pciback: properly clean up after calling pcistub_device_find()

As the function calls pcistub_device_get() before returning non-NULL,
its callers need to take care of calling pcistub_device_put() on
(mostly, but not exclusively) error paths.

Otoh, the function already guarantees that the 'dev' member is non-NULL
upon successful return, so callers do not need to check for this a
second time.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/drivers/xen/pciback/pci_stub.c
+++ b/drivers/xen/pciback/pci_stub.c
@@ -642,14 +642,14 @@ static pci_ers_result_t pciback_slot_res
 		dev_err(&dev->dev, "pciback device is not connected or owned"
 			" by HVM, kill it\n");
 		kill_domain_by_device(psdev);
-		goto release;
+		goto end;
 	}
 
 	if ( !test_bit(_XEN_PCIB_AERHANDLER, 
 		(unsigned long *)&psdev->pdev->sh_info->flags) ) {
 		dev_err(&dev->dev, 
 			"guest with no AER driver should have been killed\n");
-		goto release;
+		goto end;
 	}
 	result = common_process(psdev, 1, XEN_PCI_OP_aer_slotreset, result);
 
@@ -659,9 +659,9 @@ static pci_ers_result_t pciback_slot_res
 			"No AER slot_reset service or disconnected!\n");
 		kill_domain_by_device(psdev);
 	}
-release:
-	pcistub_device_put(psdev);
 end:
+	if (psdev)
+		pcistub_device_put(psdev);
 	up_write(&pcistub_sem);
 	return result;
 
@@ -702,14 +702,14 @@ static pci_ers_result_t pciback_mmio_ena
 		dev_err(&dev->dev, "pciback device is not connected or owned"
 			" by HVM, kill it\n");
 		kill_domain_by_device(psdev);
-		goto release;
+		goto end;
 	}
 
 	if ( !test_bit(_XEN_PCIB_AERHANDLER, 
 		(unsigned long *)&psdev->pdev->sh_info->flags) ) {
 		dev_err(&dev->dev, 
 			"guest with no AER driver should have been killed\n");
-		goto release;
+		goto end;
 	}
 	result = common_process(psdev, 1, XEN_PCI_OP_aer_mmio, result);
 
@@ -719,9 +719,9 @@ static pci_ers_result_t pciback_mmio_ena
 			"No AER mmio_enabled service or disconnected!\n");
 		kill_domain_by_device(psdev);
 	}
-release:
-	pcistub_device_put(psdev);
 end:
+	if (psdev)
+		pcistub_device_put(psdev);
 	up_write(&pcistub_sem);
 	return result;
 }
@@ -762,7 +762,7 @@ static pci_ers_result_t pciback_error_de
 		dev_err(&dev->dev, "pciback device is not connected or owned"
 			" by HVM, kill it\n");
 		kill_domain_by_device(psdev);
-		goto release;
+		goto end;
 	}
 
 	/*Guest owns the device yet no aer handler regiested, kill guest*/
@@ -770,7 +770,7 @@ static pci_ers_result_t pciback_error_de
 		(unsigned long *)&psdev->pdev->sh_info->flags) ) {
 		dev_dbg(&dev->dev, "guest may have no aer driver, kill it\n");
 		kill_domain_by_device(psdev);
-		goto release;
+		goto end;
 	}
 	result = common_process(psdev, error, XEN_PCI_OP_aer_detected, result);
 
@@ -780,9 +780,9 @@ static pci_ers_result_t pciback_error_de
 			"No AER error_detected service or disconnected!\n");
 		kill_domain_by_device(psdev);
 	}
-release:
-	pcistub_device_put(psdev);
 end:
+	if (psdev)
+		pcistub_device_put(psdev);
 	up_write(&pcistub_sem);
 	return result;
 }
@@ -818,7 +818,7 @@ static void pciback_error_resume(struct 
 		dev_err(&dev->dev, "pciback device is not connected or owned"
 			" by HVM, kill it\n");
 		kill_domain_by_device(psdev);
-		goto release;
+		goto end;
 	}
 
 	if ( !test_bit(_XEN_PCIB_AERHANDLER, 
@@ -826,12 +826,12 @@ static void pciback_error_resume(struct 
 		dev_err(&dev->dev, 
 			"guest with no AER driver should have been killed\n");
 		kill_domain_by_device(psdev);
-		goto release;
+		goto end;
 	}
 	common_process(psdev, 1, XEN_PCI_OP_aer_resume, PCI_ERS_RESULT_RECOVERED);
-release:
-	pcistub_device_put(psdev);
 end:
+	if (psdev)
+		pcistub_device_put(psdev);
 	up_write(&pcistub_sem);
 	return;
 }
@@ -988,7 +988,7 @@ static int pcistub_reg_add(int domain, i
 	struct config_field *field;
 
 	psdev = pcistub_device_find(domain, bus, slot, func);
-	if (!psdev || !psdev->dev) {
+	if (!psdev) {
 		err = -ENODEV;
 		goto out;
 	}
@@ -1012,6 +1012,8 @@ static int pcistub_reg_add(int domain, i
 	if (err)
 		kfree(field);
       out:
+	if (psdev)
+		pcistub_device_put(psdev);
 	return err;
 }
 
@@ -1163,10 +1165,7 @@ static ssize_t permissive_add(struct dev
 		err = -ENODEV;
 		goto out;
 	}
-	if (!psdev->dev) {
-		err = -ENODEV;
-		goto release;
-	}
+
 	dev_data = pci_get_drvdata(psdev->dev);
 	/* the driver data for a device should never be null at this point */
 	if (!dev_data) {
@@ -1219,14 +1218,18 @@ DRIVER_ATTR(permissive, S_IRUSR | S_IWUS
 int pciback_get_owner(struct pci_dev *dev)
 {
 	struct pcistub_device *psdev;
+	int rc;
 
 	psdev = pcistub_device_find(pci_domain_nr(dev->bus), dev->bus->number,
 			PCI_SLOT(dev->devfn), PCI_FUNC(dev->devfn));
 
-	if (!psdev || !psdev->pdev)
-		return -1;
+	if (!psdev)
+		return -ESRCH;
+
+	rc = psdev->pdev ? psdev->pdev->xdev->otherend_id : -EINVAL;
 
-	return psdev->pdev->xdev->otherend_id;
+	pcistub_device_put(psdev);
+	return rc;
 }
 #endif