[PATCH bpf-next v3 10/16] mlx4: remove rcu_read_lock() around XDP program invocation
From: Toke Høiland-Jørgensen <hidden>
Date: 2021-06-17 21:37:28
Also in:
bpf
Subsystem:
mellanox ethernet driver (mlx4_en), mellanox mlx4 core vpi driver, networking drivers, the rest · Maintainers:
Tariq Toukan, Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
The mlx4 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. Also switch the RCU dereferences in the driver loop itself to the _bh variants. Cc: Tariq Toukan <tariqt@nvidia.com> Reviewed-by: Tariq Toukan <tariqt@nvidia.com> Signed-off-by: Toke Høiland-Jørgensen <redacted> --- drivers/net/ethernet/mellanox/mlx4/en_rx.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)
diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
index e35e4d7ef4d1..3f08c14d0441 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c@@ -679,9 +679,7 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct mlx4_en_cq *cq, int bud ring = priv->rx_ring[cq_ring]; - /* Protect accesses to: ring->xdp_prog, priv->mac_hash list */ - rcu_read_lock(); - xdp_prog = rcu_dereference(ring->xdp_prog); + xdp_prog = rcu_dereference_bh(ring->xdp_prog); xdp_init_buff(&xdp, priv->frag_info[0].frag_stride, &ring->xdp_rxq); doorbell_pending = false;
@@ -744,7 +742,7 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct mlx4_en_cq *cq, int bud /* Drop the packet, since HW loopback-ed it */ mac_hash = ethh->h_source[MLX4_EN_MAC_HASH_IDX]; bucket = &priv->mac_hash[mac_hash]; - hlist_for_each_entry_rcu(entry, bucket, hlist) { + hlist_for_each_entry_rcu_bh(entry, bucket, hlist) { if (ether_addr_equal_64bits(entry->mac, ethh->h_source)) goto next;
@@ -899,8 +897,6 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct mlx4_en_cq *cq, int bud break; } - rcu_read_unlock(); - if (likely(polled)) { if (doorbell_pending) { priv->tx_cq[TX_XDP][cq_ring]->xdp_busy = true;
--
2.32.0