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imf18.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=T0IlKExM; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf18.hostedemail.com: domain of sj@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=sj@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1780966486; b=fCWqDST2VPEPaNpgLVIPMDsmOEWP8YDiS//ZwHDcaNSpHE5j1ACh5rdcZ/WSptvs5SSq/z zAS4j2fUKRhW3YRHtfzGtTyGaxS5nbLvNGfZ6zEg9sasAgf6KVRjeQpU/12NtnDeTc1Kc1 0EPzEgMOzb9sG0LXSha9WZsJ50RzNFg= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 1339C601E1; Tue, 9 Jun 2026 00:54:46 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 814E71F00899; Tue, 9 Jun 2026 00:54:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780966485; bh=Jo6v5LwZ9ZiVMHZVW1HuuvAQB6tY4B2I58Ij6xQSkaM=; h=From:To:Cc:Subject:Date; b=T0IlKExMhP67Am9Ab1dPAxhi38p2Vua+v4TKu3QPQfHGzA8IHzar1Y5jk2fDSmNtM PvUclIhidEI+NxyHipSY/tYmzKtQGSKF+tzkba2pJiMUuS3eMGgXUmOoOEft3SbcnC 6PohtZry+ysT3rdCbEkCM6yrvWoQmnBcgnDaqV5zAyLjuiROanwrZ0mQqVQRtY5aEt lohzX6dcvd4nS63QrGw5NSGpNxRIaAhy71vASE2ytg2dzMY4R7wze4bPcmN9B7HvYV Ibvym0crZS2p+N8yfedo7ztg1rafTOGRRWI03QRSu+hrODc96ovoRj0PttrXOcM26M SarjuB4DjXbyQ== From: SeongJae Park To: Cc: SeongJae Park , "# 6 . 16 . x" , Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH] samples/damon/mtier: handle damon_start() failure Date: Mon, 8 Jun 2026 17:54:41 -0700 Message-ID: <20260609005443.2122-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: ACDDE1C0009 X-Stat-Signature: f9ynipfnkmm4y1wh8ddg51hmrmop4agd X-Rspam-User: X-HE-Tag: 1780966486-570688 X-HE-Meta: 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 BrUGYEIL RDbK+jMVqMNlkMgvbc5Drp41Lk4rE1g1Mu1y8eg+WL1816xtAxmH4bGaj+gfZIDsFDSfV0C+yAxQwAh6ex/nFtQNju1zSnkbEtJm76nbUR+U0u/UQrDfPY50J+kDs7hBn5/hIAbwQMR0CgoJT6gOQ/tzsVVrgCxoHhc8KLCLuCT5nhmVPLETuBIwz0hk/4ItCfUl8sR85yYAPSvazgcsBsX9vcypY9TesaYF1hCPKGxt4Nm87X3qeunh/nZwtKIiD1AgqZ8aFkhiSoPVSgl45/PROgQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: damon_sample_mtier_start() callers assume it will clean up resources when it fails. And the function does the cleanup for context buildup failures. However, it is not doing the cleanup for damon_start() failure. As a result, when damon_start() fails, it could leak the memory for DAMON context. Also, if damon_start() fails for only the second context, the first context will indefinitely run, and avoid starting other DAMON contexts since it is running in the exclusive mode. Stop possibly started DAMON context and free the contexts in case of the failure to fix the issues. Note that the issue can reliably be reproduced because the module calls damon_start() in the exclusive mode. For example, $ sudo damo start $ echo Y | sudo tee /sys/module/damon_sample_mtier/parameters/enabled $ sudo cat /proc/allocinfo | grep damon_new_ctx Because the first command is running another DAMON instance, the second command fails the damon_start() call because the new DAMON instance cannot exclusively run. And without this fix, by repeating the second and the third commands above, we can show the memory consumption is only increasing due to the leaks. It requires the sudo permission though. The issue was discovered [1] by Sashiko. [1] https://lore.kernel.org/20260608112455.274231F00893@smtp.kernel.org Fixes: 82a08bde3cf7 ("samples/damon: implement a DAMON module for memory tiering") Cc: # 6.16.x Signed-off-by: SeongJae Park --- samples/damon/mtier.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/samples/damon/mtier.c b/samples/damon/mtier.c index eb1143de8df17..66b591f2180fa 100644 --- a/samples/damon/mtier.c +++ b/samples/damon/mtier.c @@ -174,6 +174,7 @@ static struct damon_ctx *damon_sample_mtier_build_ctx(bool promote) static int damon_sample_mtier_start(void) { struct damon_ctx *ctx; + int err; ctx = damon_sample_mtier_build_ctx(true); if (!ctx) @@ -185,7 +186,15 @@ static int damon_sample_mtier_start(void) return -ENOMEM; } ctxs[1] = ctx; - return damon_start(ctxs, 2, true); + err = damon_start(ctxs, 2, true); + if (!err) + return 0; + + if (damon_is_running(ctxs[0])) + damon_stop(ctxs, 1); + damon_destroy_ctx(ctxs[0]); + damon_destroy_ctx(ctxs[1]); + return err; } static void damon_sample_mtier_stop(void) base-commit: 947b8ee1c1735e548454493da9999a2647621bb0 -- 2.47.3