From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4889D3C3BEF; Sat, 12 Sep 2026 20:08:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789243705; cv=none; b=A0K9hByTqBCsFOxDRD9kBSZodg4pxWI8TTrPYOV0qbIsUGT8qGDlq9uSCFesGserPSo/JsOBDc53P/V6PkPvZqWM3ZpyRAyZbmKXs2c9L7xDbTcX22PAUaLKF5pDTckFPC9OCjB/zSoKp1S8fLd5SRf4YpMXQ7qbUex+N5bYokc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789243705; c=relaxed/simple; bh=xTjfs5kUa7x/iCo3n2Za6YcXKxyTeh0P4akSN9qz+Uc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GFP8h3i0+UdNqqRgppMGcsHl0mvnotvVhkx2YFa+ubD113C1FtHuPpKsYyi7BIuzbEMYjypw0lXQMEfRMGFtJ9db0fG1ZCYPcbjNIIgQUff3rDO8rD3OKsc2MZhSkwBcJI2Y9xhfsGgdolXXB80Gwo/fWQJzbh4iWU7UBZl2v88= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=K51/4QtD; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="K51/4QtD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 07DAD1F000FF; Sat, 12 Sep 2026 20:08:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789243704; bh=80o1zjbsa4JPAD6h+nen9K5vfO8rOszkn9G9ncWmsSc=; h=From:To:Cc:Subject:Date:In-Reply-To:References; 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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