From: SeongJae Park Date: Sun, 29 Mar 2026 15:30:49 +0000 (-0700) Subject: Docs/admin-guide/mm/damon/reclaim: warn commit_inputs vs param updates race X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=0beba407d4585a15b0dc09f2064b5b3ddcb0e857;p=thirdparty%2Fkernel%2Flinux.git 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 [1] Link: https://lore.kernel.org/20260319161620.189392-2-objecting@objecting.org [3] Fixes: 81a84182c343 ("Docs/admin-guide/mm/damon/reclaim: document 'commit_inputs' parameter") Signed-off-by: SeongJae Park Cc: # 5.19.x Signed-off-by: Andrew Morton --- diff --git a/Documentation/admin-guide/mm/damon/reclaim.rst b/Documentation/admin-guide/mm/damon/reclaim.rst index 47854c461706c..d7a0225b49508 100644 --- a/Documentation/admin-guide/mm/damon/reclaim.rst +++ b/Documentation/admin-guide/mm/damon/reclaim.rst @@ -71,6 +71,10 @@ 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_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 -------