can: rx-offload: can_rx_offload_threaded_irq_finish(): add new function to be called from threaded interrupt

After reading all CAN frames from the controller in the IRQ handler
and storing them into a skb_queue, the driver calls napi_schedule().
In the napi poll function the skb from the skb_queue are then pushed
into the networking stack.

However if napi_schedule() is called from a threaded IRQ handler this
triggers the following error:

| NOHZ tick-stop error: Non-RCU local softirq work is pending, handler thesofproject#8!!!

To avoid this, create a new rx-offload
function (can_rx_offload_threaded_irq_finish()) with a call to
local_bh_disable()/local_bh_enable() around the napi_schedule() call.

Convert all drivers that call can_rx_offload_irq_finish() from
threaded IRQ context to can_rx_offload_threaded_irq_finish().

Link: https://lore.kernel.org/r/20210724204745.736053-4-mkl@pengutronix.de
Suggested-by: Daniel Glöckner <dg@emlix.com>
Tested-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

Author: marckleinebudde

drivers/net/can/dev/rx-offload.c

@@ -299,6 +299,29 @@ void can_rx_offload_irq_finish(struct can_rx_offload *offload)
 }
 EXPORT_SYMBOL_GPL(can_rx_offload_irq_finish);
 
+void can_rx_offload_threaded_irq_finish(struct can_rx_offload *offload)
+{
+	unsigned long flags;
+	int queue_len;
+
+	if (skb_queue_empty_lockless(&offload->skb_irq_queue))
+		return;
+
+	spin_lock_irqsave(&offload->skb_queue.lock, flags);
+	skb_queue_splice_tail_init(&offload->skb_irq_queue, &offload->skb_queue);
+	spin_unlock_irqrestore(&offload->skb_queue.lock, flags);
+
+	queue_len = skb_queue_len(&offload->skb_queue);
+	if (queue_len > offload->skb_queue_len_max / 8)
+		netdev_dbg(offload->dev, "%s: queue_len=%d\n",
+			   __func__, queue_len);
+
+	local_bh_disable();
+	napi_schedule(&offload->napi);
+	local_bh_enable();
+}
+EXPORT_SYMBOL_GPL(can_rx_offload_threaded_irq_finish);
+
 static int can_rx_offload_init_queue(struct net_device *dev,
 				     struct can_rx_offload *offload,
 				     unsigned int weight)

drivers/net/can/m_can/m_can.c

@@ -1059,7 +1059,7 @@ static irqreturn_t m_can_isr(int irq, void *dev_id)
 	}
 
 	if (cdev->is_peripheral)
-		can_rx_offload_irq_finish(&cdev->offload);
+		can_rx_offload_threaded_irq_finish(&cdev->offload);
 
 	return IRQ_HANDLED;
 }

drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c

@@ -2196,7 +2196,7 @@ static irqreturn_t mcp251xfd_irq(int irq, void *dev_id)
 				  priv->regs_status.intf);
 
 		if (!(intf_pending)) {
-			can_rx_offload_irq_finish(&priv->offload);
+			can_rx_offload_threaded_irq_finish(&priv->offload);
 			return handled;
 		}
 
@@ -2298,7 +2298,7 @@ static irqreturn_t mcp251xfd_irq(int irq, void *dev_id)
 	} while (1);
 
  out_fail:
-	can_rx_offload_irq_finish(&priv->offload);
+	can_rx_offload_threaded_irq_finish(&priv->offload);
 
 	netdev_err(priv->ndev, "IRQ handler returned %d (intf=0x%08x).\n",
 		   err, priv->regs_status.intf);

include/linux/can/rx-offload.h

@@ -50,6 +50,7 @@ unsigned int can_rx_offload_get_echo_skb(struct can_rx_offload *offload,
 int can_rx_offload_queue_tail(struct can_rx_offload *offload,
 			      struct sk_buff *skb);
 void can_rx_offload_irq_finish(struct can_rx_offload *offload);
+void can_rx_offload_threaded_irq_finish(struct can_rx_offload *offload);
 void can_rx_offload_del(struct can_rx_offload *offload);
 void can_rx_offload_enable(struct can_rx_offload *offload);