Commit 0cc84b9a authored Jun 24, 2021 by Toke Høiland-Jørgensen Committed by Daniel Borkmann Jun 24, 2021

ti: Remove rcu_read_lock() around XDP program invocation

The cpsw 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 <toke@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Grygorii Strashko <grygorii.strashko@ti.com>
Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: linux-omap@vger.kernel.org
Link: https://lore.kernel.org/bpf/20210624160609.292325-20-toke@redhat.com

parent 2f1e432d

drivers/net/ethernet/ti/cpsw_priv.c

+2 −8

Original line number	Diff line number	Diff line
		@@ -1328,13 +1328,9 @@ int cpsw_run_xdp(struct cpsw_priv priv, int ch, struct xdp_buff xdp,
		struct bpf_prog *prog;
		u32 act;

		rcu_read_lock();

		prog = READ_ONCE(priv->xdp_prog);
		if (!prog) {
		ret = CPSW_XDP_PASS;
		goto out;
		}
		if (!prog)
		return CPSW_XDP_PASS;

		act = bpf_prog_run_xdp(prog, xdp);
		/* XDP prog might have changed packet data and boundaries */
		@@ -1378,10 +1374,8 @@ int cpsw_run_xdp(struct cpsw_priv priv, int ch, struct xdp_buff xdp,
		ndev->stats.rx_bytes += *len;
		ndev->stats.rx_packets++;
		out:
		rcu_read_unlock();
		return ret;
		drop:
		rcu_read_unlock();
		page_pool_recycle_direct(cpsw->page_pool[ch], page);
		return ret;
		}