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 6264E2F4A18; Sat, 28 Mar 2026 13:42:57 +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=1774705377; cv=none; b=ncPxxMK3wmy4wZE/8b7EMRrF+vZPq539uKUv+tGkbamcid+FGqwelGK+run970sYNMMvYTZ/nIraNXm3UI27pT+AS7uM/1+LfpDTB/ikfRiIk0b2od/y4DUjb/vRdR7hXi98IQGZ+IhJ7DaKGJjKFa3n+bLDPWtj53grY2mAp68= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774705377; c=relaxed/simple; bh=Zo0xwBlS33TnuFJgADBysYFie+bkoCRf9H3CXGjWLKA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Al8PR3NyzSf+2Vv8jxw0MKbeq8/5qiSmyeR9HXPB7FjXm9UzNiG+ZpG+WweljeQjYWN/nLnE00rgNXFMckaiQMT6AOhcpO5e4PNDzOswoyKD3StXKpnaYIw27oBrUEFo2rG4ksL6ORS6N9wZQ77y+7BrdKZfBv1m5ZvfxYmdQFQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=qu56AoyU; 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="qu56AoyU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F2B8FC4CEF7; Sat, 28 Mar 2026 13:42:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774705377; bh=Zo0xwBlS33TnuFJgADBysYFie+bkoCRf9H3CXGjWLKA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=qu56AoyUrs0g1RWp65nRpAVjFwcSwH649dYJA4JKVdNyldJkRP7P9ZPOZXs1O9Yat rNQ/TDkHGI1Ts9t3nW9tlhLlAFsnnzjFXsYMzXHiUfpbec+mn6PbCFjaRWwXvRZn+P 3XrIPDhDIbRkeGPoJgAimGrZ39in7mXCp07X/2hPr7MqT3r5kx5YC63ThL7mhoGAxp /KF436VCamFOd8N8t1M7OXNZW/EAcAbJypBaxrvUqU0nUelUhPenDU8vwRwmCCRJcp ggXEqXpq2BwQEJIS+DNK9bUkIBs8ZS26EjzHcgCIbeaAZ3R5kIRswiXEakZ1EM/QOb 7vmamGwjOjLmA== 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: Sat, 28 Mar 2026 06:42:55 -0700 Message-ID: <20260328134255.9884-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260328023020.8525-1-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 On Fri, 27 Mar 2026 19:30:20 -0700 SeongJae Park wrote: > 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. Good catch, I will fix this in the next spin. > > > + 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. To my understanding, mult_frac() doesn't do such bypass. Correct me if I'm wrong. > 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. So this concern from sashiko is wrong. Thanks, SJ [...]