[PATCH net v4] ravb: Fix races between ravb_tx_timeout_work() and net related ops

[Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>]

Fix races between ravb_tx_timeout_work() and functions of net_device_ops
and ethtool_ops by using rtnl_trylock() and rtnl_unlock(). Note that
since ravb_close() is under the rtnl lock and calls cancel_work_sync(),
ravb_tx_timeout_work() should calls rtnl_trylock(). Otherwise, a deadlock
may happen in ravb_tx_timeout_work() like below:

CPU0			CPU1
			ravb_tx_timeout()
			schedule_work()
...
__dev_close_many()
// Under rtnl lock
ravb_close()
cancel_work_sync()
// Waiting
			ravb_tx_timeout_work()
			rtnl_lock()
			// This is possible to cause a deadlock

If rtnl_trylock() fails, rescheduling the work with sleep for 1 msec.

Fixes: c156633f1353 ("Renesas Ethernet AVB driver proper")
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
---
Changes from v3:
https://lore.kernel.org/all/20231115022644.2316961-1-yoshihiro.shimoda.uh@renesas.com/
 - Based on v2 patch. This means that delayed work is not used.
 - Add rescheduling the work if rtnl_trylock() fails.
 - Drop Reviewed-by tags because implementation was changed.

Changes from v2:
https://lore.kernel.org/netdev/20231019113308.1133944-1-yoshihiro.shimoda.uh@renesas.com/
 - Add rescheduling if rtnl_trylock() fails and the netif is still running
   and update commit description for it.
 - Add Reviewed-by tags.

 drivers/net/ethernet/renesas/ravb_main.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
index c70cff80cc99..7c007ecd3ff6 100644
--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c
@@ -1874,6 +1874,12 @@ static void ravb_tx_timeout_work(struct work_struct *work)
 	struct net_device *ndev = priv->ndev;
 	int error;
 
+	if (!rtnl_trylock()) {
+		usleep_range(1000, 2000);
+		schedule_work(&priv->work);
+		return;
+	}
+
 	netif_tx_stop_all_queues(ndev);
 
 	/* Stop PTP Clock driver */
@@ -1907,7 +1913,7 @@ static void ravb_tx_timeout_work(struct work_struct *work)
 		 */
 		netdev_err(ndev, "%s: ravb_dmac_init() failed, error %d\n",
 			   __func__, error);
-		return;
+		goto out_unlock;
 	}
 	ravb_emac_init(ndev);
 
@@ -1917,6 +1923,9 @@ static void ravb_tx_timeout_work(struct work_struct *work)
 		ravb_ptp_init(ndev, priv->pdev);
 
 	netif_tx_start_all_queues(ndev);
+
+out_unlock:
+	rtnl_unlock();
 }
 
 /* Packet transmit function for Ethernet AVB */
-- 
2.25.1