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Mon, 02 Nov 2026 17:49:15 -0800 (PST) Received: from localhost ([153.61.198.242]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3ae85e4ff4csm10375603a91.1.2026.11.02.17.49.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Nov 2026 17:49:14 -0800 (PST) Content-Type: text/plain; charset=UTF-8 Date: Tue, 03 Nov 2026 01:49:12 +0000 Message-Id: Cc: "Daniel Borkmann" , "Andrii Nakryiko" , "Martin KaFai Lau" , "Eduard Zingerman" , "Kumar Kartikeya Dwivedi" , "Song Liu" , "Yonghong Song" , "Jiri Olsa" , "John Fastabend" , "Shuah Khan" , , , Subject: Re: [EXT.MSG] Re: [PATCH RFC bpf-next 0/2] bpf: Do not let preemption cause false recursion drops in trampoline progs From: "Alexei Starovoitov" To: "Mike Bazov" In-Reply-To: References: <20261025-b4-bpf-trampoline-preempt-v1-0-198dcdc0c6ac@sentinelone.com> Content-Transfer-Encoding: 8bit X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 On Mon, Nov 02, 2026 at 03:24 PM Mike Bazov wrote: > To fix fentry/fexit while keeping preemption enabled, we'll need to: > 1. Disable private stack for fentry/fexit (so each task uses its own > kernel stack), and Yes. Then the stack limit covers the whole call chain instead of one frame. It's 2 Kbytes on x86-64 and arm64 now. > 2. Check recursion in __bpf_prog_enter_recur() per-task rather than via > the per-CPU prog->active counter (still blocking same-task recursion > and IRQ/NMI re-entry on the same CPU, while allowing a preempting > Task B to run). No. I don't think we can switch to per-task that easily. For your use case try fsession. It was added specifically to match entry/exit.