[PATCH net 3/3] igb: add XDP transition guards in igb_xdp_setup()

[Alex Dvoretsky <advoretsky@gmail.com>]

igb_xdp_setup() calls igb_close() + igb_open() when transitioning
between XDP and non-XDP mode on a running device. This has two issues:

1. When removing an XDP program that has AF_XDP zero-copy sockets,
   ndo_xsk_wakeup() may be executing concurrently under rcu_read_lock().
   If igb_close() tears down the rings while ndo_xsk_wakeup() is still
   accessing them, it races with the teardown. Add synchronize_rcu()
   before igb_close() when removing an XDP program to ensure all
   in-flight ndo_xsk_wakeup() calls complete first.

2. The igb_close()/igb_open() window leaves trans_start stale from
   before the close: the TX watchdog can fire a spurious timeout and
   queue a reset_task that races with igb_open(). Add
   netif_trans_update() after igb_open() to refresh the timestamp, and
   cancel_work() to drain any reset_task queued during the window.

Fixes: 9cbc948b5a20 ("igb: add XDP support")
Cc: stable@vger.kernel.org
Signed-off-by: Alex Dvoretsky <advoretsky@gmail.com>
---
 drivers/net/ethernet/intel/igb/igb_main.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
index ddb7ce9e97bf..9ba944bf67b4 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -2913,6 +2913,9 @@ static int igb_xdp_setup(struct net_device *dev, struct netdev_bpf *bpf)
 
 	/* device is up and bpf is added/removed, must setup the RX queues */
 	if (need_reset && running) {
+		if (!prog)
+			/* Wait until ndo_xsk_wakeup completes. */
+			synchronize_rcu();
 		igb_close(dev);
 	} else {
 		for (i = 0; i < adapter->num_rx_queues; i++)
@@ -2936,6 +2939,16 @@ static int igb_xdp_setup(struct net_device *dev, struct netdev_bpf *bpf)
 	if (running)
 		igb_open(dev);
 
+	/* Refresh trans_start to prevent the TX watchdog from firing on a
+	 * stale timestamp from before igb_close(). Cancel any reset_task
+	 * that igb_tx_timeout() may have queued between igb_close() setting
+	 * __IGB_DOWN and the actual napi_synchronize() completion.
+	 */
+	if (need_reset && running) {
+		netif_trans_update(dev);
+		cancel_work(&adapter->reset_task);
+	}
+
 	return 0;
 }
 
-- 
2.51.0