From ead18c23c263374ed098a7d955b29b4a466d4573 Mon Sep 17 00:00:00 2001 From: Lukas Wunner Date: Sat, 10 Feb 2018 19:27:12 +0100 Subject: 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 [ rjw: Subject ] Signed-off-by: Rafael J. Wysocki --- drivers/base/core.c | 25 +++++++++++++++++-------- 1 file changed, 17 insertions(+), 8 deletions(-) (limited to 'drivers/base/core.c') diff --git a/drivers/base/core.c b/drivers/base/core.c index 5847364f25d9..b610816eb887 100644 --- a/drivers/base/core.c +++ b/drivers/base/core.c @@ -196,8 +196,10 @@ struct device_link *device_link_add(struct device *consumer, } list_for_each_entry(link, &supplier->links.consumers, s_node) - if (link->consumer == consumer) + if (link->consumer == consumer) { + kref_get(&link->kref); goto out; + } link = kzalloc(sizeof(*link), GFP_KERNEL); if (!link) @@ -222,6 +224,7 @@ struct device_link *device_link_add(struct device *consumer, link->consumer = consumer; INIT_LIST_HEAD(&link->c_node); link->flags = flags; + kref_init(&link->kref); /* Determine the initial link state. */ if (flags & DL_FLAG_STATELESS) { @@ -292,8 +295,10 @@ static void __device_link_free_srcu(struct rcu_head *rhead) device_link_free(container_of(rhead, struct device_link, rcu_head)); } -static void __device_link_del(struct device_link *link) +static void __device_link_del(struct kref *kref) { + struct device_link *link = container_of(kref, struct device_link, kref); + dev_info(link->consumer, "Dropping the link to %s\n", dev_name(link->supplier)); @@ -305,8 +310,10 @@ static void __device_link_del(struct device_link *link) call_srcu(&device_links_srcu, &link->rcu_head, __device_link_free_srcu); } #else /* !CONFIG_SRCU */ -static void __device_link_del(struct device_link *link) +static void __device_link_del(struct kref *kref) { + struct device_link *link = container_of(kref, struct device_link, kref); + dev_info(link->consumer, "Dropping the link to %s\n", dev_name(link->supplier)); @@ -324,13 +331,15 @@ static void __device_link_del(struct device_link *link) * @link: Device link to delete. * * The caller must ensure proper synchronization of this function with runtime - * PM. + * PM. If the link was added multiple times, it needs to be deleted as often. + * Care is required for hotplugged devices: Their links are purged on removal + * and calling device_link_del() is then no longer allowed. */ void device_link_del(struct device_link *link) { device_links_write_lock(); device_pm_lock(); - __device_link_del(link); + kref_put(&link->kref, __device_link_del); device_pm_unlock(); device_links_write_unlock(); } @@ -444,7 +453,7 @@ static void __device_links_no_driver(struct device *dev) continue; if (link->flags & DL_FLAG_AUTOREMOVE) - __device_link_del(link); + kref_put(&link->kref, __device_link_del); else if (link->status != DL_STATE_SUPPLIER_UNBIND) WRITE_ONCE(link->status, DL_STATE_AVAILABLE); } @@ -597,13 +606,13 @@ static void device_links_purge(struct device *dev) list_for_each_entry_safe_reverse(link, ln, &dev->links.suppliers, c_node) { WARN_ON(link->status == DL_STATE_ACTIVE); - __device_link_del(link); + __device_link_del(&link->kref); } list_for_each_entry_safe_reverse(link, ln, &dev->links.consumers, s_node) { WARN_ON(link->status != DL_STATE_DORMANT && link->status != DL_STATE_NONE); - __device_link_del(link); + __device_link_del(&link->kref); } device_links_write_unlock(); -- cgit