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@xxxxxxxxx>
Cc: Martin Habets <habetsm.xilinx@xxxxxxxxx>
Acked-by: Edward Cree <ecree.xilinx@xxxxxxxxx>
Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
---
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
