Docs/admin-guide/mm/damon/reclaim: warn commit_inputs vs param updates race

Docs/admin-guide/mm/damon/reclaim: warn commit_inputs vs param updates race

Patch series "Docs/admin-guide/mm/damon: warn commit_inputs vs other
params race".

Writing 'Y' to the commit_inputs parameter of DAMON_RECLAIM and
DAMON_LRU_SORT, and writing other parameters before the commit_inputs
request is completely processed can cause race conditions.  While the
consequence can be bad, the documentation is not clearly describing that.
Add clear warnings.

The issue was discovered [1,2] by sashiko.

This patch (of 2):

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 in [1] by sashiko.

Link: https://lore.kernel.org/20260329153052.46657-2-sj@kernel.org
Link: https://lore.kernel.org/20260319161620.189392-3-objecting@objecting.org
Link: https://lore.kernel.org/20260319161620.189392-2-objecting@objecting.org
Fixes: 81a84182c343 ("Docs/admin-guide/mm/damon/reclaim: document 'commit_inputs' parameter")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 5.19.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>