parametrs 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_LRU_SORT will be disabled.
>  
> +Once ``Y`` is written to this parametr, the user must not write to any
                                  ^^^^^^^^

This isn't a bug, but there is a typo here (parametr).

> +parameters until reading ``commit_inputs`` again returns ``N``.  If users
> +violate this rule, the kernel can do undefined behaviors.
                                        ^^^^^^^^^^^^^^^^^^^

Should this data race be fixed in the kernel code itself rather than just
documented?

The kernel generally should not exhibit undefined behavior, memory corruption,
or crashes due to concurrent sysfs or module parameter writes, even if those
writes are restricted to root users. Could the underlying code be updated
with proper synchronization to safely handle concurrent updates instead?

> +
>  active_mem_bp
>  -------------
>  


# end of sashiko.dev inline review
# review url: https://sashiko.dev/#/patchset/20260328172415.49940-3-sj@kernel.org
#
# hkml [1] generated a draft of this mail.  It can be regenerated
# using below command:
#
#     hkml patch sashiko_dev --for_forwarding \
#             20260328172415.49940-3-sj@kernel.org
#
# [1] https://github.com/sjp38/hackermail

Sent using hkml (https://github.com/sjp38/hackermail)

On Sat, 28 Mar 2026 10:35:04 -0700 SeongJae Park <sj@kernel.org> wrote:

> Forwarding Sashiko review for doing discussions via mails.

All comments are same to that for DAMON_RECLAIM.  Please refer to
https://lore.kernel.org/20260328174852.53338-1-sj@kernel.org for my response.


Thanks,
SJ

[...]