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Wed, 15 Oct 2025 23:39:56 -0700 (PDT) Received: from localhost.localdomain ([2409:891f:1d64:636e:f4f7:9293:7b0c:3078]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-29099b0215esm17555295ad.112.2025.10.15.23.39.51 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Wed, 15 Oct 2025 23:39:55 -0700 (PDT) From: Yafang Shao To: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org Cc: bpf@vger.kernel.org, linux-mm@kvack.org, Yafang Shao , Lorenzo Stoakes Subject: [PATCH bpf-next 1/2] bpf: mark mm->owner as __safe_rcu_or_null Date: Thu, 16 Oct 2025 14:39:28 +0800 Message-Id: <20251016063929.13830-2-laoar.shao@gmail.com> X-Mailer: git-send-email 2.37.1 (Apple Git-137.1) In-Reply-To: <20251016063929.13830-1-laoar.shao@gmail.com> References: <20251016063929.13830-1-laoar.shao@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When CONFIG_MEMCG is enabled, we can access mm->owner under RCU. The owner can be NULL. With this change, BPF helpers can safely access mm->owner to retrieve the associated task from the mm. We can then make policy decision based on the task attribute. The typical use case is as follows, bpf_rcu_read_lock(); // rcu lock must be held for rcu trusted field @owner = @mm->owner; // mm_struct::owner is rcu trusted or null if (!@owner) goto out; /* Do something based on the task attribute */ out: bpf_rcu_read_unlock(); Suggested-by: Andrii Nakryiko Signed-off-by: Yafang Shao Acked-by: Lorenzo Stoakes --- kernel/bpf/verifier.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index c908015b2d34..d0adf5600c4d 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -7054,6 +7054,9 @@ BTF_TYPE_SAFE_RCU(struct cgroup_subsys_state) { /* RCU trusted: these fields are trusted in RCU CS and can be NULL */ BTF_TYPE_SAFE_RCU_OR_NULL(struct mm_struct) { struct file __rcu *exe_file; +#ifdef CONFIG_MEMCG + struct task_struct __rcu *owner; +#endif }; /* skb->sk, req->sk are not RCU protected, but we mark them as such -- 2.47.3