[PATCH net] net: renesas: rswitch: handle stop vs interrupt race

[Nikita Yushchenko <nikita.yoush@xxxxxxxxxxxxxxxxxx>]

Currently the stop routine of rswitch driver does not immediately
prevent hardware from continuing to update descriptors and requesting
interrupts.

It can happen that when rswitch_stop() executes the masking of
interrupts from the queues of the port being closed, napi poll for
that port is already scheduled or running on a different CPU. When
execution of this napi poll completes, it will unmask the interrupts.
And unmasked interrupt can fire after rswitch_stop() returns from
napi_disable() call. Then, the handler won't mask it, because
napi_schedule_prep() will return false, and interrupt storm will
happen.

This can't be fixed by making rswitch_stop() call napi_disable() before
masking interrupts. In this case, the interrupt storm will happen if
interrupt fires between napi_disable() and masking.

Fix this by checking for priv->opened_ports bit when unmasking
interrupts after napi poll. For that to be consistent, move
priv->opened_ports changes into spinlock-protected areas, and reorder
other operations in rswitch_open() and rswitch_stop() accordingly.

Signed-off-by: Nikita Yushchenko <nikita.yoush@xxxxxxxxxxxxxxxxxx>
---
 drivers/net/ethernet/renesas/rswitch.c | 33 ++++++++++++++------------
 1 file changed, 18 insertions(+), 15 deletions(-)

diff --git a/drivers/net/ethernet/renesas/rswitch.c b/drivers/net/ethernet/renesas/rswitch.c
index 6ca5f72193eb..a33f74e1c447 100644
--- a/drivers/net/ethernet/renesas/rswitch.c
+++ b/drivers/net/ethernet/renesas/rswitch.c
@@ -918,8 +918,10 @@ static int rswitch_poll(struct napi_struct *napi, int budget)
 
 	if (napi_complete_done(napi, budget - quota)) {
 		spin_lock_irqsave(&priv->lock, flags);
-		rswitch_enadis_data_irq(priv, rdev->tx_queue->index, true);
-		rswitch_enadis_data_irq(priv, rdev->rx_queue->index, true);
+		if (test_bit(rdev->port, priv->opened_ports)) {
+			rswitch_enadis_data_irq(priv, rdev->tx_queue->index, true);
+			rswitch_enadis_data_irq(priv, rdev->rx_queue->index, true);
+		}
 		spin_unlock_irqrestore(&priv->lock, flags);
 	}
 
@@ -1582,20 +1584,20 @@ static int rswitch_open(struct net_device *ndev)
 	struct rswitch_device *rdev = netdev_priv(ndev);
 	unsigned long flags;
 
-	phy_start(ndev->phydev);
+	if (bitmap_empty(rdev->priv->opened_ports, RSWITCH_NUM_PORTS))
+		iowrite32(GWCA_TS_IRQ_BIT, rdev->priv->addr + GWTSDIE);
 
 	napi_enable(&rdev->napi);
-	netif_start_queue(ndev);
 
 	spin_lock_irqsave(&rdev->priv->lock, flags);
+	bitmap_set(rdev->priv->opened_ports, rdev->port, 1);
 	rswitch_enadis_data_irq(rdev->priv, rdev->tx_queue->index, true);
 	rswitch_enadis_data_irq(rdev->priv, rdev->rx_queue->index, true);
 	spin_unlock_irqrestore(&rdev->priv->lock, flags);
 
-	if (bitmap_empty(rdev->priv->opened_ports, RSWITCH_NUM_PORTS))
-		iowrite32(GWCA_TS_IRQ_BIT, rdev->priv->addr + GWTSDIE);
+	phy_start(ndev->phydev);
 
-	bitmap_set(rdev->priv->opened_ports, rdev->port, 1);
+	netif_start_queue(ndev);
 
 	return 0;
 };
@@ -1607,7 +1609,16 @@ static int rswitch_stop(struct net_device *ndev)
 	unsigned long flags;
 
 	netif_tx_stop_all_queues(ndev);
+
+	phy_stop(ndev->phydev);
+
+	spin_lock_irqsave(&rdev->priv->lock, flags);
+	rswitch_enadis_data_irq(rdev->priv, rdev->tx_queue->index, false);
+	rswitch_enadis_data_irq(rdev->priv, rdev->rx_queue->index, false);
 	bitmap_clear(rdev->priv->opened_ports, rdev->port, 1);
+	spin_unlock_irqrestore(&rdev->priv->lock, flags);
+
+	napi_disable(&rdev->napi);
 
 	if (bitmap_empty(rdev->priv->opened_ports, RSWITCH_NUM_PORTS))
 		iowrite32(GWCA_TS_IRQ_BIT, rdev->priv->addr + GWTSDID);
@@ -1620,14 +1631,6 @@ static int rswitch_stop(struct net_device *ndev)
 		kfree(ts_info);
 	}
 
-	spin_lock_irqsave(&rdev->priv->lock, flags);
-	rswitch_enadis_data_irq(rdev->priv, rdev->tx_queue->index, false);
-	rswitch_enadis_data_irq(rdev->priv, rdev->rx_queue->index, false);
-	spin_unlock_irqrestore(&rdev->priv->lock, flags);
-
-	phy_stop(ndev->phydev);
-	napi_disable(&rdev->napi);
-
 	return 0;
 };
 
-- 
2.39.5