From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 EA3D333F378; Sat, 28 Mar 2026 02:30:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774665023; cv=none; b=Hkf/Ofl9fIvKskbEzUIKatT/IKgKwQNM4AHkJoOmHXSi8qP/94OMOspOoMRkFHgawUPr7ggRhGl7+6Or/cxBqdN3BC1Z+2zcxPa8j+uTkI9HsKwr4EDOMQFYA3i/b3+XApBVEvLwLg7q8gKvkljmOUybPBLNzo8P4V6qPkGNQYw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774665023; c=relaxed/simple; bh=LxFmMpfJcOxqkaYRp86376K9yg/HLYeOtxNghx/brdE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=NN7982v3Kr1m/cU4iBQ2xGNNQ2vjKWJ7Cot+xN/a/GlJPQMnGnHSdWfkio1nNaYNDoNCS1Zc9CKQOt6uoLh3dY3azA03zJGL7Cl/B1VOb/2C7CgeOXnM1eNcm2Jw6DqcE/iqLEe9YZUAC0mLKFnBAbO9U+Jzacmc7knR9G15rgk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=di8marH8; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="di8marH8" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 766D8C19423; Sat, 28 Mar 2026 02:30:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774665022; bh=LxFmMpfJcOxqkaYRp86376K9yg/HLYeOtxNghx/brdE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=di8marH8r/JOmw/1cHmnyV1x1x3milaQg7+Hp73F+lCh7c24s5QgzJYd1sweKw4D7 IYX0eHDeVIzE4/1I9QhOsgifEzaqXeR82mWrrcoblYCOiSJ6Ycakdd3ywKWkyFVMm+ xb0mMZ/HcI2haDXc1ZDixf1zXjuw2IVc8FC1XfT1eg9qhtMU20OV2dvN1W8ysvZWEl QBwPm6VmPbLrclwlQBzWsDxLKDCfV2qwV1ipUO7nhWHpXrVJHgIjFtux2hFc8z/oo4 GdmP6IYkvlm6Ihh1xyd/LQgpVaDUA7w/mdEt3tEIt18rGYuduGv8jTMi/ruajNT8I1 m0Kl1/vtLhWjg== From: SeongJae Park To: SeongJae Park Cc: "# 6 . 19 . x" , Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: (sashiko review) [RFC PATCH 2/2] mm/damon/core: validate damos_quota_goal->nid for node_memcg_{used,free}_bp Date: Fri, 27 Mar 2026 19:30:20 -0700 Message-ID: <20260328023020.8525-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260328005412.7606-3-sj@kernel.org> References: Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Forwarding Sashiko review for doing discussions via mails. # review url: https://sashiko.dev/#/patchset/20260328005412.7606-3-sj@kernel.org # start of sashiko.dev inline review commit d10719045bbbd92307cf40ef0886ce0e81cb9caa Author: SeongJae Park mm/damon/core: validate damos_quota_goal->nid for node_memcg_{used,free}_bp This commit adds validation for the damos_quota_goal->nid when calculating node memory cgroup usage ratios. If an invalid node ID is provided, it returns 0% for used memory and 100% for free memory to prevent out-of-bounds memory access during NODE_DATA() lookups. > diff --git a/mm/damon/core.c b/mm/damon/core.c > --- a/mm/damon/core.c > +++ b/mm/damon/core.c > @@ -2273,6 +2273,13 @@ static unsigned long damos_get_node_memcg_used_bp( > unsigned long used_pages, numerator; > struct sysinfo i; > > + if (invalid_mem_node(goal->nid)) { > + if (goal->metric == DAMOS_QUOTA_NODE_MEMCG_USED_BP) > + return 0; > + else /* DAMOS_QUOTA_NODE_MEM_FREE_BP */ This isn't a bug, but there is a typo in the comment here. It says DAMOS_QUOTA_NODE_MEM_FREE_BP instead of DAMOS_QUOTA_NODE_MEMCG_FREE_BP. > + return 10000; > + } > + [ ... ] > si_meminfo_node(&i, goal->nid); > if (goal->metric == DAMOS_QUOTA_NODE_MEMCG_USED_BP) > numerator = used_pages; > else /* DAMOS_QUOTA_NODE_MEMCG_FREE_BP */ > numerator = i.totalram - used_pages; > return mult_frac(numerator, 10000, i.totalram); > } Does this code safely handle nodes with zero managed pages? While the new invalid_mem_node() check ensures the node has N_MEMORY set, a node could still have zero managed pages if all its memory is reserved, or if a concurrent hot-remove event drops the pages to zero just before si_meminfo_node() runs. If i.totalram evaluates to 0, mult_frac() will cause a divide-by-zero kernel panic. Can this calculation also silently overflow on 32-bit architectures? Both used_pages and i.totalram are unsigned long. Since numerator <= i.totalram, mult_frac() bypasses the initial integer division and computes numerator * 10000 directly. If the memory cgroup uses more than ~1.7GB (about 429,496 4KB pages), numerator * 10000 will exceed the maximum 32-bit unsigned long value, resulting in an incorrect ratio. # end of sashiko.dev inline review # review url: https://sashiko.dev/#/patchset/20260328005412.7606-3-sj@kernel.org # # hkml [1] generated a draft of this mail. It can be regenerated # using below command: # # hkml patch sashiko_dev --for_forwarding \ # 20260328005412.7606-3-sj@kernel.org # # [1] https://github.com/sjp38/hackermail Sent using hkml (https://github.com/sjp38/hackermail)