From: Yonghong Song <yonghong.song@linux.dev>
To: bot+bpf-ci@kernel.org, bpf@vger.kernel.org
Cc: ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net,
eddyz87@gmail.com, kernel-team@fb.com, martin.lau@kernel.org,
mason@kernel.org, ihor.solodrai@linux.dev
Subject: Re: [PATCH bpf-next v2 06/20] bpf: Explore the landing pads no call site reaches
Date: Sat, 19 Sep 2026 12:32:53 -0700 [thread overview]
Message-ID: <1dfb59b4-9c23-45f7-8fac-ade2cedb3685@linux.dev> (raw)
In-Reply-To: <ef212951f3582678f582cf9d5664dcbd95377640aaf27eebdc53c86df81a7176@mail.kernel.org>
On 9/17/26 10:44 PM, bot+bpf-ci@kernel.org wrote:
>> commit c93117f24a1a9cc39bfeaef79c42dbff02d8c455
>> Author: Yonghong Song <yonghong.song@linux.dev>
>>
>> bpf: Explore the landing pads no call site reaches
>>
>> A cleanup record need not cover a call an exception can unwind out of: a
>> frontend is free to emit a region around a helper or an ordinary kfunc,
>> both nounwind here. Nothing marks a call site then, and that record's
>> landing pad is reached by nothing at all -- leaving bpf_check_cfg() to
>> refuse the program over code its own frontend had no way not to emit:
>>
>> 0: call bpf_preempt_disable
>> 1: call bpf_preempt_enable record = { begin = 1, end = 2, pad = 4 }
>> 2: r0 = 0
>> 3: exit
>> 4: r1 = pads_ran ll landing pad
>> 6: r2 = *(u64 *)(r1 + 0)
>> 7: r2 |= RAN_NOUNWIND_REC
>> 8: *(u64 *)(r1 + 0) = r2
>> 9: call bpf_unwind_resume
>> 10: exit
>>
>> The range [1,2) holds one call, and it is a kfunc, so an exception cannot
>> come out of it. cleanup_mark_call_sites() marks nothing, nothing pushes an
>> edge to 4, and 4 through 10 are reachable from nothing: "unreachable insn
>> 4". The pad is dead, which is correct -- no exception can ever arrive at it
>> -- but the program is fine and has to load.
>>
>> Walk every pad the table names that the edges did not reach, the way the
>> walk is already re-seeded at an exception callback. From there the pad is
>> code like any other: do_check() never enters it, because no call site
>> dispatches to it, so the dead code sweep removes it along with everything
>> else that was not reached.
>>
>> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
> This looks like a bug fix for the earlier commit that made exception landing
> pads reachable in the CFG. Should this include:
>
> Fixes: a67011bbbca1ba95 ("bpf: Make exception landing pads reachable in the CFG")
No need for this Fixes tag.
>
>
> ---
> AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
> See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
>
> CI run summary: https://github.com/kernel-patches/bpf/actions/runs/35308528711
next prev parent reply other threads:[~2026-09-19 19:33 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-18 4:41 [PATCH bpf-next v2 00/20] bpf: Run exception cleanup landing pads when bpf_throw() unwinds Yonghong Song
2026-09-18 4:42 ` [PATCH bpf-next v2 01/20] bpf: Accept the compiler's exception cleanup table at program load Yonghong Song
2026-09-18 4:42 ` [PATCH bpf-next v2 02/20] bpf: Add the bpf_unwind_resume() kfunc Yonghong Song
2026-09-18 4:42 ` [PATCH bpf-next v2 03/20] bpf: Add lookups for exception cleanup resumes and landing pads Yonghong Song
2026-09-18 5:44 ` bot+bpf-ci
2026-09-19 4:55 ` Alexei Starovoitov
2026-09-19 17:42 ` Yonghong Song
2026-09-18 4:42 ` [PATCH bpf-next v2 04/20] bpf: Mark the call sites an exception cleanup table covers Yonghong Song
2026-09-18 4:42 ` [PATCH bpf-next v2 05/20] bpf: Make exception landing pads reachable in the CFG Yonghong Song
2026-09-18 4:59 ` sashiko-bot
2026-09-19 19:17 ` Yonghong Song
2026-09-18 5:44 ` bot+bpf-ci
2026-09-19 19:32 ` Yonghong Song
2026-09-18 4:42 ` [PATCH bpf-next v2 06/20] bpf: Explore the landing pads no call site reaches Yonghong Song
2026-09-18 5:44 ` bot+bpf-ci
2026-09-19 19:32 ` Yonghong Song [this message]
2026-09-18 4:42 ` [PATCH bpf-next v2 07/20] bpf: Refuse exception cleanup shapes bpf_throw() cannot dispatch Yonghong Song
2026-09-18 4:42 ` [PATCH bpf-next v2 08/20] bpf: Walk the exception unwind in the verifier Yonghong Song
2026-09-18 4:42 ` [PATCH bpf-next v2 09/20] bpf: Refuse a private stack for a program with an exception cleanup table Yonghong Song
2026-09-18 5:44 ` bot+bpf-ci
2026-09-19 19:37 ` Yonghong Song
2026-09-18 4:42 ` [PATCH bpf-next v2 10/20] bpf: Dispatch exception cleanup pads from bpf_throw() Yonghong Song
2026-09-18 5:58 ` bot+bpf-ci
2026-09-19 19:54 ` Yonghong Song
2026-09-18 4:42 ` [PATCH bpf-next v2 11/20] bpf, x86: Dispatch exception cleanup pads at run time Yonghong Song
2026-09-18 5:03 ` sashiko-bot
2026-09-19 20:00 ` Yonghong Song
2026-09-18 5:44 ` bot+bpf-ci
2026-09-19 20:04 ` Yonghong Song
2026-09-18 4:43 ` [PATCH bpf-next v2 12/20] bpf, arm64: " Yonghong Song
2026-09-18 5:44 ` bot+bpf-ci
2026-09-19 20:07 ` Yonghong Song
2026-09-18 4:43 ` [PATCH bpf-next v2 13/20] libbpf: Resolve the compiler's _Unwind_Resume to the kernel's kfunc Yonghong Song
2026-09-18 4:43 ` [PATCH bpf-next v2 14/20] libbpf: Add cleanup_info to bpf_prog_load_opts Yonghong Song
2026-09-18 4:57 ` sashiko-bot
2026-09-19 20:18 ` Yonghong Song
2026-09-18 4:43 ` [PATCH bpf-next v2 15/20] libbpf: Collect .bpf_cleanup records and pass them to the kernel Yonghong Song
2026-09-18 5:00 ` sashiko-bot
2026-09-19 20:21 ` Yonghong Song
2026-09-18 4:43 ` [PATCH bpf-next v2 16/20] libbpf: Carry the exception cleanup table through the light skeleton Yonghong Song
2026-09-18 5:02 ` sashiko-bot
2026-09-19 20:27 ` Yonghong Song
2026-09-18 4:43 ` [PATCH bpf-next v2 17/20] libbpf: Let the static linker carry .bpf_cleanup relocations Yonghong Song
2026-09-18 5:01 ` sashiko-bot
2026-09-19 20:31 ` Yonghong Song
2026-09-18 5:44 ` bot+bpf-ci
2026-09-19 20:32 ` Yonghong Song
2026-09-18 4:43 ` [PATCH bpf-next v2 18/20] selftests/bpf: Add an end-to-end .bpf_cleanup exception test Yonghong Song
2026-09-18 4:59 ` sashiko-bot
2026-09-18 5:58 ` bot+bpf-ci
2026-09-19 20:34 ` Yonghong Song
2026-09-18 4:43 ` [PATCH bpf-next v2 19/20] selftests/bpf: Cover the exception cleanup shapes the chain does not reach Yonghong Song
2026-09-18 5:01 ` sashiko-bot
2026-09-18 5:44 ` bot+bpf-ci
2026-09-19 21:13 ` Yonghong Song
2026-09-18 4:43 ` [PATCH bpf-next v2 20/20] selftests/bpf: Load an exception cleanup program from a light skeleton Yonghong Song
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