[PATCH net v2 2/2] net: spacemit: Hold RTNL lock in emac_resume() and emac_suspend()

[Ali Tariq]

The emac_resume() calls the emac_open() and emac_suspend() calls
emac_stop() functions directly without holding the lock through
rtnl_lock(). These functions rely on phy_disconnect() which reads pointer
with rtnl_dereference(). But since no lock is being held,
rtnl_dereference throws a suspicious RCU usage on
Orange Pi RV2 (SpacemiT K1) warning when lockdep is enabled.

WARNING: suspicious RCU usage
drivers/net/phy/phy_device.c:1831 suspicious rcu_dereference_protected() usage!
Call Trace:
phy_detach_internal+0x490/0x5f2
phy_disconnect+0x90/0xc0
emac_stop+0x114/0x626
emac_suspend+0xac/0x126
platform_pm_suspend+0x72/0xe4

Take RTNL in emac_suspend() and emac_resume() before the netif_running()
checks, so the interface can't be opened or closed between the check and
emac_stop() or emac_open().

Found by CI suspend tests on Orange Pi RV2 (SpacemiT K1). Tested on the
same board with lockdep enabled: 12 suspend/resume cycles without the
warning, and kselftest with no new failures.

Fixes: bfec6d7f2001 ("net: spacemit: Add K1 Ethernet MAC")
Signed-off-by: Ali Tariq <alitariq45892 at gmail.com>
---
Changes in v2:
- Moved the rtnl_lock() before the 'running' flag check
Warning Log: https://kernelci.cloud-v.co/scheduler/job/549#L2168
Fixed Log: https://kernelci.cloud-v.co/scheduler/job/589
---
 drivers/net/ethernet/spacemit/k1_emac.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/spacemit/k1_emac.c b/drivers/net/ethernet/spacemit/k1_emac.c
index 51edc95f54c8..d07d8a1aa5ee 100644
--- a/drivers/net/ethernet/spacemit/k1_emac.c
+++ b/drivers/net/ethernet/spacemit/k1_emac.c
@@ -2031,11 +2031,16 @@ static int emac_resume(struct device *dev)
 		dev_err(dev, "Failed to enable bus clock: %d\n", ret);
 		return ret;
 	}
+	rtnl_lock();
 
-	if (!netif_running(ndev))
+	if (!netif_running(ndev)) {
+		rtnl_unlock();
 		return 0;
+	}
 
 	ret = emac_open(ndev);
+	rtnl_unlock();
+
 	if (ret) {
 		clk_disable_unprepare(priv->bus_clk);
 		return ret;
@@ -2055,12 +2060,16 @@ static int emac_suspend(struct device *dev)
 
 	disable_work_sync(&priv->tx_timeout_task);
 
+	rtnl_lock();
+
 	if (!ndev || !netif_running(ndev)) {
+		rtnl_unlock();
 		clk_disable_unprepare(priv->bus_clk);
 		return 0;
 	}
 
 	emac_stop(ndev);
+	rtnl_unlock();
 
 	clk_disable_unprepare(priv->bus_clk);
 	netif_device_detach(ndev);
-- 
2.34.1