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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1dfb59b4-9c23-45f7-8fac-ade2cedb3685@linux.dev \
--to=yonghong.song@linux.dev \
--cc=andrii@kernel.org \
--cc=ast@kernel.org \
--cc=bot+bpf-ci@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=eddyz87@gmail.com \
--cc=ihor.solodrai@linux.dev \
--cc=kernel-team@fb.com \
--cc=martin.lau@kernel.org \
--cc=mason@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.