Re: [PATCH bpf-next 02/17] bpf: allow RCU-protected lookups to happen from bh context

XDP programs are called from a NAPI poll context, which means the RCU
reference liveness is ensured by local_bh_disable(). Add
rcu_read_lock_bh_held() as a condition to the RCU checks for map lookups so
lockdep understands that the dereferences are safe from inside *either* an
rcu_read_lock() section *or* a local_bh_disable() section. This is done in
preparation for removing the redundant rcu_read_lock()s from the drivers.

Signed-off-by: Toke Høiland-Jørgensen <redacted>
---
 kernel/bpf/hashtab.c  | 21 ++++++++++++++-------
 kernel/bpf/helpers.c  |  6 +++---
 kernel/bpf/lpm_trie.c |  6 ++++--
 3 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 6f6681b07364..72c58cc516a3 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c

@@ -596,7 +596,8 @@ static void *__htab_map_lookup_elem(struct bpf_map *map, void *key)
        struct htab_elem *l;
        u32 hash, key_size;

-       WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held());
+       WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
+                    !rcu_read_lock_bh_held());