From: "Alexei Starovoitov" <alexei.starovoitov@gmail.com>
To: "Mike Bazov" <mikeba@sentinelone.com>
Cc: "Daniel Borkmann" <daniel@iogearbox.net>,
"Andrii Nakryiko" <andrii@kernel.org>,
"Martin KaFai Lau" <martin.lau@linux.dev>,
"Eduard Zingerman" <eddyz87@gmail.com>,
"Kumar Kartikeya Dwivedi" <memxor@gmail.com>,
"Song Liu" <song@kernel.org>,
"Yonghong Song" <yonghong.song@linux.dev>,
"Jiri Olsa" <jolsa@kernel.org>,
"John Fastabend" <john.fastabend@gmail.com>,
"Shuah Khan" <shuah@kernel.org>, <bpf@vger.kernel.org>,
<linux-kselftest@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [EXT.MSG] Re: [PATCH RFC bpf-next 0/2] bpf: Do not let preemption cause false recursion drops in trampoline progs
Date: Tue, 03 Nov 2026 01:49:12 +0000 [thread overview]
Message-ID: <DML75890DWIX.EYB690LPBM1O@gmail.com> (raw)
In-Reply-To: <CAPnbwjrB_je6jXt3BGD-1q1yFs_wFd-Yh9KzixKzLK_X3Stuag@mail.gmail.com>
On Mon, Nov 02, 2026 at 03:24 PM Mike Bazov <mikeba@sentinelone.com> 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.
next prev parent reply other threads:[~2026-11-03 1:49 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-25 11:02 Mike Bazov via B4 Relay
2026-10-25 11:02 ` [PATCH RFC bpf-next 1/2] bpf: Keep recursion-checked trampoline programs non-preemptible on !PREEMPT_RT Mike Bazov via B4 Relay
2026-10-25 11:02 ` [PATCH RFC bpf-next 2/2] selftests/bpf: Add trampoline preemption false-recursion test Mike Bazov via B4 Relay
2026-10-30 22:22 ` [PATCH RFC bpf-next 0/2] bpf: Do not let preemption cause false recursion drops in trampoline progs Alexei Starovoitov
2026-11-02 23:24 ` [EXT.MSG] " Mike Bazov
2026-11-03 1:49 ` Alexei Starovoitov [this message]
2026-11-03 21:28 ` Mike Bazov
2026-11-03 23:46 ` JP Kobryn
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