bpf: no longer acquire map_idr_lock in bpf_map_inc_not_zero()

bpf_sk_storage_clone() is the only caller of bpf_map_inc_not_zero()
and is holding rcu_read_lock().

map_idr_lock does not add any protection, just remove the cost
for passive TCP flows.

Signed-off-by: Eric Dumazet <[email protected]>
Cc: Kui-Feng Lee <[email protected]>
Cc: Martin KaFai Lau <[email protected]>
Acked-by: Stanislav Fomichev <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: edumazet

kernel/bpf/syscall.c

@@ -1593,11 +1593,8 @@ struct bpf_map *__bpf_map_inc_not_zero(struct bpf_map *map, bool uref)
 
 struct bpf_map *bpf_map_inc_not_zero(struct bpf_map *map)
 {
-	spin_lock_bh(&map_idr_lock);
-	map = __bpf_map_inc_not_zero(map, false);
-	spin_unlock_bh(&map_idr_lock);
-
-	return map;
+	lockdep_assert(rcu_read_lock_held());
+	return __bpf_map_inc_not_zero(map, false);
 }
 EXPORT_SYMBOL_GPL(bpf_map_inc_not_zero);