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 --- include/linux/device.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include/linux/device.h') diff --git a/include/linux/device.h b/include/linux/device.h index b093405ed525..abf952c82c6d 100644 --- a/include/linux/device.h +++ b/include/linux/device.h @@ -769,6 +769,7 @@ enum device_link_state { * @status: The state of the link (with respect to the presence of drivers). * @flags: Link flags. * @rpm_active: Whether or not the consumer device is runtime-PM-active. + * @kref: Count repeated addition of the same link. * @rcu_head: An RCU head to use for deferred execution of SRCU callbacks. */ struct device_link { @@ -779,6 +780,7 @@ struct device_link { enum device_link_state status; u32 flags; bool rpm_active; + struct kref kref; #ifdef CONFIG_SRCU struct rcu_head rcu_head; #endif -- cgit v1.2.3-55-g7522