Patch "usb: core: hub: hub_port_init lock controller instead of bus" has been added to the 4.4-stable tree

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

usb: core: hub: hub_port_init lock controller instead of bus

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
usb-core-hub-hub_port_init-lock-controller-instead-of-bus.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Chris Bainbridge <[email protected]>
Date: Mon, 25 Apr 2016 13:48:38 +0100
Subject: usb: core: hub: hub_port_init lock controller instead of bus

From: Chris Bainbridge <[email protected]>

commit feb26ac31a2a5cb88d86680d9a94916a6343e9e6 upstream.

The XHCI controller presents two USB buses to the system - one for USB2 and one for USB3. The hub init code (hub_port_init) is reentrant but only locks one bus per thread, leading to a race condition failure when two threads attempt to simultaneously initialise a USB2 and USB3 device:

[    8.034843] xhci_hcd 0000:00:14.0: Timeout while waiting for setup device command
[   13.183701] usb 3-3: device descriptor read/all, error -110

On a test system this failure occurred on 6% of all boots.

The call traces at the point of failure are:

Call Trace:
 [<ffffffff81b9bab7>] schedule+0x37/0x90
 [<ffffffff817da7cd>] usb_kill_urb+0x8d/0xd0
 [<ffffffff8111e5e0>] ? wake_up_atomic_t+0x30/0x30
 [<ffffffff817dafbe>] usb_start_wait_urb+0xbe/0x150
 [<ffffffff817db10c>] usb_control_msg+0xbc/0xf0
 [<ffffffff817d07de>] hub_port_init+0x51e/0xb70
 [<ffffffff817d4697>] hub_event+0x817/0x1570
 [<ffffffff810f3e6f>] process_one_work+0x1ff/0x620
 [<ffffffff810f3dcf>] ? process_one_work+0x15f/0x620
 [<ffffffff810f4684>] worker_thread+0x64/0x4b0
 [<ffffffff810f4620>] ? rescuer_thread+0x390/0x390
 [<ffffffff810fa7f5>] kthread+0x105/0x120
 [<ffffffff810fa6f0>] ? kthread_create_on_node+0x200/0x200
 [<ffffffff81ba183f>] ret_from_fork+0x3f/0x70
 [<ffffffff810fa6f0>] ? kthread_create_on_node+0x200/0x200

Call Trace:
 [<ffffffff817fd36d>] xhci_setup_device+0x53d/0xa40
 [<ffffffff817fd87e>] xhci_address_device+0xe/0x10
 [<ffffffff817d047f>] hub_port_init+0x1bf/0xb70
 [<ffffffff811247ed>] ? trace_hardirqs_on+0xd/0x10
 [<ffffffff817d4697>] hub_event+0x817/0x1570
 [<ffffffff810f3e6f>] process_one_work+0x1ff/0x620
 [<ffffffff810f3dcf>] ? process_one_work+0x15f/0x620
 [<ffffffff810f4684>] worker_thread+0x64/0x4b0
 [<ffffffff810f4620>] ? rescuer_thread+0x390/0x390
 [<ffffffff810fa7f5>] kthread+0x105/0x120
 [<ffffffff810fa6f0>] ? kthread_create_on_node+0x200/0x200
 [<ffffffff81ba183f>] ret_from_fork+0x3f/0x70
 [<ffffffff810fa6f0>] ? kthread_create_on_node+0x200/0x200

Which results from the two call chains:

hub_port_init
usb_get_device_descriptor
usb_get_descriptor
usb_control_msg
usb_internal_control_msg
usb_start_wait_urb
usb_submit_urb / wait_for_completion_timeout / usb_kill_urb

hub_port_init
hub_set_address
xhci_address_device
xhci_setup_device

Mathias Nyman explains the current behaviour violates the XHCI spec:

hub_port_reset() will end up moving the corresponding xhci device slot to default state.

As hub_port_reset() is called several times in hub_port_init() it sounds reasonable that we could end up with two threads having their xhci device slots in default state at the same time, which according to xhci 4.5.3 specs still is a big no no:

"Note: Software shall not transition more than one Device Slot to the
Default State at a time"

So both threads fail at their next task after this.
One fails to read the descriptor, and the other fails addressing the device.

Fix this in hub_port_init by locking the USB controller (instead of an individual bus) to prevent simultaneous initialisation of both buses.

---
 drivers/usb/core/hcd.c  |   15 +++++++++++++--
 drivers/usb/core/hub.c  |    8 ++++----
 include/linux/usb.h     |    3 +--
 include/linux/usb/hcd.h |    1 +
 4 files changed, 19 insertions(+), 8 deletions(-)

@@ -966,7 +966,7 @@ static void usb_bus_init (struct usb_bus
 	bus->bandwidth_allocated = 0;
 	bus->bandwidth_int_reqs  = 0;
 	bus->bandwidth_isoc_reqs = 0;
-	mutex_init(&bus->usb_address0_mutex);
+	mutex_init(&bus->devnum_next_mutex);
 
 	INIT_LIST_HEAD (&bus->bus_list);
 }

@@ -2497,6 +2497,14 @@ struct usb_hcd *usb_create_shared_hcd(co
 		return NULL;
 	}
 	if (primary_hcd == NULL) {
+		hcd->address0_mutex = kmalloc(sizeof(*hcd->address0_mutex),
+				GFP_KERNEL);
+		if (!hcd->address0_mutex) {
+			kfree(hcd);
+			dev_dbg(dev, "hcd address0 mutex alloc failed\n");
+			return NULL;
+		}
+		mutex_init(hcd->address0_mutex);
 		hcd->bandwidth_mutex = kmalloc(sizeof(*hcd->bandwidth_mutex),
 				GFP_KERNEL);
 		if (!hcd->bandwidth_mutex) {

@@ -2508,6 +2516,7 @@ struct usb_hcd *usb_create_shared_hcd(co
 		dev_set_drvdata(dev, hcd);
 	} else {
 		mutex_lock(&usb_port_peer_mutex);
+		hcd->address0_mutex = primary_hcd->address0_mutex;
 		hcd->bandwidth_mutex = primary_hcd->bandwidth_mutex;
 		hcd->primary_hcd = primary_hcd;
 		primary_hcd->primary_hcd = primary_hcd;

@@ -2574,8 +2583,10 @@ static void hcd_release(struct kref *kre
 	struct usb_hcd *hcd = container_of (kref, struct usb_hcd, kref);
 
 	mutex_lock(&usb_port_peer_mutex);
-	if (usb_hcd_is_primary_hcd(hcd))
+	if (usb_hcd_is_primary_hcd(hcd)) {
+		kfree(hcd->address0_mutex);
 		kfree(hcd->bandwidth_mutex);
+	}
 	if (hcd->shared_hcd) {
 		struct usb_hcd *peer = hcd->shared_hcd;
 

@@ -1980,7 +1980,7 @@ static void choose_devnum(struct usb_dev
 	struct usb_bus	*bus = udev->bus;
 
 	/* be safe when more hub events are proceed in parallel */
-	mutex_lock(&bus->usb_address0_mutex);
+	mutex_lock(&bus->devnum_next_mutex);
 	if (udev->wusb) {
 		devnum = udev->portnum + 1;
 		BUG_ON(test_bit(devnum, bus->devmap.devicemap));

@@ -1998,7 +1998,7 @@ static void choose_devnum(struct usb_dev
 		set_bit(devnum, bus->devmap.devicemap);
 		udev->devnum = devnum;
 	}
-	mutex_unlock(&bus->usb_address0_mutex);
+	mutex_unlock(&bus->devnum_next_mutex);
 }
 
 static void release_devnum(struct usb_device *udev)

@@ -4262,7 +4262,7 @@ hub_port_init(struct usb_hub *hub, struc
 	if (oldspeed == USB_SPEED_LOW)
 		delay = HUB_LONG_RESET_TIME;
 
-	mutex_lock(&hdev->bus->usb_address0_mutex);
+	mutex_lock(hcd->address0_mutex);
 
 	/* Reset the device; full speed may morph to high speed */
 	/* FIXME a USB 2.0 device may morph into SuperSpeed on reset. */

@@ -4548,7 +4548,7 @@ fail:
 		hub_port_disable(hub, port1, 0);
 		update_devnum(udev, devnum);	/* for disconnect processing */
 	}
-	mutex_unlock(&hdev->bus->usb_address0_mutex);
+	mutex_unlock(hcd->address0_mutex);
 	return retval;
 }
 

@@ -371,14 +371,13 @@ struct usb_bus {
 
 	int devnum_next;		/* Next open device number in
 					 * round-robin allocation */
+	struct mutex devnum_next_mutex; /* devnum_next mutex */
 
 	struct usb_devmap devmap;	/* device address allocation map */
 	struct usb_device *root_hub;	/* Root hub */
 	struct usb_bus *hs_companion;	/* Companion EHCI bus, if any */
 	struct list_head bus_list;	/* list of busses */
 
-	struct mutex usb_address0_mutex; /* unaddressed device mutex */
-
 	int bandwidth_allocated;	/* on this bus: how much of the time
 					 * reserved for periodic (intr/iso)
 					 * requests is used, on average?

@@ -180,6 +180,7 @@ struct usb_hcd {
 	 * bandwidth_mutex should be dropped after a successful control message
 	 * to the device, or resetting the bandwidth after a failed attempt.
 	 */
+	struct mutex		*address0_mutex;
 	struct mutex		*bandwidth_mutex;
 	struct usb_hcd		*shared_hcd;
 	struct usb_hcd		*primary_hcd;

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/usb-core-hub-hub_port_init-lock-controller-instead-of-bus.patch