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