From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Date: Tue, 22 Jan 2019 10:39:21 -0800
Subject: driver core: Probe devices asynchronously instead of the driver
Patch-Mainline: 5.1-rc1
References: bsc#1106383
Git-commit: ef0ff68351be4fd83bec2d797f0efdc0174a55a4

Probe devices asynchronously instead of the driver. This results in us
seeing the same behavior if the device is registered before the driver or
after. This way we can avoid serializing the initialization should the
driver not be loaded until after the devices have already been added.

The motivation behind this is that if we have a set of devices that
take a significant amount of time to load we can greatly reduce the time to
load by processing them in parallel instead of one at a time. In addition,
each device can exist on a different node so placing a single thread on one
CPU to initialize all of the devices for a given driver can result in poor
performance on a system with multiple nodes.

This approach can reduce the time needed to scan SCSI LUNs significantly.
The only way to realize that speedup is by enabling more concurrency which
is what is achieved with this patch.

To achieve this it was necessary to add a new member "async_driver" to the
device_private structure to store the driver pointer while we wait on the
deferred probe call.

Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Hannes Reinecke <hare@suse.com>
---
 drivers/base/base.h |  2 ++
 drivers/base/bus.c  | 23 +++--------------------
 drivers/base/dd.c   | 43 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 48 insertions(+), 20 deletions(-)

diff --git a/drivers/base/base.h b/drivers/base/base.h
index d13cb25d94ea..bef4256f8bca 100644
--- a/drivers/base/base.h
+++ b/drivers/base/base.h
@@ -63,6 +63,7 @@ struct driver_private {
  *	binding of drivers which were unable to get all the resources needed by
  *	the device; typically because it depends on another driver getting
  *	probed first.
+ * @async_driver - pointer to device driver awaiting probe via async_probe
  * @device - pointer back to the struct device that this structure is
  * associated with.
  * @dead - This device is currently either in the process of or has been
@@ -77,6 +78,7 @@ struct device_private {
 	struct klist_node knode_driver;
 	struct klist_node knode_bus;
 	struct list_head deferred_probe;
+	struct device_driver *async_driver;
 	struct device *device;
 	u8 dead:1;
 };
diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index d1770c96f944..19b704edda33 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -649,17 +649,6 @@ static ssize_t uevent_store(struct device_driver *drv, const char *buf,
 }
 static DRIVER_ATTR_WO(uevent);
 
-static void driver_attach_async(void *_drv, async_cookie_t cookie)
-{
-	struct device_driver *drv = _drv;
-	int ret;
-
-	ret = driver_attach(drv);
-
-	pr_debug("bus: '%s': driver %s async attach completed: %d\n",
-		 drv->bus->name, drv->name, ret);
-}
-
 /**
  * bus_add_driver - Add a driver to the bus.
  * @drv: driver.
@@ -692,15 +681,9 @@ int bus_add_driver(struct device_driver *drv)
 
 	klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);
 	if (drv->bus->p->drivers_autoprobe) {
-		if (driver_allows_async_probing(drv)) {
-			pr_debug("bus: '%s': probing driver %s asynchronously\n",
-				drv->bus->name, drv->name);
-			async_schedule(driver_attach_async, drv);
-		} else {
-			error = driver_attach(drv);
-			if (error)
-				goto out_unregister;
-		}
+		error = driver_attach(drv);
+		if (error)
+			goto out_unregister;
 	}
 	module_add_driver(drv->owner, drv);
 
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 56ed47aac0ea..61cc30daa164 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -787,6 +787,30 @@ int device_driver_attach(struct device_driver *drv, struct device *dev)
 	return ret;
 }
 
+static void __driver_attach_async_helper(void *_dev, async_cookie_t cookie)
+{
+	struct device *dev = _dev;
+	struct device_driver *drv;
+	int ret = 0;
+
+	__device_driver_lock(dev, dev->parent);
+
+	drv = dev->p->async_driver;
+
+	/*
+	 * If device has been removed or someone has already successfully
+	 * bound a driver before us just skip the driver probe call.
+	 */
+	if (!dev->p->dead && !dev->driver)
+		ret = driver_probe_device(drv, dev);
+
+	__device_driver_unlock(dev, dev->parent);
+
+	dev_dbg(dev, "driver %s async attach completed: %d\n", drv->name, ret);
+
+	put_device(dev);
+}
+
 static int __driver_attach(struct device *dev, void *data)
 {
 	struct device_driver *drv = data;
@@ -814,6 +838,25 @@ static int __driver_attach(struct device *dev, void *data)
 		return ret;
 	} /* ret > 0 means positive match */
 
+	if (driver_allows_async_probing(drv)) {
+		/*
+		 * Instead of probing the device synchronously we will
+		 * probe it asynchronously to allow for more parallelism.
+		 *
+		 * We only take the device lock here in order to guarantee
+		 * that the dev->driver and async_driver fields are protected
+		 */
+		dev_dbg(dev, "probing driver %s asynchronously\n", drv->name);
+		device_lock(dev);
+		if (!dev->driver) {
+			get_device(dev);
+			dev->p->async_driver = drv;
+			async_schedule(__driver_attach_async_helper, dev);
+		}
+		device_unlock(dev);
+		return 0;
+	}
+
 	device_driver_attach(drv, dev);
 
 	return 0;
-- 
2.16.4