Re: [PATCH bpf-next v4 07/12] bpf: keep module BTF until the vmlinux BTF is available

Module BTF is split BTF against the vmlinux BTF and is parsed in the
module notifier.  With CONFIG_DEBUG_INFO_BTF=m the vmlinux BTF may not be
loaded yet when a module loads, and the notifier cannot load btf_vmlinux
(that would nest a module load in a module load).

So a module loaded before the vmlinux BTF keeps a copy of its .BTF and
.BTF.base and gets a list entry with btf == NULL; its kfunc, dtor kfunc
and struct_ops registrations wait on that entry.  Without a .BTF.base
the data is final and is exposed in /sys/kernel/btf right away (the raw
bytes need no parsing); with one, parsing relocates the data in place,
so its file is created once parsed, as with =y.  The next patch creates
that file earlier.

When the vmlinux BTF arrives, btf_parse_deferred_modules() parses the
kept copies (the copy is the one btf_parse_module() makes anyway, so an
[ ... ]
With =y the BTF is present from boot and the notifier takes the existing
path.  Still nothing is reachable until the Kconfig symbol becomes a
tristate.

Signed-off-by: Jay Wang <redacted>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261001225214.12351-1-wanjay@amazon.com?part=7