netdev - Re: [PATCH v3 bpf-next] bpf: make verifier log more relevant by default

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Message-ID: <20201105170202.5bb47fef@redhat.com>
Date:   Thu, 5 Nov 2020 17:02:02 +0100
From:   Jiri Benc <jbenc@...hat.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>, <ast@...com>,
        <daniel@...earbox.net>, <andrii.nakryiko@...il.com>,
        <kernel-team@...com>
Subject: Re: [PATCH v3 bpf-next] bpf: make verifier log more relevant by
 default

On Thu, 23 Apr 2020 12:58:50 -0700, Andrii Nakryiko wrote:
> To make BPF verifier verbose log more releavant and easier to use to debug
> verification failures, "pop" parts of log that were successfully verified.
> This has effect of leaving only verifier logs that correspond to code branches
> that lead to verification failure, which in practice should result in much
> shorter and more relevant verifier log dumps. This behavior is made the
> default behavior and can be overriden to do exhaustive logging by specifying
> BPF_LOG_LEVEL2 log level.

This patch broke the test_offload.py selftest:

[...]
Test TC offloads work...
FAIL: Missing or incorrect message from netdevsim in verifier log
[...]

The selftest expects to receive "[netdevsim] Hello from netdevsim!" in
the log (coming from nsim_bpf_verify_insn) but that part of the log is
cleared by bpf_vlog_reset added by this patch.

How can this be fixed? The log level 1 comes from the "verbose" keyword
passed to tc, I don't think it should be increased to 2.

On a related note, the selftest had to start failing after this commit.
It's a bit surprising it did not get caught, is there a bug somewhere
in the test matrix?

Thanks,

 Jiri