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Howlett" , "# 6 . 0 . x" , 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) [PATCH 2/2] Docs/admin-guide/mm/damon/lru_sort: warn commit_inputs vs param updates race Date: Sun, 29 Mar 2026 08:55:18 -0700 Message-ID: <20260329155518.48149-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260329154955.47813-1-sj@kernel.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: E7F244000E X-Stat-Signature: 38rb5qi5ij5yae7m3htp9nfyytiryjg5 X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1774799720-963701 X-HE-Meta: U2FsdGVkX1/nPwhmhdsGRI6/IVeUsxQONCMz97IohGZ20nhlK/Ocll8zAcjpjuiQ9HyELcS7RiJkDq8Ut3O1721beXUvsDSoaBqnZlLID4d5SV0ZJF2OhzjNtHX/Ih9tOhALb6LYILi2APoNmII8EnY2maOiu/GeUVATRGDu1Cb9OpZO7rPCxPVzWAfTSi6vOqhNoRFqG1A1HXvlwgmgsna3Q3JPEfj+H/xfZRrLGSS5mohu1cRcBO3Q7mNGJ6hU/4OuZzTaAU1XQlRdZRnoF90AuYo34fXMrxSRe3NNlQoWQ9l3rQwHJ2navbirwBNhxpfFf1gHR5wC+R0v/KONpeEonDmvrkx1qZXwAPHvh1tXM9i9e06bKsEeEF1nCqd3AfM5mzFidAh2glT8TcKHEtUiisNwt1Lt02UCWF/9c48QfK0oc0mIv2M70LkCo6kKX58r6+M4Vpo5q8B7afOzZyLzJcmTX8BZFSpwOX7qNnQBhrq+r53LVg/Md2tnkkusl3vjz/qZY9Xk1XvZ0483rWd5L4etvKXY4k+ODoIjIl2Lz+F5wF72i4Y4gXZMPnhNcOQU6KshdDD3cPMA4nKYD8ArQqwzlAyBU2Jx7OPD02GQaX4zqaF6wSjHmyR1q7kj1c5Tzgle7rl+UilfbgDXo8VI2rrEaIquMw5iRC/b7X4eWfDLhBD4zBtxyJPhFf8ltZnW5a6Qs5RzUEInBNy5Shc59MvD4r6sOu+HhYjSFl6wArTOhgc++WPThhz7vFbg8Y8L1edCycyz1hKAVOeUAWOKRzrKUhqFkYOXf3htFI3WWamyj6ygoRQje1wQy///9M9hAGkJvAQ796Y0oYBcmU1ZN554lZpAVUtbeqbP3bmElGh3zSrsbgh+0/hYafthwwjeZmQtEh0TZoiGNgNcB2BOmarnELmLPmOYx2kueCOjqFkCPlOYTShL1GF4AWsX6M/46qrHQdze4McyxOD taHAE1NA qUPgjhY+M71PkEB4= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, 29 Mar 2026 08:49:54 -0700 SeongJae Park wrote: > Forwarding Sashiko review for doing discussions via mails. > > # review url: https://sashiko.dev/#/patchset/20260329153052.46657-3-sj@kernel.org > # start of sashiko.dev inline review > commit 7f5e14b7be3b4aea36d62a6c529ef25dde22e973 > Author: SeongJae Park > > Docs/admin-guide/mm/damon/lru_sort: warn commit_inputs vs param updates race > > This commit updates the DAMON LRU_SORT documentation to warn users against > modifying module parameters while the kdamond thread is processing a > commit_inputs request. It states that violating this rule can cause races > and 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..14cc6b2db897 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 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. > > Is it safe to rely on userspace following documentation to prevent kernel > data races? > > The kernel is generally expected to be robust against concurrent or unexpected > userspace inputs. Does addressing a data race with a documentation warning > leave the kernel vulnerable to crashes or instability if a user ignores this > rule? > > Could this underlying race condition be resolved with proper synchronization, > such as locks or mutexes, rather than documenting the undefined behavior? I answered same question on the previous version of this patch. In short, I think this is ok for stable kernels. For mainline, Liew's patch [1] that can fix this issue together is on the way. [1] https://lore.kernel.org/20260329075415.36775-1-aethernet65535@gmail.com Thanks, SJ [...]