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b=YhO2hofa6+3lYiZaEde0HHBPhe9ZGHPsQ2LSq1Kn3ukb2SYQeegyR5A9GjBjd7fKU vpre8iK+afxqBfvUW7JEvRnX2gmjkuvP7GEccQFoiE/TF1JBAhx2ZhN9YKNyzOP291 tnUAIF6YwHG2RKzwSBVPdWRmiunsRvKMM7oupl1iJfYVyzlo9E3kfA60D5T7+MQhXK 2HNitmVZNcRcsDwioM062afplwo5NgcQ9IqHbppt24U9TV+ZLratI9Fyz05PNK/SsQ rYq/P7WrHV6WOV/ob8zg383A0oTB75/dUb+/1clv5K9fDWDvDT/Bf1qCRTDQCwCcUo OUkB11T8nA24Q== From: SeongJae Park To: SeongJae Park Cc: "# 6 . 16 . x" , Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: (sashiko review) [RFC PATCH 1/2] mm/damon/core: validate damos_quota_goal->nid for node_mem_{used,free}_bp Date: Sat, 28 Mar 2026 06:32:15 -0700 Message-ID: <20260328133216.9697-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260328022956.8415-1-sj@kernel.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: CCA69C0002 X-Stat-Signature: 46d856xia4ngozzus1uk6y6m516hasia X-HE-Tag: 1774704738-428854 X-HE-Meta: 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 mUf/Kr0k pG4faxkHN/vg8QurTla4/ahvysTSqG14bAhwePPDfEgkh+Bu4/s4EE3cLNHJitS0+YGmfJDtuuYqFZKElh3JsHOcUUWRzgB44IleSIQRbVcssA9ZF9pbpvu+bDz//AD/8Be5VVBocfm8xg7iHFjzWUtGkNT8QgHKbc5eZEzilqooOAWN+wCpHlh0zyQXoPe78HUU93jyCROEDUn0dNVigAI6wtkjLVGj5IM+vBAEQHrooXwVmEKWY6Ss15Hvrd88beN0CQ2hdWSazaTUGKzbfMi/ZSKmZeUw3XM/EmQrSTenoC1UtNdk1rbEfxV/fXovmpmsnWfEDAsgFm94= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: TL;DR: good catch but orthogonal to this patch. On Fri, 27 Mar 2026 19:29:55 -0700 SeongJae Park wrote: > Forwarding Sashiko review for doing discussions via mails. > > # review url: https://sashiko.dev/#/patchset/20260328005412.7606-2-sj@kernel.org > # start of sashiko.dev inline review > commit add63112781ae04626ae6cb9bce55a85234f6e49 > Author: SeongJae Park > > mm/damon/core: validate damos_quota_goal->nid for node_mem_{used,free}_bp > > This commit adds validation for the given memory node id to prevent out of > bounds access when calculating node memory metrics. If an invalid node id > is provided, it defaults to returning 0% used or 100% free memory. > > > diff --git a/mm/damon/core.c b/mm/damon/core.c > > --- a/mm/damon/core.c > > +++ b/mm/damon/core.c > > [ ... ] > > > @@ -2239,12 +2239,24 @@ static inline u64 damos_get_some_mem_psi_total(void) > > static __kernel_ulong_t damos_get_node_mem_bp( > > struct damos_quota_goal *goal) > > { > > struct sysinfo i; > > __kernel_ulong_t numerator; > > > > + if (invalid_mem_node(goal->nid)) { > > + if (goal->metric == DAMOS_QUOTA_NODE_MEM_USED_BP) > > + return 0; > > + else /* DAMOS_QUOTA_NODE_MEM_FREE_BP */ > > + return 10000; > > + } > > + > > 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); > > Could this result in a division by zero panic? > > While invalid_mem_node() checks node_state(nid, N_MEMORY) to ensure the > node has present memory pages, si_meminfo_node() sets i.totalram based > solely on managed pages. If all memory on the node is reserved, i.totalram > could be 0. > > Additionally, since the node_state() check is lockless, memory could be > concurrently offlined after invalid_mem_node() but before si_meminfo_node(), > also resulting in i.totalram being 0. > > Would it be safer to explicitly verify i.totalram is greater than 0 before > calling mult_frac()? I'm not very sure if totalram becoming zero is available, but seems making sense. But orthogonal to this patch. I will work on this with another patch. Thanks, SJ [...]