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 BA96D3E5A20; Mon, 3 Aug 2026 13:40:37 +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=1785764438; cv=none; b=hnK3k+tNU2kYPDXCK5DSsyUJAtpvPFv0f6UQOgFZBCQuiseWecfFk1KKsPCfMBereMDakJJ+KHPEhwrpE99+ajRgMGAelp0n2NzZZIuDWut8FRsM1Iwt86PRKHCHwkUBPLzAWBZ2eLizboWrvpaL69NCpSbQw53AevwQScSykjc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785764438; c=relaxed/simple; bh=pT+muvkgd8dj3wxs8gC3+KsYxNu/Gu3J6uacElnJezY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=TAEQavGyR1+Ts8NxI5GkpJPWjtYW+Xr2AWG+bQvfeMMlJfowkvH+G9Hg2p8uWKlbPpZbksLZnXfjKgaqHabTyvYK3MLUdLtPhNTgA5XiS0ig0hnaHDvtbj0XeH6MSPfGIjuvZGhJpMXd1/M6iS9IrtUm2WPYHZyTrjVBKGeWQIg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=aclTRPdn; 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="aclTRPdn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5351C1F00A3D; Mon, 3 Aug 2026 13:40:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785764437; bh=jjY62t0IWaBhzTuKFbAdxLlz/gg8XTsDxaNCLSSWaXE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=aclTRPdnyUUFJAaDIyxB8DfZEf7Ky7QyAimNORLoUdnJ4Oi1/Nm99kcVp7xkdHlvP SgsnW/KyBf463A1xcPkJPZpmB404twh+nsEsMgR9p6mrjbC6pKACgkVr9n3sFnHNSs fHk/mna5e2cimHSzTI8hnpkCAQca0yU/LLkmDRyONCpsTXNRF8mK9WuurQiqnS/XdT TCz+7qyf+PFB9oogPMCcZExR22SwB6X7KKZQhF2/kW70qn1eMgxLqjrJQre2A0leZi DKfAVQfKIXZAooTmU3b8XJogKd22WzKlVqk17UrCDgMrIli/QSMSVJjAgmcZhVUP7K 31o1Kpd3qxFxA== From: SJ Park To: Andrew Morton Cc: SJ Park , stable@vger.kernel.org, Yunjeong Mun , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 1/2] samples/damon/mtier: error out for zero quota goal target values Date: Mon, 3 Aug 2026 06:40:32 -0700 Message-ID: <20260803134034.15217-2-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260803134034.15217-1-sj@kernel.org> References: <20260803134034.15217-1-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 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