[PATCH v9 3/8] serial: 8250_omap: serialize RX DMA completion and flushing

[James Hilliard <james.hilliard1@gmail.com>]

Moving RX DMA locking out of __dma_rx_do_complete() left the DMA
completion callback calling it without rx_dma_lock. Shutdown and runtime
suspend flush RX under rx_dma_lock but without the port lock, allowing
these paths to overlap the callback's buffer accounting and flip-buffer
insertion. RX submission and UART interrupt handling also require the
port lock.

Take rx_dma_lock inside the port lock in the completion callback. Hold
the port lock around the shutdown and runtime-suspend flushes, matching
the existing interrupt-path lock order. Assert both locks in the common
completion helper and the port lock at the flush entry point.

Fixes: 789898416749 ("serial: 8250: 8250_omap: Move locking out from __dma_rx_do_complete()")
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
---
 drivers/tty/serial/8250/8250_omap.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index b6f108d34854..322403cec2de 100644
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -771,8 +771,10 @@ static void omap_8250_shutdown(struct uart_port *port)
 	guard(serial8250_rpm)(up);
 
 	flush_work(&priv->qos_work);
-	if (up->dma)
+	if (up->dma) {
+		guard(uart_port_lock_irq)(port);
 		omap_8250_rx_dma_flush(up);
+	}
 
 	serial_out(up, UART_OMAP_WER, 0);
 	if (priv->habit & UART_HAS_EFR2)
@@ -898,7 +900,7 @@ static int omap8250_rs485_config(struct uart_port *port,
 #ifdef CONFIG_SERIAL_8250_DMA
 static int omap_8250_rx_dma(struct uart_8250_port *p);
 
-/* Must be called while priv->rx_dma_lock is held */
+/* Must be called with the port lock and priv->rx_dma_lock held. */
 static void __dma_rx_do_complete(struct uart_8250_port *p)
 {
 	struct uart_8250_dma    *dma = p->dma;
@@ -911,6 +913,9 @@ static void __dma_rx_do_complete(struct uart_8250_port *p)
 	int			ret;
 	u32			reg;
 
+	lockdep_assert_held_once(&p->port.lock);
+	lockdep_assert_held_once(&priv->rx_dma_lock);
+
 	if (!dma->rx_running)
 		goto out;
 
@@ -977,7 +982,8 @@ static void __dma_rx_complete(void *param)
 	if (dmaengine_tx_status(dma->rxchan, dma->rx_cookie, &state) != DMA_COMPLETE)
 		return;
 
-	__dma_rx_do_complete(p);
+	scoped_guard(spinlock, &priv->rx_dma_lock)
+		__dma_rx_do_complete(p);
 	if (priv->throttled)
 		return;
 
@@ -995,6 +1001,8 @@ static void omap_8250_rx_dma_flush(struct uart_8250_port *p)
 	unsigned long		flags;
 	int ret;
 
+	lockdep_assert_held_once(&p->port.lock);
+
 	spin_lock_irqsave(&priv->rx_dma_lock, flags);
 
 	if (!dma->rx_running) {
@@ -1811,8 +1819,10 @@ static int omap8250_runtime_suspend(struct device *dev)
 		}
 	}
 
-	if (up && up->dma && up->dma->rxchan)
+	if (up && up->dma && up->dma->rxchan) {
+		guard(uart_port_lock_irqsave)(&up->port);
 		omap_8250_rx_dma_flush(up);
+	}
 
 	priv->latency = PM_QOS_CPU_LATENCY_DEFAULT_VALUE;
 	schedule_work(&priv->qos_work);

-- 
2.53.0