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Howlett" , "# 5 . 19 . x" , Andrew Morton , David Hildenbrand , Jonathan Corbet , Lorenzo Stoakes , Michal Hocko , Mike Rapoport , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , damon@lists.linux.dev, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: (sashiko review) [RFC PATCH 1/2] Docs/admin-guide/mm/damon/reclaim: warn commit_inputs vs param updates race Date: Sat, 28 Mar 2026 10:34:45 -0700 Message-ID: <20260328173446.53021-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260328172415.49940-2-sj@kernel.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: D8632C000A X-Stat-Signature: 7g1iuwosqm6wrdcjre39i91o6qe41e4u X-Rspam-User: X-HE-Tag: 1774719288-80452 X-HE-Meta: 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 R5ESvBOa fhAemf+g0Fgq6LJgA/ksZnmVSiiwfJHokytPD2uaOkh1+VcsSnI1xFil5qN/JYxHwccBJgxy2h3QKa1ZfEuSYDXf0tvN1SN15IpllEWzV8pxdXVZZ9CllDWkjVq4SKq840NbPQHPS/W6U532yIjOYPm9jMICna7NeO1axtynaAfVjUURwWgC8+ULQ2XYS+q962GlqESE/JpaC841SPkZTrBN3VYUwOGeHkJ0HJo7FqNWLPnWWwDOLTJJC38RWfM/o6V2h2neosVh3diOVCUlxxlXQ3UoLOkOLMbDX7qxfXBP4Ydtxe/o1CeSpZNHxVAdoTvL5rdR98kVOib7WUeX0BoOcJu4H5FnmWWRLT6RIasAwG2i786fCRzbHFMpz+LnCaMp3qzjY0/Y2yFb0sfi5RXCATNiz2ijnyrfGQgFTFdq0dSA= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Forwarding Sashiko review for doing discussions via mails. # review url: https://sashiko.dev/#/patchset/20260328172415.49940-2-sj@kernel.org # start of sashiko.dev inline review commit 8b189801fc104c5ecc412454a3d8db6a3faf27d6 Author: SeongJae Park Docs/admin-guide/mm/damon/reclaim: warn commit_inputs vs param updates race This commit adds documentation warning users not to write to module parameters while commit_inputs is in progress. This warning is intended to help users avoid a race condition that can cause undefined kernel behavior. Link: https://lore.kernel.org/20260319161620.189392-3-objecting@objecting.org > diff --git a/Documentation/admin-guide/mm/damon/reclaim.rst b/Documentation/admin-guide/mm/damon/reclaim.rst > --- 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 parametr, the user must not write to any This isn't a bug, but there is a typo ("parametr") in this line. > +parameters until reading ``commit_inputs`` again returns ``N``. If users > +violate this rule, the kernel can do undefined behaviors. Is it acceptable to document a race condition that leads to undefined behavior instead of fixing it? Even if the module parameter interface is restricted to root, user space shouldn't be able to trigger kernel undefined behavior (which could lead to memory corruption or crashes) simply by writing to module parameters concurrently. Should the underlying race condition in DAMON_RECLAIM be fixed with proper synchronization rather than relying on userspace adherence to a documentation warning? This isn't a bug, but the phrasing "can do undefined behaviors" is slightly awkward. Rephrasing to "may exhibit undefined behavior" might be more natural. # end of sashiko.dev inline review # review url: https://sashiko.dev/#/patchset/20260328172415.49940-2-sj@kernel.org # # hkml [1] generated a draft of this mail. It can be regenerated # using below command: # # hkml patch sashiko_dev --for_forwarding \ # 20260328172415.49940-2-sj@kernel.org # # [1] https://github.com/sjp38/hackermail Sent using hkml (https://github.com/sjp38/hackermail)