mmc: moxart: Fix reference count leaks in moxart_probe

The issue happens in several error handling paths on two refcounted
object related to the object "host" (dma_chan_rx, dma_chan_tx). In
these paths, the function forgets to decrement one or both objects'
reference count increased earlier by dma_request_chan(), causing
reference count leaks.

Fix it by balancing the refcounts of both objects in some error
handling paths. In correspondence with the changes in moxart_probe(),
IS_ERR() is replaced with IS_ERR_OR_NULL() in moxart_remove() as well.
Signed-off-by: Xin Xiong <xiongx18@fudan.edu.cn>
Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
Link: https://lore.kernel.org/r/20211009041918.28419-1-xiongx18@fudan.edu.cnSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/moxart-mmc.c

@@ -621,6 +621,14 @@ static int moxart_probe(struct platform_device *pdev)
 			ret = -EPROBE_DEFER;
 			goto out;
 		}
+		if (!IS_ERR(host->dma_chan_tx)) {
+			dma_release_channel(host->dma_chan_tx);
+			host->dma_chan_tx = NULL;
+		}
+		if (!IS_ERR(host->dma_chan_rx)) {
+			dma_release_channel(host->dma_chan_rx);
+			host->dma_chan_rx = NULL;
+		}
 		dev_dbg(dev, "PIO mode transfer enabled\n");
 		host->have_dma = false;
 	} else {
@@ -675,6 +683,10 @@ static int moxart_probe(struct platform_device *pdev)
 	return 0;
 
 out:
+	if (!IS_ERR_OR_NULL(host->dma_chan_tx))
+		dma_release_channel(host->dma_chan_tx);
+	if (!IS_ERR_OR_NULL(host->dma_chan_rx))
+		dma_release_channel(host->dma_chan_rx);
 	if (mmc)
 		mmc_free_host(mmc);
 	return ret;
@@ -687,9 +699,9 @@ static int moxart_remove(struct platform_device *pdev)
 
 	dev_set_drvdata(&pdev->dev, NULL);
 
-	if (!IS_ERR(host->dma_chan_tx))
+	if (!IS_ERR_OR_NULL(host->dma_chan_tx))
 		dma_release_channel(host->dma_chan_tx);
-	if (!IS_ERR(host->dma_chan_rx))
+	if (!IS_ERR_OR_NULL(host->dma_chan_rx))
 		dma_release_channel(host->dma_chan_rx);
 	mmc_remove_host(mmc);
 	mmc_free_host(mmc);