[PATCH] driver core: fix async device shutdown hang

[Stuart Hayes]

Modify device_shutdown() so that supplier devices do not wait for
consumer devices to be shut down first when the devlink is sync state
only, since the consumer is not dependent on the supplier in this case.

Without this change, a circular dependency could hang the system.

Fixes: 8064952c6504 ("driver core: shut down devices asynchronously")

Signed-off-by: Stuart Hayes <stuart.w.hayes at gmail.com>
---
The patch this fixes is in driver-core-next and linux-next.

Please let me know if this needs to be a V2 or if it needs anything
else... it is the identical patch I sent in yesterday, except I added
a "Fixes:" tag and the comments.  Thank you for the help!

 drivers/base/core.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index b69b82da8837..76513e360496 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -4898,8 +4898,16 @@ void device_shutdown(void)
 
 		idx = device_links_read_lock();
 		list_for_each_entry_rcu(link, &dev->links.suppliers, c_node,
-				device_links_read_lock_held())
+				device_links_read_lock_held()) {
+			/*
+			 * sync_state_only suppliers don't need to wait,
+			 * aren't reordered on devices_kset, so making them
+			 * wait could result in a hang
+			 */
+			if (device_link_flag_is_sync_state_only(link->flags))
+				continue;
 			link->supplier->p->shutdown_after = cookie;
+		}
 		device_links_read_unlock(idx);
 		put_device(dev);
 
-- 
2.39.3