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driver core: Introduce device links reference counting
If device_link_add() is invoked multiple times with the same supplier and consumer combo, it will create the link on first addition and return a pointer to the already existing link on all subsequent additions. The semantics for device_link_del() are quite different, it deletes the link unconditionally, so multiple invocations are not allowed. In other words, this snippet ... struct device *dev1, *dev2; struct device_link *link1, *link2; link1 = device_link_add(dev1, dev2, 0); link2 = device_link_add(dev1, dev2, 0); device_link_del(link1); device_link_del(link2); ... causes the following crash: WARNING: CPU: 4 PID: 2686 at drivers/base/power/runtime.c:1611 pm_runtime_drop_link+0x40/0x50 [...] list_del corruption, 0000000039b800a4->prev is LIST_POISON2 (00000000ecf79852) kernel BUG at lib/list_debug.c:50! The issue isn't as arbitrary as it may seem: Imagine a device link which is added in both the supplier's and the consumer's ->probe hook. The two drivers can't just call device_link_del() in their ->remove hook without coordination. Fix by counting multiple additions and dropping the device link only when the last addition is unwound. Signed-off-by: Lukas Wunner <lukas@wunner.de> [ rjw: Subject ] Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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da997b22c4
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2 changed files with 19 additions and 8 deletions
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@ -196,8 +196,10 @@ struct device_link *device_link_add(struct device *consumer,
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}
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list_for_each_entry(link, &supplier->links.consumers, s_node)
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if (link->consumer == consumer)
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if (link->consumer == consumer) {
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kref_get(&link->kref);
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goto out;
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}
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link = kzalloc(sizeof(*link), GFP_KERNEL);
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if (!link)
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@ -222,6 +224,7 @@ struct device_link *device_link_add(struct device *consumer,
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link->consumer = consumer;
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INIT_LIST_HEAD(&link->c_node);
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link->flags = flags;
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kref_init(&link->kref);
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/* Determine the initial link state. */
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if (flags & DL_FLAG_STATELESS) {
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@ -292,8 +295,10 @@ static void __device_link_free_srcu(struct rcu_head *rhead)
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device_link_free(container_of(rhead, struct device_link, rcu_head));
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}
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static void __device_link_del(struct device_link *link)
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static void __device_link_del(struct kref *kref)
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{
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struct device_link *link = container_of(kref, struct device_link, kref);
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dev_info(link->consumer, "Dropping the link to %s\n",
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dev_name(link->supplier));
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@ -305,8 +310,10 @@ static void __device_link_del(struct device_link *link)
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call_srcu(&device_links_srcu, &link->rcu_head, __device_link_free_srcu);
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}
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#else /* !CONFIG_SRCU */
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static void __device_link_del(struct device_link *link)
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static void __device_link_del(struct kref *kref)
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{
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struct device_link *link = container_of(kref, struct device_link, kref);
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dev_info(link->consumer, "Dropping the link to %s\n",
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dev_name(link->supplier));
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@ -324,13 +331,15 @@ static void __device_link_del(struct device_link *link)
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* @link: Device link to delete.
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*
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* The caller must ensure proper synchronization of this function with runtime
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* PM.
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* PM. If the link was added multiple times, it needs to be deleted as often.
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* Care is required for hotplugged devices: Their links are purged on removal
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* and calling device_link_del() is then no longer allowed.
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*/
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void device_link_del(struct device_link *link)
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{
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device_links_write_lock();
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device_pm_lock();
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__device_link_del(link);
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kref_put(&link->kref, __device_link_del);
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device_pm_unlock();
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device_links_write_unlock();
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}
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@ -444,7 +453,7 @@ static void __device_links_no_driver(struct device *dev)
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continue;
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if (link->flags & DL_FLAG_AUTOREMOVE)
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__device_link_del(link);
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kref_put(&link->kref, __device_link_del);
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else if (link->status != DL_STATE_SUPPLIER_UNBIND)
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WRITE_ONCE(link->status, DL_STATE_AVAILABLE);
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}
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@ -597,13 +606,13 @@ static void device_links_purge(struct device *dev)
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list_for_each_entry_safe_reverse(link, ln, &dev->links.suppliers, c_node) {
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WARN_ON(link->status == DL_STATE_ACTIVE);
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__device_link_del(link);
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__device_link_del(&link->kref);
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}
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list_for_each_entry_safe_reverse(link, ln, &dev->links.consumers, s_node) {
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WARN_ON(link->status != DL_STATE_DORMANT &&
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link->status != DL_STATE_NONE);
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__device_link_del(link);
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__device_link_del(&link->kref);
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}
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device_links_write_unlock();
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@ -769,6 +769,7 @@ enum device_link_state {
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* @status: The state of the link (with respect to the presence of drivers).
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* @flags: Link flags.
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* @rpm_active: Whether or not the consumer device is runtime-PM-active.
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* @kref: Count repeated addition of the same link.
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* @rcu_head: An RCU head to use for deferred execution of SRCU callbacks.
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*/
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struct device_link {
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@ -779,6 +780,7 @@ struct device_link {
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enum device_link_state status;
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u32 flags;
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bool rpm_active;
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struct kref kref;
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#ifdef CONFIG_SRCU
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struct rcu_head rcu_head;
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#endif
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