ena: Remove rcu_read_lock() around XDP program invocation

The ena driver has rcu_read_lock()/rcu_read_unlock() pairs around XDP
program invocations. However, the actual lifetime of the objects referred
by the XDP program invocation is longer, all the way through to the call to
xdp_do_flush(), making the scope of the rcu_read_lock() too small. This
turns out to be harmless because it all happens in a single NAPI poll
cycle (and thus under local_bh_disable()), but it makes the rcu_read_lock()
misleading.

Rather than extend the scope of the rcu_read_lock(), just get rid of it
entirely. With the addition of RCU annotations to the XDP_REDIRECT map
types that take bh execution into account, lockdep even understands this to
be safe, so there's really no reason to keep it around.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Saeed Bishara <saeedb@amazon.com>
Cc: Guy Tzalik <gtzalik@amazon.com>
Link: https://lore.kernel.org/bpf/20210624160609.292325-8-toke@redhat.com

diff --git a/drivers/net/ethernet/amazon/ena/ena_netdev.c b/drivers/net/ethernet/amazon/ena/ena_netdev.c
index 3bb0e66..44ef6b8 100644 (file)
--- a/drivers/net/ethernet/amazon/ena/ena_netdev.c
+++ b/drivers/net/ethernet/amazon/ena/ena_netdev.c
@@ -382,7 +382,6 @@ static int ena_xdp_execute(struct ena_ring *rx_ring, struct xdp_buff *xdp)
        struct xdp_frame *xdpf;
        u64 *xdp_stat;
 
-       rcu_read_lock();
        xdp_prog = READ_ONCE(rx_ring->xdp_bpf_prog);
 
        if (!xdp_prog)
@@ -439,8 +438,6 @@ static int ena_xdp_execute(struct ena_ring *rx_ring, struct xdp_buff *xdp)
 
        ena_increase_stat(xdp_stat, 1, &rx_ring->syncp);
 out:
-       rcu_read_unlock();
-
        return verdict;
 }