driver core: add test of driver remove calls during probe

In recent discussions on ksummit-discuss[1], it was suggested to do a
sequence of probe, remove, probe for testing driver remove paths. This
adds a kconfig option for said test.

[1] https://lists.linuxfoundation.org/pipermail/ksummit-discuss/2016-August/003459.html

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/Kconfig

@@ -212,6 +212,16 @@ config DEBUG_DEVRES
 
 	  If you are unsure about this, Say N here.
 
+config DEBUG_TEST_DRIVER_REMOVE
+	bool "Test driver remove calls during probe"
+	depends on DEBUG_KERNEL
+	help
+	  Say Y here if you want the Driver core to test driver remove functions
+	  by calling probe, remove, probe. This tests the remove path without
+	  having to unbind the driver or unload the driver module.
+
+	  If you are unsure about this, say N here.
+
 config SYS_HYPERVISOR
 	bool
 	default n

drivers/base/dd.c

@@ -329,6 +329,7 @@ static int really_probe(struct device *dev, struct device_driver *drv)
 {
 	int ret = -EPROBE_DEFER;
 	int local_trigger_count = atomic_read(&deferred_trigger_count);
+	bool test_remove = IS_ENABLED(CONFIG_DEBUG_TEST_DRIVER_REMOVE);
 
 	if (defer_all_probes) {
 		/*
@@ -346,6 +347,7 @@ static int really_probe(struct device *dev, struct device_driver *drv)
 		 drv->bus->name, __func__, drv->name, dev_name(dev));
 	WARN_ON(!list_empty(&dev->devres_head));
 
+re_probe:
 	dev->driver = drv;
 
 	/* If using pinctrl, bind pins now before probing */
@@ -383,6 +385,25 @@ static int really_probe(struct device *dev, struct device_driver *drv)
 			goto probe_failed;
 	}
 
+	if (test_remove) {
+		test_remove = false;
+
+		if (dev->bus && dev->bus->remove)
+			dev->bus->remove(dev);
+		else if (drv->remove)
+			drv->remove(dev);
+
+		devres_release_all(dev);
+		driver_sysfs_remove(dev);
+		dev->driver = NULL;
+		dev_set_drvdata(dev, NULL);
+		if (dev->pm_domain && dev->pm_domain->dismiss)
+			dev->pm_domain->dismiss(dev);
+		pm_runtime_reinit(dev);
+
+		goto re_probe;
+	}
+
 	pinctrl_init_done(dev);
 
 	if (dev->pm_domain && dev->pm_domain->sync)