From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D83D0C55171 for ; Sun, 2 Aug 2026 16:21:07 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7E9136B008A; Sun, 2 Aug 2026 12:21:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7C0BA6B0092; Sun, 2 Aug 2026 12:21:01 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6D9056B0096; Sun, 2 Aug 2026 12:21:01 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 43B156B008A for ; Sun, 2 Aug 2026 12:21:01 -0400 (EDT) Received: from smtpin16.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 2B1301604FD for ; Sun, 2 Aug 2026 16:20:59 +0000 (UTC) X-FDA: 85056843438.16.1D12761 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf25.hostedemail.com (Postfix) with ESMTP id 8E9EDA0003 for ; Sun, 2 Aug 2026 16:20:57 +0000 (UTC) Authentication-Results: imf25.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=TSq0UYct; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf25.hostedemail.com: domain of sj@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=sj@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1785687657; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=jjY62t0IWaBhzTuKFbAdxLlz/gg8XTsDxaNCLSSWaXE=; b=opuN5XPL5IVpXbuZE4jxYju23ynt7q9fxQmHBBNpq105WTo4/UQQNLxFAtz3TIqMK08Qfs GnlUj+JyKkKpnZNGs9mKX5lsyu2pqFpr2lW48eh3gUgBJs1IhNsEQHTbwlXhGVdd4GxxpP ojDNs3lCLI4E9pWw91wPtCc4sLYTDJk= ARC-Authentication-Results: i=1; imf25.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=TSq0UYct; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf25.hostedemail.com: domain of sj@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=sj@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1785687657; b=rYeoN5tEwroXYw8MuJzuUo+68ycKZqy1eAueX6yfrobsEBsP2QLKorc4zPdb1H2tOrU7TZ /rvwqZ7+Ilccau7FAFKchh3/tveUQ6W39s3y8sPvBfNtMwG2xSXhdPLXfO2xaL3Se8ZBuJ GNLh7oNtX7iJfOMK32A9y30u6uSsocE= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id A76E640DA2; Sun, 2 Aug 2026 16:20:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 533861F00A3D; Sun, 2 Aug 2026 16:20:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785687656; bh=jjY62t0IWaBhzTuKFbAdxLlz/gg8XTsDxaNCLSSWaXE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=TSq0UYct4CsaLWaMcHePVWRxZ9TID5ACYmfWlfMlJRaKzXP6iN+dtu3Ddk8ksPpgF 591qY0pyf6QPHkLh08YiqZb2g9xJMsp199h7NLKnFqIG3nF1z92suMOM39BDiiHqlI 5sok9cvQifjsOQ1QW4EB2MV19BgAjTZlRSBXBDYWuZeChcdTDtWGwm8C5piKuTPs7Q v9vQEymECJvEOs5vCs+mru1znHuFQEZuoGC5RqIVjYrP90EKe1lhXyfRcAdbuDNzXP Wgbh/kRB31e6ECaEL5ckR+pcqgpq+8I4qpEqThvdEjvHV5iPjSPerXuj/wt00X3/ga qj+FLomyNI8pQ== From: SJ Park To: Cc: SJ Park , stable@vger.kernel.org, Andrew Morton , Yunjeong Mun , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH v2 1/2] samples/damon/mtier: error out for zero quota goal target values Date: Sun, 2 Aug 2026 09:20:48 -0700 Message-ID: <20260802162050.89477-2-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260802162050.89477-1-sj@kernel.org> References: <20260802162050.89477-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 8E9EDA0003 X-Rspam-User: X-Stat-Signature: omfkfbnrx6ksy13qoso98z1rhj73zbnb X-HE-Tag: 1785687657-718673 X-HE-Meta: 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 cq1AdWrQ v5GYi4qSF1RFbksCNFzkM4fcXAKb+A6GCw1MvT+wmTp0cn+c/JbZYvClMqUJU6CIsr0kvJtQ8TlDvuyAngGM86aQ45zYMKVGp3+vECw0yfU8Fhw44483lyQ//kvgFiWZfkLuUnQqO89A6qeYwA74PnR0ibIsaIEtzqaWnKTtApk99r3nYWmYx6n1n1UvTXpSQN3WGGynnC7CQpJpOKPk7u2s6VTJXRYCospzaowuA0hxDyTY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: damos_quota_score() can trigger division by zero if the target_value is zero. DAMON_SAMPLE_MTIER lets users set the target_value via node0_mem_{used,free}_bp parameters. It doesn't guard zero value case, though. As a result, users can trigger division by zero. Fix the issue by returning an error when the user tries to start DAMON with zero node0_mem_{used,free}_bp parameter values. DAMON_SAMPLE_MTIER is just a sample module, but the consequence is quite bad. Also the zero node0_mem_free_bp parameter might look like a reasonable setup to some users. Hence, the issue might really happen in the real world. One reliable way to reproduce the issue is like below: # cd /sys/module/damon_sample_mtier/parameters # echo 4096 > node0_start_addr # echo 8192 > node0_end_addr # echo 8192 > node1_start_addr # echo 81920 > node1_end_addr # echo 0 > node0_mem_free_bp # echo Y > enabled # dmesg -w [...] [18792.235916] Oops: divide error: 0000 [#1] SMP NOPTI [...] [18792.242787] RIP: 0010:damos_quota_score+0x6f/0x480 [...] This issue was discovered [1] by Sashiko. [1] https://lore.kernel.org/20260801202657.117135-1-sj@kernel.org Fixes: c5e67d40a102 ("samples/damon/mtier: add parameters for node0 memory usage") Cc: # 6.17.x Signed-off-by: SJ Park --- samples/damon/mtier.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/samples/damon/mtier.c b/samples/damon/mtier.c index ac9c24b92ead8..d1123ebbfab90 100644 --- a/samples/damon/mtier.c +++ b/samples/damon/mtier.c @@ -156,6 +156,9 @@ static struct damon_ctx *damon_sample_mtier_build_ctx(bool promote) if (!scheme) goto free_out; damon_set_schemes(ctx, &scheme, 1); + /* zero target value causes division by zero in damos_quota_store() */ + if (!node0_mem_used_bp || !node0_mem_free_bp) + goto free_out; quota_goal = damos_new_quota_goal( promote ? DAMOS_QUOTA_NODE_MEM_USED_BP : DAMOS_QUOTA_NODE_MEM_FREE_BP, -- 2.47.3