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Subject[PATCH v2] driver core: Fix SYNC_STATE_ONLY device link implementation
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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>
---
drivers/base/core.c | 61 +++++++++++++++++++++++++++++----------------
1 file changed, 39 insertions(+), 22 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 84c569726d75..f804e561e0a2 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -363,13 +363,12 @@ 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;
- }
}

/*
@@ -436,12 +435,16 @@ 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
@@ -452,12 +455,9 @@ struct device_link *device_link_add(struct device *consumer,
*/
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();

@@ -832,6 +832,13 @@ 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.
@@ -845,7 +852,7 @@ 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);

/*
@@ -885,18 +892,35 @@ 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;
@@ -906,13 +930,6 @@ 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.
--
2.26.2.761.g0e0b3e54be-goog
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