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.
Fixes: 638139eb95d2 ("usb: hub: allow to process more usb hub events in parallel")
Link: https://lkml.org/lkml/2016/2/8/312
Link: https://lkml.org/lkml/2016/2/4/748
Signed-off-by: Chris Bainbridge <chris.bainbridge@xxxxxxxxx>
---
This is technically the same as the last patch version, but with a reworked
commit message to better explain the cause of the issue.
---
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(-)
diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index 2ca2cef7f681..980fc5774151 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -994,7 +994,7 @@ static void usb_bus_init (struct usb_bus *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);
}
/*-------------------------------------------------------------------------*/
@@ -2521,6 +2521,14 @@ struct usb_hcd *usb_create_shared_hcd(const struct hc_driver *driver,
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) {
@@ -2532,6 +2540,7 @@ struct usb_hcd *usb_create_shared_hcd(const struct hc_driver *driver,
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;
@@ -2598,8 +2607,10 @@ static void hcd_release(struct kref *kref)
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;
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 38cc4bae0a82..1ab42bfbecaf 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -2080,7 +2080,7 @@ static void choose_devnum(struct usb_device *udev)
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));
@@ -2098,7 +2098,7 @@ static void choose_devnum(struct usb_device *udev)
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)
@@ -4364,7 +4364,7 @@ hub_port_init(struct usb_hub *hub, struct usb_device *udev, int port1,
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. */
@@ -4650,7 +4650,7 @@ 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;
}
diff --git a/include/linux/usb.h b/include/linux/usb.h
index 6a9a0c28415d..0f6b7c734d2d 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -374,13 +374,12 @@ 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 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?
diff --git a/include/linux/usb/hcd.h b/include/linux/usb/hcd.h
index b98f831dcda3..66fc13705ab7 100644
--- a/include/linux/usb/hcd.h
+++ b/include/linux/usb/hcd.h
@@ -181,6 +181,7 @@ 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;
--
2.1.4
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