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b=eomREd/jqdFfEgIBTkw87GKHW8I0aNQbEYgqPC+XhMuQfF2kvqLQHuoDRkVWKW8Um h/kWbDGPyuzYBZ9C0uO7GVGW9GkEayqY6gWg8tx/KLP0ob8veYHtN+HgVlApO0Nt/8 pashGIOoSOk27LBlcMGTWhdXFRBKtPQoIGzHA19aJ3BcK86worHf/tRgXwAfjZoy+9 H+Lkytu5tfiU2+lMFJRsJ+SEDBGG8vVOUKTzOxEegmp4KRpGy03h5ob5Di7vvErmuO rlRcia4W1GnwI5pHxpDwSEpNjcLXIY6tmJhMcCLGum7zrR+2OitqMapuYcDiQXwIyN Qj4Qyt1OaS6Cw== From: SJ Park To: Andrew Morton Cc: SJ Park , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 05/10] mm/damon/core: document damon_call()/damon_start() race hang issue Date: Thu, 17 Sep 2026 07:22:03 -0700 Message-ID: <20260917142210.90829-6-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260917142210.90829-1-sj@kernel.org> References: <20260917142210.90829-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: E36F4100002 X-Stat-Signature: og3xj8g88khsyzjmjw74d7ctxphmqahe X-Rspamd-Server: rspam01 X-HE-Tag: 1789654940-857506 X-HE-Meta: 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 58d7agkn QtQPthd6w6TmadNs0s5h9PPFE3OWnlBJ/9KTvRvoK5I+0L3n3KyknjxEOEpXYK2rDXBncVBFzGSm6lw/Mtvro7lOoLt+5KmrGVSmRjBczjZ+lwyB/X72nrhusGZBjocyVhXzd+/mLJdJ7T6GDk39Di5Y2V3VYnppMPwUpZrQXeyP0CRZ9IlQARMjM+m1bqb4f0Bt6lDsCH9V0C0Z6fwLMGDuiF2/PW1suyNTfxoNW8L1T1zVgeFQ5uucb7d7bsEKlvrOuaRUiY3or0SXr92e/DKyJYg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Let's suppose damon_start() and damon_call() are executed in parallel for the same DAMON context. Then, damon_call() could show ctx->damon_calls_obsolete set while ctx->kdamond is unset. If damon_start() sets ctx->kdamond before damon_call() starts the cancelling, damon_call() can indefinitely hang. No DAMON API caller does such parallel execution of damon_start() and damon_call(), so the issue doesn't exist. But who knows what will happen in future. Add a clarification comment for caution. Signed-off-by: SJ Park --- mm/damon/core.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/mm/damon/core.c b/mm/damon/core.c index c63b09d4a2d0d..2258b72da7a78 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2258,6 +2258,9 @@ int damon_kdamond_pid(struct damon_ctx *ctx) * * When this function is failed, the @ctx is guaranteed to be stopped. * + * This function should not be called in parallel to damon_start() for the + * @ctx. In the case, this function could indefinitely hang. + * * Return: 0 on success, negative error code otherwise. */ int damon_call(struct damon_ctx *ctx, struct damon_call_control *control) -- 2.47.3