netdev - Re: [PATCH bpf-next v8 00/10] Introduce unstable CT lookup helpers

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Message-ID: <20220218222017.czshdolesamkqv4j@apollo.legion>
Date:   Sat, 19 Feb 2022 03:50:17 +0530
From:   Kumar Kartikeya Dwivedi <memxor@...il.com>
To:     Alexander Egorenkov <Alexander.Egorenkov@....com>
Cc:     andrii@...nel.org, ast@...nel.org, bpf@...r.kernel.org,
        brouer@...hat.com, daniel@...earbox.net, fw@...len.de,
        john.fastabend@...il.com, kafai@...com, maximmi@...dia.com,
        netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
        pablo@...filter.org, songliubraving@...com, toke@...hat.com,
        yhs@...com, Ilya Leoshkevich <iii@...ux.ibm.com>
Subject: Re: [PATCH bpf-next v8 00/10] Introduce unstable CT lookup helpers

On Sat, Feb 19, 2022 at 01:49:04AM IST, Alexander Egorenkov wrote:
>
> Hi,
>
> we are having a problem loading nf_conntrack on linux-next:
>
> # modprobe nf_conntrack
> modprobe: ERROR: could not insert 'nf_conntrack': Unknown symbol in module, or unknown parameter (see dmesg)
> modprobe: ERROR: Error running install command '/sbin/modprobe --ignore-install nf_conntrack  && /sbin/sysctl --quiet --pattern 'net[.]netfilter[.]nf_conntrack.*' --system' for module nf_conntrack: retcode 1
> modprobe: ERROR: could not insert 'nf_conntrack': Invalid argument
>
> # dmesg
> [ 3728.188969] missing module BTF, cannot register kfuncs
> [ 3748.208674] missing module BTF, cannot register kfuncs
> [ 3748.567123] missing module BTF, cannot register kfuncs
> [ 3873.597276] missing module BTF, cannot register kfuncs
> [ 3874.017125] missing module BTF, cannot register kfuncs
> [ 3882.637097] missing module BTF, cannot register kfuncs
> [ 3883.507213] missing module BTF, cannot register kfuncs
> [ 3883.876878] missing module BTF, cannot register kfuncs
>
> # zgrep BTF /proc/config.gz
> CONFIG_DEBUG_INFO_BTF=y
> CONFIG_PAHOLE_HAS_SPLIT_BTF=y
> CONFIG_DEBUG_INFO_BTF_MODULES=y
>
> It seems that nf_conntrack.ko is missing a .BTF section
> which is present in debuginfo within
> /usr/lib/debug/lib/modules/*/kernel/net/netfilter/nf_conntrack.ko.debug instead.
>
> Am i correct in assuming that this is not supported (yet) ?
>
> We use pahole 1.22 and build linux-next on Fedora 35 as a set of custom
> packages. Architecture is s390x.
>

+Cc Ilya

Thanks for the report, Alex.

My assumption was that if DEBUG_INFO_BTF options was enabled, and BTF was not
present, it is a problem, but it seems it can happen even when the options are
enabled.

I guess if .BTF section isn't supported/emitted on s390x, we have to relax the
error and print a warning and ignore it, but I am not sure. Ilya would probably
know the current status.

We have already relaxed it once in (bpf-next):

c446fdacb10d ("bpf: fix register_btf_kfunc_id_set for !CONFIG_DEBUG_INFO_BTF")

If this doesn't work on s390x, we should probably just print a warning when
CONFIG_DEBUG_INFO_BTF is enabled and btf == NULL, and return 0.

> Thanks
> Regards
> Alex
>

--
Kartikeya