[PATCH v3] driver core: Allow device link operations inside sync_state()

From: Saravana Kannan
Date: Thu Nov 14 2019 - 17:24:03 EST


Some sync_state() implementations might need to call APIs that in turn
make calls to device link APIs. So, do the sync_state() callbacks
without holding the device link lock.

Signed-off-by: Saravana Kannan <saravanak@xxxxxxxxxx>
---
drivers/base/core.c | 80 ++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 72 insertions(+), 8 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index e6d3e6d485da..9a88bcfd5d33 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -695,7 +695,26 @@ int device_links_check_suppliers(struct device *dev)
return ret;
}

-static void __device_links_supplier_sync_state(struct device *dev)
+/**
+ * __device_links_queue_sync_state - Queue a device for sync_state() callback
+ * @dev: Device to call sync_state() on
+ * @list: List head to queue the @dev on
+ *
+ * Queues a device for a sync_state() callback when the device links write lock
+ * isn't held. This allows the sync_state() execution flow to use device links
+ * APIs. The caller must ensure this function is called with
+ * device_links_write_lock() held.
+ *
+ * This function does a get_device() to make sure the device is not freed while
+ * on this list.
+ *
+ * So the caller must also ensure that device_links_flush_sync_list() is called
+ * as soon as the caller releases device_links_write_lock(). This is necessary
+ * to make sure the sync_state() is called in a timely fashion and the
+ * put_device() is called on this device.
+ */
+static void __device_links_queue_sync_state(struct device *dev,
+ struct list_head *list)
{
struct device_link *link;

@@ -709,12 +728,46 @@ static void __device_links_supplier_sync_state(struct device *dev)
return;
}

- if (dev->bus->sync_state)
- dev->bus->sync_state(dev);
- else if (dev->driver && dev->driver->sync_state)
- dev->driver->sync_state(dev);
-
+ /*
+ * Set the flag here to avoid adding the same device to a list more
+ * than once. This can happen if new consumers get added to the device
+ * and probed before the list is flushed.
+ */
dev->state_synced = true;
+
+ if (list_empty(&dev->links.defer_sync)) {
+ get_device(dev);
+ list_add_tail(&dev->links.defer_sync, list);
+ } else {
+ WARN_ON(1);
+ }
+}
+
+/**
+ * device_links_flush_sync_list - Call sync_state() on a list of devices
+ * @list: List of devices to call sync_state() on
+ *
+ * Calls sync_state() on all the devices that have been queued for it. This
+ * function is used in conjunction with __device_links_queue_sync_state().
+ */
+static void device_links_flush_sync_list(struct list_head *list)
+{
+ struct device *dev, *tmp;
+
+ list_for_each_entry_safe(dev, tmp, list, links.defer_sync) {
+ list_del_init(&dev->links.defer_sync);
+
+ device_lock(dev);
+
+ if (dev->bus->sync_state)
+ dev->bus->sync_state(dev);
+ else if (dev->driver && dev->driver->sync_state)
+ dev->driver->sync_state(dev);
+
+ device_unlock(dev);
+
+ put_device(dev);
+ }
}

void device_links_supplier_sync_state_pause(void)
@@ -727,6 +780,7 @@ void device_links_supplier_sync_state_pause(void)
void device_links_supplier_sync_state_resume(void)
{
struct device *dev, *tmp;
+ LIST_HEAD(sync_list);

device_links_write_lock();
if (!defer_sync_state_count) {
@@ -738,11 +792,17 @@ void device_links_supplier_sync_state_resume(void)
goto out;

list_for_each_entry_safe(dev, tmp, &deferred_sync, links.defer_sync) {
- __device_links_supplier_sync_state(dev);
+ /*
+ * Delete from deferred_sync list before queuing it to
+ * sync_list because defer_sync is used for both lists.
+ */
list_del_init(&dev->links.defer_sync);
+ __device_links_queue_sync_state(dev, &sync_list);
}
out:
device_links_write_unlock();
+
+ device_links_flush_sync_list(&sync_list);
}

static int sync_state_resume_initcall(void)
@@ -772,6 +832,7 @@ static void __device_links_supplier_defer_sync(struct device *sup)
void device_links_driver_bound(struct device *dev)
{
struct device_link *link;
+ LIST_HEAD(sync_list);

/*
* If a device probes successfully, it's expected to have created all
@@ -815,12 +876,15 @@ void device_links_driver_bound(struct device *dev)
if (defer_sync_state_count)
__device_links_supplier_defer_sync(link->supplier);
else
- __device_links_supplier_sync_state(link->supplier);
+ __device_links_queue_sync_state(link->supplier,
+ &sync_list);
}

dev->links.status = DL_DEV_DRIVER_BOUND;

device_links_write_unlock();
+
+ device_links_flush_sync_list(&sync_list);
}

static void device_link_drop_managed(struct device_link *link)
--
2.24.0.432.g9d3f5f5b63-goog