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Howlett" , "# 6 . 0 . 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 2/2] Docs/admin-guide/mm/damon/lru_sort: warn commit_inputs vs param updates race Date: Sat, 28 Mar 2026 10:35:04 -0700 Message-ID: <20260328173504.53129-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260328172415.49940-3-sj@kernel.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 2144E20002 X-Stat-Signature: 1a3psbd7r59mf5mgon5mcpgwcy8tf7wd X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1774719306-977421 X-HE-Meta: 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 ffUg+aJN v8CGh1gNICftIg5GUxkhKxHogFv3WkZseiWwCUOvBp4l5/uppmHf0JPA0D0CkJHPpFBOKj0d24pkEAfJ5BdTdZe4vpEI72sDaL/rMg8NUCq2hY2oxKJIDwua7C1XJzY+88Txlp2aSnyqIff783PuC2Gq/QoerjRuub9xMg6fCPQizQGbITuOP9cl911qzHTL+578WL/18xVIv9YMZTyuw4m0XIe+ORTtV6T9nAY8tGWGcsItVGr0Wv1E7PZ29UsLTINmjy+s0K/XPXIkQ19wg7p2MWLrEmMhKpHVPXLe/fFDS/N7ErpugQ8WiBLC3iJ1bFZBslV04UuPKlqWqTCGKAvfqE9rURKF1RpCwKBmlczlSTVeCe92w1Rv/NFovEGpklVu3MF4XVt9ol4Bu6LrNPuB997123XGa/A8eNBfsmZ3cFnE= 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/20260328172415.49940-3-sj@kernel.org # start of sashiko.dev inline review commit 0a9a055d4225a92c337c76fef97bfcdca5d9508f Author: SeongJae Park 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)