Commit 21c27f06 authored by Saravana Kannan's avatar Saravana Kannan Committed by Greg Kroah-Hartman
Browse files

driver core: Fix SYNC_STATE_ONLY device link implementation 



When SYNC_STATE_ONLY support was added in commit 05ef983e ("driver
core: Add device link support for SYNC_STATE_ONLY flag"),
device_link_add() incorrectly skipped adding the new SYNC_STATE_ONLY
device link to the supplier's and consumer's "device link" list.

This causes multiple issues:
- The device link is lost forever from driver core if the caller
  didn't keep track of it (caller typically isn't expected to). This is
  a memory leak.
- The device link is also never visible to any other code path after
  device_link_add() returns.

If we fix the "device link" list handling, that exposes a bunch of
issues.

1. The device link "status" state management code rightfully doesn't
handle the case where a DL_FLAG_MANAGED device link exists between a
supplier and consumer, but the consumer manages to probe successfully
before the supplier. The addition of DL_FLAG_SYNC_STATE_ONLY links break
this assumption. This causes device_links_driver_bound() to throw a
warning when this happens.

Since DL_FLAG_SYNC_STATE_ONLY device links are mainly used for creating
proxy device links for child device dependencies and aren't useful once
the consumer device probes successfully, this patch just deletes
DL_FLAG_SYNC_STATE_ONLY device links once its consumer device probes.
This way, we avoid the warning, free up some memory and avoid
complicating the device links "status" state management code.

2. Creating a DL_FLAG_STATELESS device link between two devices that
already have a DL_FLAG_SYNC_STATE_ONLY device link will result in the
DL_FLAG_STATELESS flag not getting set correctly. This patch also fixes
this.

Lastly, this patch also fixes minor whitespace issues.

Cc: stable@vger.kernel.org
Fixes: 05ef983e ("driver core: Add device link support for SYNC_STATE_ONLY flag")
Signed-off-by: default avatarSaravana Kannan <saravanak@google.com>
Reviewed-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/r/20200519063000.128819-1-saravanak@google.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 2ef96a5b

drivers/base/core.c

+39 −22
Original line number Diff line number Diff line
@@ -360,14 +360,13 @@ struct device_link *device_link_add(struct device *consumer, 


		if (flags & DL_FLAG_STATELESS) {

			kref_get(&link->kref);

			if (link->flags & DL_FLAG_SYNC_STATE_ONLY &&

			    !(link->flags & DL_FLAG_STATELESS)) {

			link->flags |= DL_FLAG_STATELESS;

			if (link->flags & DL_FLAG_SYNC_STATE_ONLY &&

			    !(link->flags & DL_FLAG_STATELESS))

				goto reorder;

			} else {

			else

				goto out;

		}

		}



		/*

		 * If the life time of the link following from the new flags is
@@ -433,12 +432,16 @@ struct device_link *device_link_add(struct device *consumer, 
	    flags & DL_FLAG_PM_RUNTIME)

		pm_runtime_resume(supplier);



	list_add_tail_rcu(&link->s_node, &supplier->links.consumers);

	list_add_tail_rcu(&link->c_node, &consumer->links.suppliers);



	if (flags & DL_FLAG_SYNC_STATE_ONLY) {

		dev_dbg(consumer,

			"Linked as a sync state only consumer to %s\n",

			dev_name(supplier));

		goto out;

	}



reorder:

	/*

	 * Move the consumer and all of the devices depending on it to the end
@@ -449,9 +452,6 @@ reorder: 
	 */

	device_reorder_to_tail(consumer, NULL);



	list_add_tail_rcu(&link->s_node, &supplier->links.consumers);

	list_add_tail_rcu(&link->c_node, &consumer->links.suppliers);



	dev_dbg(consumer, "Linked as a consumer to %s\n", dev_name(supplier));



out:
@@ -829,6 +829,13 @@ static void __device_links_supplier_defer_sync(struct device *sup) 
		list_add_tail(&sup->links.defer_sync, &deferred_sync);

}



static void device_link_drop_managed(struct device_link *link)

{

	link->flags &= ~DL_FLAG_MANAGED;

	WRITE_ONCE(link->status, DL_STATE_NONE);

	kref_put(&link->kref, __device_link_del);

}



/**

 * device_links_driver_bound - Update device links after probing its driver.

 * @dev: Device to update the links for.
@@ -842,7 +849,7 @@ static void __device_links_supplier_defer_sync(struct device *sup) 
 */

void device_links_driver_bound(struct device *dev)

{

	struct device_link *link;

	struct device_link *link, *ln;

	LIST_HEAD(sync_list);



	/*
@@ -882,18 +889,35 @@ void device_links_driver_bound(struct device *dev) 
	else

		__device_links_queue_sync_state(dev, &sync_list);



	list_for_each_entry(link, &dev->links.suppliers, c_node) {

	list_for_each_entry_safe(link, ln, &dev->links.suppliers, c_node) {

		struct device *supplier;



		if (!(link->flags & DL_FLAG_MANAGED))

			continue;



		supplier = link->supplier;

		if (link->flags & DL_FLAG_SYNC_STATE_ONLY) {

			/*

			 * When DL_FLAG_SYNC_STATE_ONLY is set, it means no

			 * other DL_MANAGED_LINK_FLAGS have been set. So, it's

			 * save to drop the managed link completely.

			 */

			device_link_drop_managed(link);

		} else {

			WARN_ON(link->status != DL_STATE_CONSUMER_PROBE);

			WRITE_ONCE(link->status, DL_STATE_ACTIVE);

		}



		/*

		 * This needs to be done even for the deleted

		 * DL_FLAG_SYNC_STATE_ONLY device link in case it was the last

		 * device link that was preventing the supplier from getting a

		 * sync_state() call.

		 */

		if (defer_sync_state_count)

			__device_links_supplier_defer_sync(link->supplier);

			__device_links_supplier_defer_sync(supplier);

		else

			__device_links_queue_sync_state(link->supplier,

							&sync_list);

			__device_links_queue_sync_state(supplier, &sync_list);

	}



	dev->links.status = DL_DEV_DRIVER_BOUND;
@@ -903,13 +927,6 @@ void device_links_driver_bound(struct device *dev) 
	device_links_flush_sync_list(&sync_list, dev);

}



static void device_link_drop_managed(struct device_link *link)

{

	link->flags &= ~DL_FLAG_MANAGED;

	WRITE_ONCE(link->status, DL_STATE_NONE);

	kref_put(&link->kref, __device_link_del);

}



/**

 * __device_links_no_driver - Update links of a device without a driver.

 * @dev: Device without a drvier.

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