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b=K51/4QtDTuI+oO9+RACODBQv8TubJPnAUtItpnPP6GukNKjppgbjKYWcNGcqCZ6Yv 9VfBdalwvsB4kFJWZBKs/UUqhIT+aZjDy0kmv/40J69p1gLXyWm5gbaBfMlckAx8YI N94b7jc5WVLsE4xfBn+SxUHy/9umzdyJgEmzk4Vw5nKQWTmSngH2RPElybq3mYEQeB bSCm9D7/YAZ0e8FWFxmnHoHadjjOe/ztB1tMiYmxpICjWbT0gy3zg/G3KOp5ujn9l4 mBnNmfl4qJnXOv3DurRcnPbke2PQj2sc3dFQbsgeAawxU0OB32Iex431JNchtNjMoT ZYdg/avyDDm6w== From: SJ Park To: Cc: SJ Park , Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH 5/9] mm/damon/core: document damon_call()/damon_start() race hang issue Date: Sat, 12 Sep 2026 13:08:06 -0700 Message-ID: <20260912200814.145612-6-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260912200814.145612-1-sj@kernel.org> References: <20260912200814.145612-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: EF91BA0005 X-Stat-Signature: rrmy4b9trkkqs4ubg6zsejphayuhqbhz X-Rspam-User: X-HE-Tag: 1789243704-965760 X-HE-Meta: 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 UED5Rdn0 QsS7KIi+nO9Mzpv36nG7/ozphdkiMcLiyMUOpKem/2O+b7/dRrDM/xTzVp75MEes02Ns0csWd4XCMNGphGoKKAVbkhcAnb5rvl73okyXUPa253qacGoLBdjg4tbAdc4DLB2fjqiNczrkvjcJ0nAbgeEuuoZNGdOyAXxHkSxgo3KvexWNjq1CImsmSJ3XuuTHQNpB800aHMR99Gf84hT/xBaHCOr+OLVwF1/0aoef2dvXQVUUQ8ZYsdKI1cgFOCrgbehitrw3pj8fHZJNxMtUieHLVQQ== 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_obsolte 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 dd27068cb83e3..080355b1f2d9f 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2251,6 +2251,9 @@ 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