From: Toke Høiland-Jørgensen Date: Thu, 24 Jun 2021 16:06:06 +0000 (+0200) Subject: sfc: Remove rcu_read_lock() around XDP program invocation X-Git-Tag: v5.15~843^2~14^2~8 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=4eb14e3fc6197b7205069ed4e2b31eafa11a0697;p=platform%2Fkernel%2Flinux-starfive.git sfc: Remove rcu_read_lock() around XDP program invocation 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. Signed-off-by: Toke Høiland-Jørgensen Signed-off-by: Daniel Borkmann Acked-by: Edward Cree Cc: Martin Habets Link: https://lore.kernel.org/bpf/20210624160609.292325-17-toke@redhat.com --- diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c index 17b8119..6067509 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()) @@ -296,7 +292,6 @@ static bool efx_do_xdp(struct efx_nic *efx, struct efx_channel *channel, rx_buf->len, false); xdp_act = bpf_prog_run_xdp(xdp_prog, &xdp); - rcu_read_unlock(); offset = (u8 *)xdp.data - *ehp;