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Mon, 26 Oct 2026 11:44:18 -0400 (EDT) Date: Mon, 26 Oct 2026 15:44:17 +0000 From: Kiryl Shutsemau To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Gregory Price , Zi Yan , Joshua Hahn , Rakie Kim , Ying Huang , Johannes Weiner , Vladimir Davydov , Michal Hocko , Hugh Dickins , Baolin Wang , Lukas Czerner , Carlos Maiolino , Christian Brauner , Jan Kara , Daniel Verkamp , Jeff Xu , Muchun Song , Oscar Salvador , David Stevens , "Matthew Wilcox (Oracle)" , William Kucharski , Chris Li , Kairui Song , Nhat Pham , Miaohe Lin , Naoya Horiguchi , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Chris Mason , stable@vger.kernel.org Subject: Re: [PATCH 01/16] mm/mempolicy: charge shared policy nodes Message-ID: References: <20261026-fixes_shmem-v1-0-703206d5fa0c@kernel.org> <20261026-fixes_shmem-v1-1-703206d5fa0c@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261026-fixes_shmem-v1-1-703206d5fa0c@kernel.org> X-Rspamd-Queue-Id: DDC4740008 X-Rspam-User: X-Stat-Signature: 89iyg4x9ri19q4agwzhrnkbhdu574qy3 X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam03 X-HE-Tag: 1793029462-76819 X-HE-Meta: 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 PaXuma0O 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Mon, Oct 26, 2026 at 10:40:34AM +0100, David Hildenbrand (Arm) wrote: > From: Chris Mason > > Any local user can bypass memory.max with mbind() on a tmpfs file, and > allocate unbounded kernel memory. > > mbind() sets a NUMA memory policy for a range of a mapping. If the > mapping is of a shmem and friends, the kernel also stores the policy on > the inode, in a tree with one entry per range of the file. > > Each mbind() on a single page of a mapping can add one shared policy node > (struct sp_node) and one struct mempolicy to that tree. They outlive the > mapping and stay around until the inode is destroyed. The tree is not > bounded by the file size, so the file can be empty. > > Memory that user space can allocate must be charged to a memory cgroup. A > slab cache does that for all of its objects if it is created with > SLAB_ACCOUNT. numa_policy_init() creates the slab caches for both > structs without SLAB_ACCOUNT, so they are not charged to any cgroup. > > Reproduced with mbind() on single pages of an empty tmpfs file, from a > cgroup with memory.max=8M: the global OOM killer killed tasks owned by > root, and the machine panicked. > > Fix this by creating both caches with SLAB_ACCOUNT. This change implies > that mbind() can now fail when running into memcg limits. Further, > the policy_cache also serves task and VMA policies, so they are > similarly accounted now. > > Note that per-file limits are not really helpful, as the user could > simply use many files; having limits per user is tricky as well. > > Fix generated by an LLM and submitted by Chris Mason in private. > > Fixes: 5d097056c9a0 ("kmemcg: account certain kmem allocations to memcg") > Cc: stable@vger.kernel.org > Signed-off-by: Chris Mason > [ david: smaller description tweaks ] > Signed-off-by: David Hildenbrand (Arm) Acked-by: Kiryl Shutsemau (Meta) -- Kiryl Shutsemau / Kirill A. Shutemov