[PATCH net v2 1/2] net: spacemit: Fix TX timeout work deadlocking on itself

[Ali Tariq <alitariq45892@gmail.com>]

emac_tx_timeout_task() takes RTNL and calls dev_close(), which ends up
waiting for the work itself. The function call hierarchy is as follows

emac_tx_timeout_task()
    dev_close()
      emac_stop()
        emac_down()
          cancel_work_sync(&priv->tx_timeout_task)

The work never finishes and keeps RTNL held, so after a TX timeout
everything that needs RTNL hangs.

Remove cancel_work_sync() from emac_down(). Disable the work in
emac_suspend() instead, and enable it again in emac_resume(). emac_remove()
runs before the devm-managed unregister_netdev(), so use
disable_work_sync() there to stop the work from being queued again.

Found by code inspection. Not reproduced on hardware. Tested on Orange
Pi RV2 (SpacemiT K1) with suspend/resume cycles and kselftest, with
lockdep enabled.

Fixes: bfec6d7f2001 ("net: spacemit: Add K1 Ethernet MAC")
Reported-by: Troy Mitchell <troy.mitchell@linux.spacemit.com>
Closes: https://lore.kernel.org/all/DMO74K2MG3D7.15UUOU1O66K6N@linux.spacemit.com/
Suggested-by: Vivian Wang <wangruikang@iscas.ac.cn>
Signed-off-by: Ali Tariq <alitariq45892@gmail.com>
---
 drivers/net/ethernet/spacemit/k1_emac.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/spacemit/k1_emac.c b/drivers/net/ethernet/spacemit/k1_emac.c
index 71a80838bffd..51edc95f54c8 100644
--- a/drivers/net/ethernet/spacemit/k1_emac.c
+++ b/drivers/net/ethernet/spacemit/k1_emac.c
@@ -1732,7 +1732,6 @@ static int emac_down(struct emac_priv *priv)
 	napi_disable(&priv->napi);
 
 	timer_delete_sync(&priv->txtimer);
-	cancel_work_sync(&priv->tx_timeout_task);
 
 	timer_delete_sync(&priv->stats_timer);
 
@@ -2010,8 +2009,9 @@ static void emac_remove(struct platform_device *pdev)
 {
 	struct emac_priv *priv = platform_get_drvdata(pdev);
 
+	disable_work_sync(&priv->tx_timeout_task);
+
 	timer_shutdown_sync(&priv->txtimer);
-	cancel_work_sync(&priv->tx_timeout_task);
 
 	timer_shutdown_sync(&priv->stats_timer);
 
@@ -2024,6 +2024,8 @@ static int emac_resume(struct device *dev)
 	struct net_device *ndev = priv->ndev;
 	int ret;
 
+	enable_work(&priv->tx_timeout_task);
+
 	ret = clk_prepare_enable(priv->bus_clk);
 	if (ret < 0) {
 		dev_err(dev, "Failed to enable bus clock: %d\n", ret);
@@ -2051,6 +2053,8 @@ static int emac_suspend(struct device *dev)
 	struct emac_priv *priv = dev_get_drvdata(dev);
 	struct net_device *ndev = priv->ndev;
 
+	disable_work_sync(&priv->tx_timeout_task);
+
 	if (!ndev || !netif_running(ndev)) {
 		clk_disable_unprepare(priv->bus_clk);
 		return 0;
-- 
2.34.1