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AJvYcCUZq6ttpstdJRPVE0Wk+RXifSOBWNE/RbYt+l2++mylM+qCevR5oSkve17x9k5fdKnK8ade5URZSw==@kvack.org X-Gm-Message-State: AOJu0YxkwKqR/7GgQwW9PV0pvtjvkzslz6TfZoCEnB4L8Rvq2jnGramm BW7JE4PDeqPs6cjhoPf86cRfXz95atck8FRZxsLYOgiLHiVyDfRgYn4TpWpJFCl81oGqTER3LCA 5IyYxUN1T1/Mq/FApMzAthlQcMZmoHKU= X-Gm-Gg: AY/fxX5jLWxh2iKc8PcVktTo7dNrq6goWbMIViTyVHlqAYRSSmoLWu0kGdMUv/qXYGx 8v6GF7/60Gql/TrKaDgc5PKLS3LHPH82DZkxJbgpuevaf3AXVc0AiFvvZ0XZoW9q5pBB5mncKcZ VnwiTvt+wrDTNStR6TPmtS+FlHh6ZEXeh13wx6XVuXvrp/Zh8ozxu10y54dVU7Nt2LSGaP40160 MCwuZqG2Rs9G1OgRzOc3uGh5uUpkRyFMoief3Qb7Vpg5RmbObCtuFQ0wF515vvRs0BuYoCFckkz JNqROKEDtNdYZL0+6+MMPD2eCCXl X-Google-Smtp-Source: AGHT+IEuDSk+uHO37kfw+1KlRWo86Tj0U4wD3OG+qF+cUYxLCnvs8i0ykjdYVfeOvoUjITKDQXbaPZgs6cojh2n4umM= X-Received: by 2002:a05:6000:240c:b0:431:7a0:dbc3 with SMTP id ffacd0b85a97d-432bc9efea0mr4747718f8f.29.1767712440581; Tue, 06 Jan 2026 07:14:00 -0800 (PST) MIME-Version: 1.0 References: <20251223044156.208250-1-roman.gushchin@linux.dev> <20251223044156.208250-4-roman.gushchin@linux.dev> <7ia4ms2zwuqb.fsf@castle.c.googlers.com> In-Reply-To: From: Kumar Kartikeya Dwivedi Date: Tue, 6 Jan 2026 16:13:24 +0100 X-Gm-Features: AQt7F2rALTpWBryWGjQiLYrXRReZq_KM9PVniA_IEDb7aQ0ryO8-rDy8cUAcUVE Message-ID: Subject: Re: [PATCH bpf-next v4 3/6] mm: introduce bpf_get_root_mem_cgroup() BPF kfunc To: Matt Bobrowski Cc: Alexei Starovoitov , Tejun Heo , Roman Gushchin , bpf , linux-mm , LKML , JP Kobryn , Alexei Starovoitov , Daniel Borkmann , Shakeel Butt , Michal Hocko , Johannes Weiner Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 47CEA120012 X-Stat-Signature: 3qw1cifi8h7y6rn7en7skzyoereuonfm X-Rspam-User: X-HE-Tag: 1767712442-626825 X-HE-Meta: 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 zjLhYQ6j 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 5 Jan 2026 at 22:04, Matt Bobrowski wrot= e: > > On Mon, Jan 05, 2026 at 08:05:54AM -0800, Alexei Starovoitov wrote: > > On Sun, Jan 4, 2026 at 11:49=E2=80=AFPM Matt Bobrowski wrote: > > > > > > > > > > > No need for a new KF flag. Any struct returned by kfunc should be > > > > trusted or trusted_or_null if KF_RET_NULL was specified. > > > > I don't remember off the top of my head, but this behavior > > > > is already implemented or we discussed making it this way. > > > > > > Hm, I do not see any evidence of this kind of semantic currently > > > implemented, so perhaps it was only discussed at some point. Would yo= u > > > like me to put forward a patch that introduces this kind of implicit > > > trust semantic for BPF kfuncs returning pointer to struct types? > > > > Hmm. What about these: > > BTF_ID_FLAGS(func, scx_bpf_cpu_rq) > > BTF_ID_FLAGS(func, scx_bpf_locked_rq, KF_RET_NULL) > > BTF_ID_FLAGS(func, scx_bpf_cpu_curr, KF_RET_NULL | KF_RCU_PROTECTED) > > > > I thought they're returning a trusted pointer without acquiring it. > > iirc the last one returns trusted in RCU CS, > > but the first two return just a legacy ptr_to_btf_id ? > > This is something to fix asap then. > > No, AFAIU they do not. These simply return a regular pointer to BTF ID > (PTR_TO_BTF_ID), rather than a formally "trusted" pointer (which would > carry the PTR_TRUSTED flag or a ref_obj_id). scx_bpf_cpu_curr returns > a MEM_RCU pointer (via KF_RCU_PROTECTED), which is somewhat considered > to be trusted within a RCU read-side critical section *ONLY*. > > Kumar/Tejun, Yeah, they don't return a trusted pointer. I think it would make sense to change the behavior here by default. A non-trusted pointer cannot be passed to kfuncs taking trusted arguments, so hopefully it will only make things more permissive and doesn't break anything. > > Please keep me honest here.