dmaengine: mv_xor: fix oops when channels fail to initialise

When a channel fails to initialise, we error out and clean up any
previously unregistered channels by walking the entire xordev->channels
array.  Unfortunately, there are paths which end up storing an error
pointer in this array, which we then try and dereference in the cleanup
code, which causes an oops.

Fix this by avoiding writing invalid pointers to this array in the first
place.

Tested-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/dma/mv_xor.c

@@ -1199,6 +1199,7 @@ static int mv_xor_probe(struct platform_device *pdev)
 		int i = 0;
 
 		for_each_child_of_node(pdev->dev.of_node, np) {
+			struct mv_xor_chan *chan;
 			dma_cap_mask_t cap_mask;
 			int irq;
 
@@ -1216,21 +1217,21 @@ static int mv_xor_probe(struct platform_device *pdev)
 				goto err_channel_add;
 			}
 
-			xordev->channels[i] =
-				mv_xor_channel_add(xordev, pdev, i,
-						   cap_mask, irq);
-			if (IS_ERR(xordev->channels[i])) {
-				ret = PTR_ERR(xordev->channels[i]);
-				xordev->channels[i] = NULL;
+			chan = mv_xor_channel_add(xordev, pdev, i,
+						  cap_mask, irq);
+			if (IS_ERR(chan)) {
+				ret = PTR_ERR(chan);
 				irq_dispose_mapping(irq);
 				goto err_channel_add;
 			}
 
+			xordev->channels[i] = chan;
 			i++;
 		}
 	} else if (pdata && pdata->channels) {
 		for (i = 0; i < MV_XOR_MAX_CHANNELS; i++) {
 			struct mv_xor_channel_data *cd;
+			struct mv_xor_chan *chan;
 			int irq;
 
 			cd = &pdata->channels[i];
@@ -1245,13 +1246,14 @@ static int mv_xor_probe(struct platform_device *pdev)
 				goto err_channel_add;
 			}
 
-			xordev->channels[i] =
-				mv_xor_channel_add(xordev, pdev, i,
-						   cd->cap_mask, irq);
-			if (IS_ERR(xordev->channels[i])) {
-				ret = PTR_ERR(xordev->channels[i]);
+			chan = mv_xor_channel_add(xordev, pdev, i,
+						  cd->cap_mask, irq);
+			if (IS_ERR(chan)) {
+				ret = PTR_ERR(chan);
 				goto err_channel_add;
 			}
+
+			xordev->channels[i] = chan;
 		}
 	}