1 files changed, 85 insertions, 10 deletions

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index d74adb5bba44..33b524b4eb5e 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -45,7 +45,8 @@ struct vmbus_dynid {
 	struct hv_vmbus_device_id id;
 };
 
-static struct device  *hv_dev;
+/* VMBus Root Device */
+static struct device  *vmbus_root_device;
 
 static int hyperv_cpuhp_online;
 
@@ -80,9 +81,15 @@ static struct resource *fb_mmio;
 static struct resource *hyperv_mmio;
 static DEFINE_MUTEX(hyperv_mmio_lock);
 
+struct device *hv_get_vmbus_root_device(void)
+{
+	return vmbus_root_device;
+}
+EXPORT_SYMBOL_GPL(hv_get_vmbus_root_device);
+
 static int vmbus_exists(void)
 {
-	if (hv_dev == NULL)
+	if (vmbus_root_device == NULL)
 		return -ENODEV;
 
 	return 0;
@@ -707,7 +714,30 @@ static const struct hv_vmbus_device_id *hv_vmbus_get_id(const struct hv_driver *
 	return id;
 }
 
-/* vmbus_add_dynid - add a new device ID to this driver and re-probe devices */
+/* vmbus_add_dynid - add a new device ID to this driver and re-probe devices
+ *
+ * This function can race with vmbus_device_register(). This function is
+ * typically running on a user thread in response to writing to the "new_id"
+ * sysfs entry for a driver. vmbus_device_register() is running on a
+ * workqueue thread in response to the Hyper-V host offering a device to the
+ * guest. This function calls driver_attach(), which looks for an existing
+ * device matching the new id, and attaches the driver to which the new id
+ * has been assigned. vmbus_device_register() calls device_register(), which
+ * looks for a driver that matches the device being registered. If both
+ * operations are running simultaneously, the device driver probe function runs
+ * on whichever thread establishes the linkage between the driver and device.
+ *
+ * In most cases, it doesn't matter which thread runs the driver probe
+ * function. But if vmbus_device_register() does not find a matching driver,
+ * it proceeds to create the "channels" subdirectory and numbered per-channel
+ * subdirectory in sysfs. While that multi-step creation is in progress, this
+ * function could run the driver probe function. If the probe function checks
+ * for, or operates on, entries in the "channels" subdirectory, including by
+ * calling hv_create_ring_sysfs(), the operation may or may not succeed
+ * depending on the race. The race can't create a kernel failure in VMBus
+ * or device subsystem code, but probe functions in VMBus drivers doing such
+ * operations must be prepared for the failure case.
+ */
 static int vmbus_add_dynid(struct hv_driver *drv, guid_t *guid)
 {
 	struct vmbus_dynid *dynid;
@@ -861,7 +891,7 @@ static int vmbus_dma_configure(struct device *child_device)
 	 * On x86/x64 coherence is assumed and these calls have no effect.
 	 */
 	hv_setup_dma_ops(child_device,
-		device_get_dma_attr(hv_dev) == DEV_DMA_COHERENT);
+		device_get_dma_attr(vmbus_root_device) == DEV_DMA_COHERENT);
 	return 0;
 }
 
@@ -1921,7 +1951,8 @@ static const struct kobj_type vmbus_chan_ktype = {
  * ring for userspace to use.
  * Note: Race conditions can happen with userspace and it is not encouraged to create new
  * use-cases for this. This was added to maintain backward compatibility, while solving
- * one of the race conditions in uio_hv_generic while creating sysfs.
+ * one of the race conditions in uio_hv_generic while creating sysfs. See comments with
+ * vmbus_add_dynid() and vmbus_device_register().
  *
  * Returns 0 on success or error code on failure.
  */
@@ -2037,7 +2068,7 @@ int vmbus_device_register(struct hv_device *child_device_obj)
 		     &child_device_obj->channel->offermsg.offer.if_instance);
 
 	child_device_obj->device.bus = &hv_bus;
-	child_device_obj->device.parent = hv_dev;
+	child_device_obj->device.parent = vmbus_root_device;
 	child_device_obj->device.release = vmbus_device_release;
 
 	child_device_obj->device.dma_parms = &child_device_obj->dma_parms;
@@ -2055,6 +2086,20 @@ int vmbus_device_register(struct hv_device *child_device_obj)
 		return ret;
 	}
 
+	/*
+	 * If device_register() found a driver to assign to the device, the
+	 * driver's probe function has already run at this point. If that
+	 * probe function accesses or operates on the "channels" subdirectory
+	 * in sysfs, those operations will have failed because the "channels"
+	 * subdirectory doesn't exist until the code below runs. Or if the
+	 * probe function creates a /dev entry, a user space program could
+	 * find and open the /dev entry, and then create a race by accessing
+	 * the "channels" subdirectory while the creation steps are in progress
+	 * here. The race can't result in a kernel failure, but the user space
+	 * program may get an error in accessing "channels" or its
+	 * subdirectories. See also comments with vmbus_add_dynid() about a
+	 * related race condition.
+	 */
 	child_device_obj->channels_kset = kset_create_and_add("channels",
 							      NULL, kobj);
 	if (!child_device_obj->channels_kset) {
@@ -2412,7 +2457,7 @@ static int vmbus_acpi_add(struct platform_device *pdev)
 	struct acpi_device *ancestor;
 	struct acpi_device *device = ACPI_COMPANION(&pdev->dev);
 
-	hv_dev = &device->dev;
+	vmbus_root_device = &device->dev;
 
 	/*
 	 * Older versions of Hyper-V for ARM64 fail to include the _CCA
@@ -2465,6 +2510,31 @@ static int vmbus_acpi_add(struct platform_device *pdev)
 }
 #endif
 
+static int vmbus_set_irq(struct platform_device *pdev)
+{
+	struct irq_data *data;
+	int irq;
+	irq_hw_number_t hwirq;
+
+	irq = platform_get_irq(pdev, 0);
+	/* platform_get_irq() may not return 0. */
+	if (irq < 0)
+		return irq;
+
+	data = irq_get_irq_data(irq);
+	if (!data) {
+		pr_err("No interrupt data for VMBus virq %d\n", irq);
+		return -ENODEV;
+	}
+	hwirq = irqd_to_hwirq(data);
+
+	vmbus_irq = irq;
+	vmbus_interrupt = hwirq;
+	pr_debug("VMBus virq %d, hwirq %d\n", vmbus_irq, vmbus_interrupt);
+
+	return 0;
+}
+
 static int vmbus_device_add(struct platform_device *pdev)
 {
 	struct resource **cur_res = &hyperv_mmio;
@@ -2473,12 +2543,17 @@ static int vmbus_device_add(struct platform_device *pdev)
 	struct device_node *np = pdev->dev.of_node;
 	int ret;
 
-	hv_dev = &pdev->dev;
+	vmbus_root_device = &pdev->dev;
 
 	ret = of_range_parser_init(&parser, np);
 	if (ret)
 		return ret;
 
+	if (!__is_defined(HYPERVISOR_CALLBACK_VECTOR))
+		ret = vmbus_set_irq(pdev);
+	if (ret)
+		return ret;
+
 	for_each_of_range(&parser, &range) {
 		struct resource *res;
 
@@ -2786,7 +2861,7 @@ static int __init hv_acpi_init(void)
 	if (ret)
 		return ret;
 
-	if (!hv_dev) {
+	if (!vmbus_root_device) {
 		ret = -ENODEV;
 		goto cleanup;
 	}
@@ -2817,7 +2892,7 @@ static int __init hv_acpi_init(void)
 
 cleanup:
 	platform_driver_unregister(&vmbus_platform_driver);
-	hv_dev = NULL;
+	vmbus_root_device = NULL;
 	return ret;
 }