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[bpf-next,v3,11/16] nfp: remove rcu_read_lock() around XDP program invocation

Message ID 20210617212748.32456-12-toke@redhat.com
State New
Headers show
Series [bpf-next,v3,01/16] rcu: Create an unrcu_pointer() to remove __rcu from a pointer | expand

Commit Message

Toke Høiland-Jørgensen June 17, 2021, 9:27 p.m. UTC
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

Cc: Simon Horman <simon.horman@netronome.com>
Cc: oss-drivers@netronome.com
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
 drivers/net/ethernet/netronome/nfp/nfp_net_common.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)
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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;