[PATCH bpf-next v2 13/16] sfc: remove rcu_read_lock() around XDP program invocation
From: Toke Høiland-Jørgensen <hidden>
Date: 2021-06-15 15:04:31
Also in:
bpf
Subsystem:
networking drivers, sfc network driver, the rest · Maintainers:
Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Edward Cree, Linus Torvalds
The sfc 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. Cc: Edward Cree <ecree.xilinx@gmail.com> Cc: Martin Habets <redacted> Acked-by: Edward Cree <ecree.xilinx@gmail.com> Signed-off-by: Toke Høiland-Jørgensen <redacted> --- drivers/net/ethernet/sfc/rx.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-)
diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c
index 17b8119c48e5..3e5b88ab42db 100644
--- a/drivers/net/ethernet/sfc/rx.c
+++ b/drivers/net/ethernet/sfc/rx.c@@ -260,18 +260,14 @@ static bool efx_do_xdp(struct efx_nic *efx, struct efx_channel *channel, s16 offset; int err; - rcu_read_lock(); - xdp_prog = rcu_dereference(efx->xdp_prog); - if (!xdp_prog) { - rcu_read_unlock(); + xdp_prog = rcu_dereference_bh(efx->xdp_prog); + if (!xdp_prog) return true; - } rx_queue = efx_channel_get_rx_queue(channel); if (unlikely(channel->rx_pkt_n_frags > 1)) { /* We can't do XDP on fragmented packets - drop. */ - rcu_read_unlock(); efx_free_rx_buffers(rx_queue, rx_buf, channel->rx_pkt_n_frags); if (net_ratelimit())
@@ -295,8 +291,10 @@ static bool efx_do_xdp(struct efx_nic *efx, struct efx_channel *channel, xdp_prepare_buff(&xdp, *ehp - EFX_XDP_HEADROOM, EFX_XDP_HEADROOM, rx_buf->len, false); + /* This code is invoked within a single NAPI poll cycle and thus under + * local_bh_disable(), which provides the needed RCU protection. + */ xdp_act = bpf_prog_run_xdp(xdp_prog, &xdp); - rcu_read_unlock(); offset = (u8 *)xdp.data - *ehp;
--
2.31.1