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 18253224B05; Thu, 26 Mar 2026 00:38:53 +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=1774485533; cv=none; b=NhITlZsrBQJ0HIhAUu2LjECTZ1rPGIsAkiT/96X9aT5baUWAaq5VH/h2LcTyyw57K6bc3NRRrSiVuQ/xFTT4AqSNHU433/XQF/HLgkxcTSKBJbr1zbkSwsilksEcluIonPqq9euEk68zoGbtep44eJMz2rsbrrk6+ws++oYR3WY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774485533; c=relaxed/simple; bh=FFUCjB4kqdoVSzQIVahoi0U9tLwThKz0ltut+AgLlCU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=f7DFZQKZsfyLMmlNJ4zSgZsThRpjHHv7ml0xaxQ0xsZ9phM33sq33PiCkCW40dGwXVql7uRCINLfWGjrZdUocw40bhIlNWYyKgTcFdq4BOH4a0wGGllwjpdWkW1i+vBSKHmvOOopkt7gMYqd/5ccNFBUNuDGWBx0GOFT99+baFA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Bh8YUanE; 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="Bh8YUanE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B3133C4CEF7; Thu, 26 Mar 2026 00:38:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774485532; bh=FFUCjB4kqdoVSzQIVahoi0U9tLwThKz0ltut+AgLlCU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Bh8YUanEvEHCeFdyPxQTDjAlpfJiy8k8klzB6eh1WQhmo0J6+5zqrcdTU3+O/z7O6 7TDzgDCXWE2xsdhjLPpVJLEfrb0y3nj4xoTuf/HMS5TfXpUbTQ8hqYqRvnbhyaOvvW 8fqyMtbWm5vpOPSSJyMgnbGSBsDKIWEsJx6KVWipLW2ciGnFAiX7+i0t5uI8eHOELV 9XrgwL0x2sbo16h5+c1rmYhk2Ar1hK36hKgm6b1OmRQQA++BhrcsNKT7SNpFVUahPp rd+N+97jetE6mn5cY1uyqYFkKnSCDPVfSrcFFRDh31hvSS8yBF3GeGS2457HzIHX+l xPr6YhIRr6T6A== From: SeongJae Park To: SeongJae Park Cc: Josh Law , Andrew Morton , damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: (sashiko review) [PATCH v2] mm/damon/core: validate goal nid before accessing node data Date: Wed, 25 Mar 2026 17:38:44 -0700 Message-ID: <20260326003845.77426-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260326001051.76219-1-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 Wed, 25 Mar 2026 17:10:50 -0700 SeongJae Park wrote: > Forwarding Sashiko review for doing discussions via mails. > > # review url: https://sashiko.dev/#/patchset/20260325155221.202700-1-objecting@objecting.org > # start of sashiko.dev inline review > commit 24e25058b8f508495d0b3db33bed16564df7fed4 > Author: Josh Law > Subject: mm/damon/core: validate goal nid before accessing node data > > This patch adds bounds and node_state(N_MEMORY) checks before using > goal->nid from userspace to prevent out-of-bounds access in NODE_DATA(). > > Cc: stable@vger.kernel.org > > > diff --git a/mm/damon/core.c b/mm/damon/core.c > > index db6c67e52d2b..ed45a7443abe 100644 > > --- a/mm/damon/core.c > > +++ b/mm/damon/core.c > > @@ -2245,6 +2245,10 @@ static __kernel_ulong_t damos_get_node_mem_bp( > > struct sysinfo i; > > __kernel_ulong_t numerator; > > > > + if (goal->nid < 0 || goal->nid >= MAX_NUMNODES || > > + !node_state(goal->nid, N_MEMORY)) > > + return 0; > > + > > When goal->nid is invalid or offline, this unconditionally returns 0. > For the DAMOS_QUOTA_NODE_MEM_FREE_BP metric, wouldn't returning 0 imply > 0% free memory? > > Could this cause the DAMON feedback loop to interpret the goal as > severely under-achieved and drastically increase the scheme's > aggressiveness? > > Should this fallback logic check the metric type and return 10000 > (100% free) for FREE_BP metrics to fail gracefully, mirroring the > existing fallback logic used when a memory cgroup lookup fails? I am also thinking similar to sashiko. Could you please make the change? > > > si_meminfo_node(&i, goal->nid); > > if (goal->metric == DAMOS_QUOTA_NODE_MEM_USED_BP) > > numerator = i.totalram - i.freeram; > > else /* DAMOS_QUOTA_NODE_MEM_FREE_BP */ > > numerator = i.freeram; > > return mult_frac(numerator, 10000, i.totalram); > > While not introduced by this patch, since this function is being > modified to handle node edge cases, is it possible for a node to have > N_MEMORY set, but have 0 managed pages? For example, if all of its > memory is reserved for hugetlb or unmanaged ZONE_DEVICE memory. I'm not very sure if this is really possible. Josh, do you know? > > If so, si_meminfo_node() would set i.totalram to 0. Would the call > to mult_frac() then cause a divide-by-zero panic when it evaluates > x_ / d_ ? If sashiko's theory is true, I think we should add a zero value check here? > > > @@ -2261,6 +2265,10 @@ static unsigned long damos_get_node_memcg_used_bp( > > unsigned long used_pages, numerator; > > struct sysinfo i; > > > > + if (goal->nid < 0 || goal->nid >= MAX_NUMNODES || > > + !node_state(goal->nid, N_MEMORY)) > > + return 0; > > + > > Similar to the function above, returning 0 unconditionally here for > DAMOS_QUOTA_NODE_MEMCG_FREE_BP might artificially trigger maximum > reclaim aggressiveness. Similar to my above comment, I agree to sashiko. Thanks, SJ [...]