On 10/21/25 02:07, Song Liu wrote:
On Mon, Oct 20, 2025 at 2:31 PM Andrey Grodzovsky
<[email protected]> wrote:
[...]
Song, I identified another issue in pre 6.6 kernel, building
~/linux-6.5/samples/livepatch/livepatch-sample.c as ko,
before insmoding it, bpftrace fentry/fexit fires as expected, after
insmod, while no errors reported on attachments,
the hooks stop firing, both if attaching before insmod and if attaching
after insmod. If i rrmod the ko, existing hooks
resume working.
ubuntu@ip-10-10-115-238:~$ cat /proc/version_signature
Ubuntu 6.5.0-1008.8-aws 6.5.3
Source obtained to build the test module for the AWS kernel from the
related stable branch -
https://urldefense.com/v3/__https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.5.tar.xz__;!!BmdzS3_lV9HdKG8!xLmCb7PCwCj7vM8JjKx_n7ZUVjW0Oj8Ih9T3YqU4I-JoGy7evTsc7U17emt3nnDmdXdchXxcKHi_6mVBt5QbKzj2$
Let me know what you think.
I tested various stable kernels. I got:
With livepatch, fentry and fexit work on 6.3 kernels.
On 6.4 and 6.5 kernels, the combination stops working since this commit:
commit 60c8971899f3b34ad24857913c0784dab08962f0
Author: Florent Revest <[email protected]>
Date: 2 years, 7 months ago
ftrace: Make DIRECT_CALLS work WITH_ARGS and !WITH_REGS
On 6.5 kernels, it got fixed by the following two commits:
commit a8b9cf62ade1bf17261a979fc97e40c2d7842353
Author: Masami Hiramatsu (Google) <[email protected]>
Date: 1 year, 9 months ago
ftrace: Fix DIRECT_CALLS to use SAVE_REGS by default
commit bdbddb109c75365d22ec4826f480c5e75869e1cb
Author: Petr Pavlu <[email protected]>
Date: 1 year, 8 months ago
tracing: Fix HAVE_DYNAMIC_FTRACE_WITH_REGS ifdef
I tried to cherry-pick 60c8971899f3b34ad24857913c0784dab08962f0
and a8b9cf62ade1bf17261a979fc97e40c2d7842353, on top of 6.5.13
kernel. Then, fentry and fexit both work with livepatch.
I see, thanks for testing! Is the reason it breaks so often is because
this combination of having BPF
and llivepatch together on a system with intersection on same functions
as relatively rate event and
so regressions go easily unnoticed ? Isn't there any relevant automated
testing in upstream that checks for
those types of breaks ?
Thanks,
Andrey
Thanks,
Song
