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Subject[PATCH v5 2/3] drivers core: prepare device_shutdown for multi-threading
Date
Do all the necessary refactoring to prepare device_shutdown() logic to
be multi-threaded.

Which includes:
1. Change the direction of traversing the list instead of going backward,
we now go forward.
2. Children are shutdown recursively for each root device from bottom-up.
3. Functions that can be multi-threaded have _task() in their name.

Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
---
drivers/base/core.c | 178 ++++++++++++++++++++++++++++++++++++--------
1 file changed, 149 insertions(+), 29 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index ed189f6d1a2f..210b619931bc 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -2102,6 +2102,59 @@ const char *device_get_devnode(struct device *dev,
return *tmp = s;
}

+/*
+ * device_children_count - device children count
+ * @parent: parent struct device.
+ *
+ * Returns number of children for this device or 0 if none.
+ */
+static int device_children_count(struct device *parent)
+{
+ struct klist_iter i;
+ int children = 0;
+
+ if (!parent->p)
+ return 0;
+
+ klist_iter_init(&parent->p->klist_children, &i);
+ while (next_device(&i))
+ children++;
+ klist_iter_exit(&i);
+
+ return children;
+}
+
+/*
+ * device_get_child_by_index - Return child using the provided index.
+ * @parent: parent struct device.
+ * @index: Index of the child, where 0 is the first child in the children list,
+ * and so on.
+ *
+ * Returns child or NULL if child with this index is not present.
+ */
+static struct device *
+device_get_child_by_index(struct device *parent, int index)
+{
+ struct klist_iter i;
+ struct device *dev = NULL, *d;
+ int child_index = 0;
+
+ if (!parent->p || index < 0)
+ return NULL;
+
+ klist_iter_init(&parent->p->klist_children, &i);
+ while ((d = next_device(&i))) {
+ if (child_index == index) {
+ dev = d;
+ break;
+ }
+ child_index++;
+ }
+ klist_iter_exit(&i);
+
+ return dev;
+}
+
/**
* device_for_each_child - device child iterator.
* @parent: parent struct device.
@@ -2794,50 +2847,117 @@ static void device_shutdown_one(struct device *dev)
put_device(dev);
}

+/*
+ * Passed as an argument to device_shutdown_child_task().
+ * child_next_index the next available child index.
+ * parent Parent device.
+ */
+struct device_shutdown_task_data {
+ atomic_t child_next_index;
+ struct device *parent;
+};
+
+static int device_shutdown_child_task(void *data);
+
+/*
+ * Shutdown device tree with root started in dev. If dev has no children
+ * simply shutdown only this device. If dev has children recursively shutdown
+ * children first, and only then the parent.
+ */
+static void device_shutdown_tree(struct device *dev)
+{
+ int children_count;
+
+ device_lock(dev);
+ children_count = device_children_count(dev);
+
+ if (children_count) {
+ struct device_shutdown_task_data tdata;
+ int i;
+
+ atomic_set(&tdata.child_next_index, 0);
+ tdata.parent = dev;
+
+ for (i = 0; i < children_count; i++) {
+ device_shutdown_child_task(&tdata);
+ }
+ }
+ device_shutdown_one(dev);
+ device_unlock(dev);
+}
+
+/*
+ * Only devices with parent are going through this function. The parent is
+ * locked and waits for all of its children to finish shutting down before
+ * calling shutdown function for itself.
+ */
+static int device_shutdown_child_task(void *data)
+{
+ struct device_shutdown_task_data *tdata = data;
+ int cidx = atomic_inc_return(&tdata->child_next_index) - 1;
+ struct device *dev = device_get_child_by_index(tdata->parent, cidx);
+
+ /* ref. counter is going to be decremented in device_shutdown_one() */
+ get_device(dev);
+ device_shutdown_tree(dev);
+ return 0;
+}
+
+/*
+ * On shutdown each root device (the one that does not have a parent) goes
+ * through this function.
+ */
+static int device_shutdown_root_task(void *data)
+{
+ struct device *dev = (struct device *)data;
+
+ device_shutdown_tree(dev);
+
+ return 0;
+}
+
/**
* device_shutdown - call ->shutdown() on each device to shutdown.
*/
void device_shutdown(void)
{
- struct device *dev, *parent;
+ struct device *dev;

- spin_lock(&devices_kset->list_lock);
- /*
- * Walk the devices list backward, shutting down each in turn.
- * Beware that device unplug events may also start pulling
- * devices offline, even as the system is shutting down.
+ /* Shutdown the root devices. The children are going to be
+ * shutdown first in device_shutdown_tree().
*/
+ spin_lock(&devices_kset->list_lock);
while (!list_empty(&devices_kset->list)) {
- dev = list_entry(devices_kset->list.prev, struct device,
- kobj.entry);
+ dev = list_entry(devices_kset->list.next, struct device,
+ kobj.entry);

- /*
- * hold reference count of device's parent to
- * prevent it from being freed because parent's
- * lock is to be held
- */
- parent = get_device(dev->parent);
- get_device(dev);
/*
* Make sure the device is off the kset list, in the
* event that dev->*->shutdown() doesn't remove it.
*/
list_del_init(&dev->kobj.entry);
- spin_unlock(&devices_kset->list_lock);

- /* hold lock to avoid race with probe/release */
- if (parent)
- device_lock(parent);
- device_lock(dev);
-
- device_shutdown_one(dev);
- device_unlock(dev);
- if (parent)
- device_unlock(parent);
-
- put_device(parent);
-
- spin_lock(&devices_kset->list_lock);
+ /* Here we start tasks for root devices only */
+ if (!dev->parent) {
+ /* Prevents devices from being freed. The counter is
+ * going to be decremented in device_shutdown_one() once
+ * this root device is shutdown.
+ */
+ get_device(dev);
+
+ /* We unlock list for performance reasons,
+ * dev->*->shutdown(), may try to take this lock to
+ * remove us from kset list. To avoid unlocking this
+ * list we could replace spin lock in:
+ * dev->kobj.kset->list_lock with a dummy one once
+ * device is locked in device_shutdown_root_task() and
+ * in device_shutdown_child_task().
+ */
+ spin_unlock(&devices_kset->list_lock);
+
+ device_shutdown_root_task(dev);
+ spin_lock(&devices_kset->list_lock);
+ }
}
spin_unlock(&devices_kset->list_lock);
}
--
2.17.0
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