[PATCH v1 bpf-next] net: core: allow netdev_upper_get_next_dev_rcu from bh context

[Kohei Enju <kohei@enjuk.jp>]

Since XDP programs are called from a NAPI poll context, the RCU
reference liveness is ensured by local_bh_disable().

Commit aeea1b86f936 ("bpf, devmap: Exclude XDP broadcast to master
device") started to call netdev_upper_get_next_dev_rcu() from this
context, but missed adding rcu_read_lock_bh_held() as a condition to the
RCU checks.
While both bh_disabled and rcu_read_lock() provide RCU protection,
lockdep complains since the check condition is insufficient [1].

Add rcu_read_lock_bh_held() as condition to help lockdep to understand
the dereference is safe, in the same way as commit 694cea395fde ("bpf:
Allow RCU-protected lookups to happen from bh context").

[1]
 WARNING: net/core/dev.c:8099 at netdev_upper_get_next_dev_rcu+0x96/0xd0, CPU#0: swapper/0/0
 ...
 RIP: 0010:netdev_upper_get_next_dev_rcu+0x96/0xd0
 ...
  <IRQ>
  dev_map_enqueue_multi+0x411/0x970
  xdp_do_redirect+0xdf2/0x1030
  __igc_xdp_run_prog+0x6a0/0xc80
  igc_poll+0x34b0/0x70b0
  __napi_poll.constprop.0+0x98/0x490
  net_rx_action+0x8f2/0xfa0
  handle_softirqs+0x1c7/0x710
  __irq_exit_rcu+0xb1/0xf0
  irq_exit_rcu+0x9/0x20
  common_interrupt+0x7f/0x90
  </IRQ>

Signed-off-by: Kohei Enju <kohei@enjuk.jp>
---
 net/core/dev.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 096b3ff13f6b..b99d46b682c6 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8103,7 +8103,8 @@ struct net_device *netdev_upper_get_next_dev_rcu(struct net_device *dev,
 {
 	struct netdev_adjacent *upper;
 
-	WARN_ON_ONCE(!rcu_read_lock_held() && !lockdep_rtnl_is_held());
+	WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_bh_held() &&
+		     !lockdep_rtnl_is_held());
 
 	upper = list_entry_rcu((*iter)->next, struct netdev_adjacent, list);
 
-- 
2.51.0