i2c: rcar: avoid race when unregistering slave client

After we disabled interrupts, there might still be an active one
running. Sync before clearing the pointer to the slave device.

Fixes: de20d18 ("i2c: rcar: add slave support")
Reported-by: Krzysztof Adamski <krzysztof.adamski@nokia.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Krzysztof Adamski <krzysztof.adamski@nokia.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-rcar.c

@@ -139,6 +139,7 @@ struct rcar_i2c_priv {
 	enum dma_data_direction dma_direction;
 
 	struct reset_control *rstc;
+	int irq;
 };
 
 #define rcar_i2c_priv_to_dev(p)		((p)->adap.dev.parent)
@@ -861,9 +862,11 @@ static int rcar_unreg_slave(struct i2c_client *slave)
 
 	WARN_ON(!priv->slave);
 
+	/* disable irqs and ensure none is running before clearing ptr */
 	rcar_i2c_write(priv, ICSIER, 0);
 	rcar_i2c_write(priv, ICSCR, 0);
 
+	synchronize_irq(priv->irq);
 	priv->slave = NULL;
 
 	pm_runtime_put(rcar_i2c_priv_to_dev(priv));
@@ -918,7 +921,7 @@ static int rcar_i2c_probe(struct platform_device *pdev)
 	struct i2c_adapter *adap;
 	struct device *dev = &pdev->dev;
 	struct i2c_timings i2c_t;
-	int irq, ret;
+	int ret;
 
 	/* Otherwise logic will break because some bytes must always use PIO */
 	BUILD_BUG_ON_MSG(RCAR_MIN_DMA_LEN < 3, "Invalid min DMA length");
@@ -984,10 +987,10 @@ static int rcar_i2c_probe(struct platform_device *pdev)
 		pm_runtime_put(dev);
 
 
-	irq = platform_get_irq(pdev, 0);
-	ret = devm_request_irq(dev, irq, rcar_i2c_irq, 0, dev_name(dev), priv);
+	priv->irq = platform_get_irq(pdev, 0);
+	ret = devm_request_irq(dev, priv->irq, rcar_i2c_irq, 0, dev_name(dev), priv);
 	if (ret < 0) {
-		dev_err(dev, "cannot get irq %d\n", irq);
+		dev_err(dev, "cannot get irq %d\n", priv->irq);
 		goto out_pm_disable;
 	}