[PATCH net 16/16] can: mcp251xfd: flush RX offload queue during long IRQs

[Marc Kleine-Budde <mkl@pengutronix.de>]

From: Chris Strong <chris.strong@flocksafety.com>

Under sustained receive traffic, the threaded interrupt handler can
continue draining the controller indefinitely. Received SKBs remain in
skb_irq_queue until the handler returns, but the overflow checks inspect
the NAPI-visible skb_queue instead. The IRQ-local queue can therefore grow
without bound while NAPI remains unscheduled, potentially exhausting
memory.

Stop the dedicated RX loop when the IRQ-local queue reaches the NAPI weight
so TEF and other pending interrupts are processed before publishing the
batch. Publish further batches from the main interrupt loop while the
controller remains busy. This bounds IRQ-local accumulation and keeps RX
and TEF timestamps from each controller-status pass in the same sort
window.

Fixes: c757096ea103 ("can: rx-offload: add skb queue for use during ISR")
Assisted-by: LLM
Signed-off-by: Chris Strong <chris.strong@flocksafety.com>
Link: https://patch.msgid.link/20260929-upstream-can-rx-offload-batching-v2-2-3b587c519f5d@flocksafety.com
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---
 drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
index 8759bc05bd8f..26d6a0d4b34b 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
@@ -1498,8 +1498,14 @@ static irqreturn_t mcp251xfd_irq(int irq, void *dev_id)
 			/* We don't know which RX-FIFO is pending, but only
 			 * handle the 1st RX-FIFO. Leave loop here if we have
 			 * more than 1 RX-FIFO to avoid starvation.
+			 *
+			 * Once the IRQ queue reaches the NAPI weight, process
+			 * TEF and other pending interrupts before publishing
+			 * the batch, keeping RX and TEF timestamps in the same
+			 * sort window.
 			 */
-		} while (priv->rx_ring_num == 1);
+		} while (priv->rx_ring_num == 1 &&
+			 !can_rx_offload_irq_queue_needs_flush(&priv->offload));
 
 	do {
 		u32 intf_pending, intf_pending_clearable;
@@ -1615,6 +1621,12 @@ static irqreturn_t mcp251xfd_irq(int irq, void *dev_id)
 			}
 		}
 
+		/* Keep each splice into the offload queue near one NAPI poll
+		 * budget when a busy controller keeps this handler running.
+		 */
+		if (can_rx_offload_irq_queue_needs_flush(&priv->offload))
+			can_rx_offload_threaded_irq_finish(&priv->offload);
+
 		handled = IRQ_HANDLED;
 	} while (1);
 
-- 
2.53.0