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b=BclJe7UX4PJvoIUgHUpvGBjveSkdKutvAgrqYPN/Da+DQ3gjmhQdO28N4Exh1rYNE Y7O5dHFS4GkWE7k6XZwAFmAUCFwUDHmjhoExMrt52o5JXyZFwMjh/GlAyw6xCAXh++ Yl7dVxasLJhVUOUtKmBOMj5WhTlrgHn4vf+G0k/r6eR49WQnj3+5Rwy7MYbdRqowEm 5ojRUyrGR244pg300rfIhhOk5DxqKPV5ODOnQTCFsp1uBE30TNdS6khe7uEaabloaF cdPaS6d9WFTgVoJNCh9JW2ZSw8K+AHS55ztyf6L39F2ICY52F00l0aeTy8ryGFVo3D SfvjDEz7EbVQQ== From: SeongJae Park To: SeongJae Park Cc: Andrew Morton , "# 6 . 16 . x" , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: (sashiko review) [PATCH 1/2] mm/damon/core: validate damos_quota_goal->nid for node_mem_{used,free}_bp Date: Sun, 29 Mar 2026 08:34:06 -0700 Message-ID: <20260329153407.46989-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260329043902.46163-2-sj@kernel.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 530FF140009 X-Stat-Signature: qdozqx6718do3z4bbjixgxapqrkfted4 X-Rspam-User: X-HE-Tag: 1774798449-494567 X-HE-Meta: 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 lAzQiG5b Pvd2K1xgeb1xcRn0vS9pm65rUIqvkAd0OogVpYiUnFHZwygXxTj2J6W2s1MupwV0s8bJn37OitjMRevBr+5glssTKlL1ebpl3/lwN9YQCEAwMFcZr8D+008wcbx2uCIj9KgsUOakojrATuOgyTp4Va5A6Gaep+z0PriRpL55hugYz34n27QoKEbx3huuj+B52Uz0Brlv9ShyoSGG1s4i0cU+OVUyZ3aT9hQC1F2DdEM9C2Sl9GwX4Adv4Yx+g9IpsV1FnAo0tOAJ3DCzBNknV3JdFwJU9V7VdSnNTL9OzZUYkmS5nYCS0SFSalcQX5NoFs5Ho66JQngZ7GlbBZ34nD9xLdsVVbFGfJ7rG Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Forwarding Sashiko review for doing discussions via mails. # review url: https://sashiko.dev/#/patchset/20260329043902.46163-2-sj@kernel.org # start of sashiko.dev inline review commit 8c40c45c57722526c25cf1114b386d19a693fc2d Author: SeongJae Park mm/damon/core: validate damos_quota_goal->nid for node_mem_{used,free}_bp This commit adds validation for the node ID in damos_quota_goal to prevent out of bounds memory access when calling si_meminfo_node(). If an invalid node ID is given, it defaults to returning 0% for used memory and 100% for free memory. > diff --git a/mm/damon/core.c b/mm/damon/core.c > --- a/mm/damon/core.c > +++ b/mm/damon/core.c [ ... ] > 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); Does this code still risk a divide-by-zero kernel panic if a memory node has zero managed pages? Even with the new invalid_mem_node() check ensuring node_state(nid, N_MEMORY) is true, a memory node can have present physical pages but zero managed pages if all its memory is reserved early in boot (for example, via memblock_reserve for crash kernels or firmware). In this scenario, si_meminfo_node() sets i.totalram to 0. Since the mult_frac() macro directly evaluates division and modulo, passing i.totalram as 0 will cause a hardware divide-by-zero exception. Should there be an explicit check for i.totalram == 0 before calling mult_frac() here and in other similar quota functions like damos_get_node_memcg_used_bp()? # end of sashiko.dev inline review # review url: https://sashiko.dev/#/patchset/20260329043902.46163-2-sj@kernel.org # # hkml [1] generated a draft of this mail. It can be regenerated # using below command: # # hkml patch sashiko_dev --for_forwarding \ # 20260329043902.46163-2-sj@kernel.org # # [1] https://github.com/sjp38/hackermail Sent using hkml (https://github.com/sjp38/hackermail)