Re: [PATCH bpf-next v2 4/8] bpf: Add kfunc bpf_rcu_read_lock/unlock()

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

On Tue, Nov 08, 2022 at 01:11:09PM IST, Yonghong Song wrote:
> Add two kfunc's bpf_rcu_read_lock() and bpf_rcu_read_unlock(). These two kfunc's
> can be used for all program types. A new kfunc hook type BTF_KFUNC_HOOK_GENERIC
> is added which corresponds to prog type BPF_PROG_TYPE_UNSPEC, indicating the
> kfunc intends to be used for all prog types.
>
> The kfunc bpf_rcu_read_lock() is tagged with new flag KF_RCU_LOCK and
> bpf_rcu_read_unlock() with new flag KF_RCU_UNLOCK. These two new flags
> are used by the verifier to identify these two helpers.
>
> Signed-off-by: Yonghong Song <yhs@fb.com>
> ---
>  include/linux/bpf.h  |  3 +++
>  include/linux/btf.h  |  2 ++
>  kernel/bpf/btf.c     |  8 ++++++++
>  kernel/bpf/helpers.c | 25 ++++++++++++++++++++++++-
>  4 files changed, 37 insertions(+), 1 deletion(-)
>
> For new kfuncs, I added KF_RCU_LOCK and KF_RCU_UNLOCK flags to
> indicate a helper could be bpf_rcu_read_lock/unlock(). This could
> be a waste for kfunc flag space as the flag is used to identify
> one helper. Alternatively, we might identify kfunc based on
> btf_id. Any suggestions are welcome.
>

It can be done similar to this change:
https://lore.kernel.org/bpf/20221107230950.7117-17-memxor@gmail.com
So compare meta.func_id to special_kfunc_list[KF_bpf_rcu_read_lock].