The nfp 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. While this is not actually an issue for the nfp driver because it doesn't support XDP_REDIRECT (and thus doesn't call xdp_do_flush()), the rcu_read_lock() is still unneeded. And 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: Simon Horman <simon.horman@xxxxxxxxxxxxx> Cc: oss-drivers@xxxxxxxxxxxxx Reviewed-by: Simon Horman <simon.horman@xxxxxxxxxxxxx> Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx> --- drivers/net/ethernet/netronome/nfp/nfp_net_common.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c index eeb30680b4dc..a3d59abed6ae 100644 --- a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c +++ b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c @@ -1819,7 +1819,6 @@ static int nfp_net_rx(struct nfp_net_rx_ring *rx_ring, int budget) struct xdp_buff xdp; int idx; - rcu_read_lock(); xdp_prog = READ_ONCE(dp->xdp_prog); true_bufsz = xdp_prog ? PAGE_SIZE : dp->fl_bufsz; xdp_init_buff(&xdp, PAGE_SIZE - NFP_NET_RX_BUF_HEADROOM, @@ -1919,6 +1918,10 @@ static int nfp_net_rx(struct nfp_net_rx_ring *rx_ring, int budget) pkt_off - NFP_NET_RX_BUF_HEADROOM, pkt_len, true); + /* This code is invoked within a single NAPI poll cycle + * and thus under local_bh_disable(), which provides the + * needed RCU protection. + */ act = bpf_prog_run_xdp(xdp_prog, &xdp); pkt_len = xdp.data_end - xdp.data; @@ -2036,7 +2039,6 @@ static int nfp_net_rx(struct nfp_net_rx_ring *rx_ring, int budget) if (!nfp_net_xdp_complete(tx_ring)) pkts_polled = budget; } - rcu_read_unlock(); return pkts_polled; } -- 2.31.1
