bpf, devmap: Pass lockdep expression to RCU lists

head is traversed using hlist_for_each_entry_rcu outside an RCU
read-side critical section but under the protection of dtab->index_lock.

Hence, add corresponding lockdep expression to silence false-positive
lockdep warnings, and harden RCU lists.

Fixes: 6f9d451ab1a3 ("xdp: Add devmap_hash map type for looking up devices by hashed index")
Signed-off-by: Amol Grover <frextrite@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20200123120437.26506-1-frextrite@gmail.com

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index de630f9..f3a44f6 100644 (file)
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -263,7 +263,8 @@ struct bpf_dtab_netdev *__dev_map_hash_lookup_elem(struct bpf_map *map, u32 key)
        struct hlist_head *head = dev_map_index_hash(dtab, key);
        struct bpf_dtab_netdev *dev;
 
-       hlist_for_each_entry_rcu(dev, head, index_hlist)
+       hlist_for_each_entry_rcu(dev, head, index_hlist,
+                                lockdep_is_held(&dtab->index_lock))
                if (dev->idx == key)
                        return dev;