driver core: Fix SYNC_STATE_ONLY device link implementation

When SYNC_STATE_ONLY support was added in commit 05ef983e0d65 ("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: 05ef983e0d65 ("driver core: Add device link support for SYNC_STATE_ONLY flag")
Signed-off-by: Saravana Kannan <saravanak@google.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/r/20200519063000.128819-1-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 073045c..4e0e430 100644 (file)
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -360,13 +360,12 @@ struct device_link *device_link_add(struct device *consumer,
 
                if (flags & DL_FLAG_STATELESS) {
                        kref_get(&link->kref);
+                       link->flags |= DL_FLAG_STATELESS;
                        if (link->flags & DL_FLAG_SYNC_STATE_ONLY &&
-                           !(link->flags & DL_FLAG_STATELESS)) {
-                               link->flags |= DL_FLAG_STATELESS;
+                           !(link->flags & DL_FLAG_STATELESS))
                                goto reorder;
-                       } else {
+                       else
                                goto out;
-                       }
                }
 
                /*
@@ -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
@@ -449,12 +452,9 @@ 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:
+out:
        device_pm_unlock();
        device_links_write_unlock();
 
@@ -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;
 
-               WARN_ON(link->status != DL_STATE_CONSUMER_PROBE);
-               WRITE_ONCE(link->status, DL_STATE_ACTIVE);
+               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.