[RFC PATCH 2/6] Improve ability to perform async shutdown in parallel

[David Jeffery <djeffery@redhat.com>]

Expands the async shutdown implementation to allow more cases of parallel
async shutdown. A field is added so that a device under async shutdown can
mark its parent as busy due to the async shutdown. A busy parent on reaching
the head of the shutdown list gets stored and flags its own parent as busy.

Once the async shutdown operations are completed, the stored parents are
returned to the shutdown list and shut down in an order maintaining their
parent-child ordering. Unlike the minimal implementation, this allows more
end nodes of the device tree to be under async shutdown in parallel.

A cap on the number of async shutdown devices is still enforced, though not
required and could be removed if desired.

Signed-off-by: David Jeffery <djeffery@redhat.com>
Tested-by:     Laurence Oberman <loberman@redhat.com>

---
 drivers/base/base.h |  1 +
 drivers/base/core.c | 71 ++++++++++++++++++++++++++++++++-------------
 2 files changed, 52 insertions(+), 20 deletions(-)

diff --git a/drivers/base/base.h b/drivers/base/base.h
index eb4c0ace9242..954008bd39e5 100644
--- a/drivers/base/base.h
+++ b/drivers/base/base.h
@@ -116,6 +116,7 @@ struct device_private {
 	char *deferred_probe_reason;
 	struct device *device;
 	u8 dead:1;
+	u8 child_shutdown:1;
 };
 #define to_device_private_parent(obj)	\
 	container_of(obj, struct device_private, knode_parent)
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 5bc2282c00cd..e88d418bf0fd 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -4720,9 +4720,10 @@ int device_change_owner(struct device *dev, kuid_t kuid, kgid_t kgid)
 EXPORT_SYMBOL_GPL(device_change_owner);
 
 
-#define MAX_ASYNC_SHUTDOWNS 32
+#define MAX_ASYNC_SHUTDOWNS 256
 static int async_shutdown_count;
 static LIST_HEAD(async_shutdown_list);
+static LIST_HEAD(async_delayed_list);
 
 /**
  * If a device has a child busy with an async shutdown or there are too many
@@ -4730,15 +4731,15 @@ static LIST_HEAD(async_shutdown_list);
  */
 static bool may_shutdown_device(struct device *dev)
 {
-	struct device *tmp;
-
-	if (async_shutdown_count >= MAX_ASYNC_SHUTDOWNS)
+	if (dev->p->child_shutdown) {
+		if (list_empty(&async_shutdown_list)) {
+			dev_err(dev, "child_shutdown set but no children? Clearing\n");
+			dev->p->child_shutdown = 0;
+			return true;
+		}
 		return false;
-
-	list_for_each_entry(tmp, &async_shutdown_list, kobj.entry) {
-		if (tmp->parent == dev)
-			return false;
 	}
+
 	return true;
 }
 
@@ -4753,6 +4754,9 @@ static void async_shutdown_start(struct device *dev, void (*callback) (struct de
 	(*callback)(dev);
 	list_add_tail(&dev->kobj.entry, &async_shutdown_list);
 	async_shutdown_count++;
+
+	if (dev->parent)
+		dev->parent->p->child_shutdown = 1;
 }
 
 /**
@@ -4760,7 +4764,7 @@ static void async_shutdown_start(struct device *dev, void (*callback) (struct de
  */
 static void wait_for_active_async_shutdown(void)
 {
-	struct device *dev, *parent;
+	struct device *dev, *parent, *tmp;
 
         while (!list_empty(&async_shutdown_list)) {
                 dev = list_entry(async_shutdown_list.next, struct device,
@@ -4787,15 +4791,29 @@ static void wait_for_active_async_shutdown(void)
 			dev->driver->async_shutdown_end(dev);
 		}
                 device_unlock(dev);
-                if (parent)
-                        device_unlock(parent);
-
+                if (parent) {
+			tmp = parent;
+			do {
+				tmp->p->child_shutdown = 0;
+				device_unlock(tmp);
+
+				tmp = tmp->parent;
+				if (!tmp || !tmp->p->child_shutdown)
+					break;
+				device_lock(tmp);
+			} while (1);
+		}
                 put_device(dev);
                 put_device(parent);
         }
 	if (initcall_debug)
 		printk(KERN_INFO "device shutdown: waited for %d async shutdown callbacks\n", async_shutdown_count);
+
 	async_shutdown_count = 0;
+	spin_lock(&devices_kset->list_lock);
+	list_splice_tail_init(&async_delayed_list, &devices_kset->list);
+	spin_unlock(&devices_kset->list_lock);
+
 }
 
 /**
@@ -4810,7 +4828,7 @@ void device_shutdown(void)
 	device_block_probing();
 
 	cpufreq_suspend();
-
+restart:
 	spin_lock(&devices_kset->list_lock);
 	/*
 	 * Walk the devices list backward, shutting down each in turn.
@@ -4832,12 +4850,15 @@ void device_shutdown(void)
 		get_device(dev);
 
                 if (!may_shutdown_device(dev)) {
+			list_move(&dev->kobj.entry, &async_delayed_list);
+			if (parent) {
+				device_lock(parent);
+				parent->p->child_shutdown = 1;
+				device_unlock(parent);
+			}
+
 			put_device(dev);
 			put_device(parent);
-
-			spin_unlock(&devices_kset->list_lock);
-			wait_for_active_async_shutdown();
-			spin_lock(&devices_kset->list_lock);
 			continue;
 		}
 
@@ -4863,14 +4884,16 @@ void device_shutdown(void)
 			dev->class->shutdown_pre(dev);
 		}
 		if (dev->bus && dev->bus->async_shutdown_start) {
-			async_shutdown_start(dev, dev->bus->async_shutdown_start);
+			async_shutdown_start(dev,
+					     dev->bus->async_shutdown_start);
 			async_busy = true;
 		} else if (dev->bus && dev->bus->shutdown) {
 			if (initcall_debug)
 				dev_info(dev, "shutdown\n");
 			dev->bus->shutdown(dev);
 		} else if (dev->driver && dev->driver->async_shutdown_start) {
-			async_shutdown_start(dev, dev->driver->async_shutdown_start);
+			async_shutdown_start(dev,
+					     dev->driver->async_shutdown_start);
 			async_busy = true;
 		} else if (dev->driver && dev->driver->shutdown) {
 			if (initcall_debug)
@@ -4891,14 +4914,22 @@ void device_shutdown(void)
 			put_device(parent);
 		}
 
+		if (async_shutdown_count == MAX_ASYNC_SHUTDOWNS)
+			wait_for_active_async_shutdown();
+
 		spin_lock(&devices_kset->list_lock);
 	}
 	spin_unlock(&devices_kset->list_lock);
 	/*
-	 * Wait for any async shutdown still running.
+	 * Wait for any async shutdown still running, then restart the loop
+	 * if the list is no longer empty from delayed entries returning to
+	 * the list.
 	 */
 	if (!list_empty(&async_shutdown_list))
 		wait_for_active_async_shutdown();
+
+	if(!list_empty(&devices_kset->list))
+		goto restart;
 }
 
 /*
-- 
2.43.0