patch "mei: amthif: fix deadlock in initialization during a reset" added to char-misc-testing

This is a note to let you know that I've just added the patch titled

mei: amthif: fix deadlock in initialization during a reset

to my char-misc git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-testing branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will be merged to the char-misc-next branch sometime soon, after it passes testing, and the merge window is open.

If you have any questions about this process, please let me know.

From: Alexander Usyskin <[email protected]>
Date: Tue, 26 Jul 2016 01:06:09 +0300
Subject: mei: amthif: fix deadlock in initialization during a reset

The device lock was unnecessary obtained in bus rescan work before the amthif client search. That causes incorrect lock ordering and task hang:
...

[88004.613213] INFO: task kworker/1:14:21832 blocked for more than 120 seconds.
...
[88004.645934] Workqueue: events mei_cl_bus_rescan_work

...

The correct lock order is
cl_bus_lock
device_lock
me_clients_rwsem

Move device_lock into amthif init function that called after me_clients_rwsem is released.

This fixes regression introduced by commit:
commit 025fb792bac3 ("mei: split amthif client init from end of clients enumeration")

---
 drivers/misc/mei/amthif.c | 12 +++++++++---
 drivers/misc/mei/bus.c    |  2 --
 2 files changed, 9 insertions(+), 5 deletions(-)

index 2222b60e9208..082462ea90c9 100644
@@ -66,8 +66,12 @@ int mei_amthif_host_init(struct mei_device *dev, struct mei_me_client *me_cl)
 	struct mei_cl *cl = &dev->iamthif_cl;
 	int ret;
 
-	if (mei_cl_is_connected(cl))
-		return 0;
+	mutex_lock(&dev->device_lock);
+
+	if (mei_cl_is_connected(cl)) {
+		ret = 0;
+		goto out;
+	}
 
 	dev->iamthif_state = MEI_IAMTHIF_IDLE;
 

@@ -76,11 +80,13 @@ int mei_amthif_host_init(struct mei_device *dev, struct mei_me_client *me_cl)
 	ret = mei_cl_link(cl);
 	if (ret < 0) {
 		dev_err(dev->dev, "amthif: failed cl_link %d\n", ret);
-		return ret;
+		goto out;
 	}
 
 	ret = mei_cl_connect(cl, me_cl, NULL);
 
+out:
+	mutex_unlock(&dev->device_lock);
 	return ret;
 }
 

index cdf13f6d2697..8cac7ef9ad0d 100644
@@ -984,12 +984,10 @@ void mei_cl_bus_rescan_work(struct work_struct *work)
 		container_of(work, struct mei_device, bus_rescan_work);
 	struct mei_me_client *me_cl;
 
-	mutex_lock(&bus->device_lock);
 	me_cl = mei_me_cl_by_uuid(bus, &mei_amthif_guid);
 	if (me_cl)
 		mei_amthif_host_init(bus, me_cl);
 	mei_me_cl_put(me_cl);
-	mutex_unlock(&bus->device_lock);
 
 	mei_cl_bus_rescan(bus);
 }

2.9.3