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AJvYcCVdRk2ao+bj5oqLqKY26uvDFiwJJtY9YqzAYdJnaGZ35yW0V8dbaI6oloPNVHTheMsj2GE=@vger.kernel.org, AJvYcCVlC3MTPjFIc+kEx3xigBcTLglClNtfrRZG1vjAxspeUD9lJQNXTC3U2+zVkV+w2OpOczzgDm5h+Cpd@vger.kernel.org X-Gm-Message-State: AOJu0YxmNQEVzHRQRlQE6bzCAQn8gXogx0P6ujaTjSMwwtMH3NbDCtZM DIbXiJdAbDHsMxSQy0BaY1oc603Gxw6QXZBUKnTjD0urQ/uCh9JMbLlPCn4rDH9vt5UU1xsnL7V XddXK3kZ28dEmSjX0LeP4+igYv0rixAc= X-Gm-Gg: ASbGncvSNuWEiHv9O+67REKy8s2jKj6rcG5mhNZ4Th9jrli45GMqRpHJCBLow5FMm7q YLl0ZuYBqlEuWqKfT504yoQKZbovCdhqrjxku24YS0sKevX2Y+ff2z4wrZwJHrHLStvPWeQI4pn QJTixEP1x272bPzjx1ViiX7j3Uts1aDo7hmvKx/lte7PR2jjgFzPR7OqjtQ7+JyeU7z8000QGAV fbA/7mr6sMhn9mvBF6hqaNptGzbdQXA99SHuTbbv/7btP9RrSs= X-Google-Smtp-Source: AGHT+IFFAjUELcmzEUUIYc8SHA/xvC9uJFbqt/nPTvZ1yb5BBrEZja9lEGaS63h6U3LHxjGEGcjgnnXdq8S/DdNl+yo= X-Received: by 2002:ad4:4e13:0:b0:70d:fd26:f22e with SMTP id 6a1803df08f44-70dfd26fbd6mr27305636d6.15.1756437354406; Thu, 28 Aug 2025 20:15:54 -0700 (PDT) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20250826071948.2618-1-laoar.shao@gmail.com> <20250826071948.2618-4-laoar.shao@gmail.com> <5fb8bd8d-cdd9-42e0-b62d-eb5a517a35c2@lucifer.local> <4ee47412-2a33-431e-b667-2daf25bf0b38@lucifer.local> In-Reply-To: <4ee47412-2a33-431e-b667-2daf25bf0b38@lucifer.local> From: Yafang Shao Date: Fri, 29 Aug 2025 11:15:17 +0800 X-Gm-Features: Ac12FXw78zOh0YCbOC1DZdJk9pXKNjEimCM6h54y2oGXNzxpBZAFFy6hpw6Sz_U Message-ID: Subject: Re: [PATCH v6 mm-new 03/10] mm: thp: add a new kfunc bpf_mm_get_task() To: Lorenzo Stoakes Cc: Andrii Nakryiko , akpm@linux-foundation.org, david@redhat.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, hannes@cmpxchg.org, usamaarif642@gmail.com, gutierrez.asier@huawei-partners.com, willy@infradead.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, ameryhung@gmail.com, rientjes@google.com, corbet@lwn.net, bpf@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, Aug 28, 2025 at 6:51=E2=80=AFPM Lorenzo Stoakes wrote: > > On Wed, Aug 27, 2025 at 02:50:36PM -0700, Andrii Nakryiko wrote: > > On Wed, Aug 27, 2025 at 8:48=E2=80=AFAM Lorenzo Stoakes > > wrote: > > > > > > On Tue, Aug 26, 2025 at 03:19:41PM +0800, Yafang Shao wrote: > > > > We will utilize this new kfunc bpf_mm_get_task() to retrieve the > > > > associated task_struct from the given @mm. The obtained task_struct= must > > > > be released by calling bpf_task_release() as a paired operation. > > > > > > You're basically describing the patch you're not saying why - yeah yo= u're > > > getting a task struct from an mm (only if CONFIG_MEMCG which you don'= t > > > mention here), but not for what purpose you intend to use this? > > > > > > > > > > > Signed-off-by: Yafang Shao > > > > --- > > > > mm/bpf_thp.c | 34 ++++++++++++++++++++++++++++++++++ > > > > 1 file changed, 34 insertions(+) > > > > > > > > diff --git a/mm/bpf_thp.c b/mm/bpf_thp.c > > > > index b757e8f425fd..46b3bc96359e 100644 > > > > --- a/mm/bpf_thp.c > > > > +++ b/mm/bpf_thp.c > > > > @@ -205,11 +205,45 @@ __bpf_kfunc void bpf_put_mem_cgroup(struct me= m_cgroup *memcg) > > > > #endif > > > > } > > > > > > > > +/** > > > > + * bpf_mm_get_task - Get the task struct associated with a mm_stru= ct. > > > > + * @mm: The mm_struct to query > > > > + * > > > > + * The obtained task_struct must be released by calling bpf_task_r= elease(). > > > > > > Hmmm so now bpf programs can cause kernel bugs by keeping a reference= around? > > > > BPF verifier will reject any program that cannot guarantee that > > bpf_task_release() will always be called. So there shouldn't be any > > problem here. > > Ah that's nice! > > What specifically here is enforcing that? Apologies again - BPF is new to= me. The KF_ACQUIRE and KF_RELEASE flags enforce resource management. If a BPF helper function (e.g., bpf_mm_get_task()) is marked with KF_ACQUIRE, the pointer it returns must be released by a corresponding helper marked with KF_RELEASE (e.g., bpf_task_release()). The BPF verifier will reject any program that fails to pair these calls correctly. --=20 Regards Yafang