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Subject[PATCH] usb: host: xhci: Replace bus lock with host controller lock
Date
The XHCI controller presents two USB buses to the system - one for USB 2
and one for USB 3. When only one bus is locked there is a race condition
during hub init that results in errors like:

[ 13.183701] usb 3-3: device descriptor read/all, error -110

On a test system this error occurred on 6% of boots. Fix this by locking
the bus controller instead of the bus, thus preventing simultaneous hub
init on both buses.

Fixes: 638139eb95d2 ("usb: hub: allow to process more usb hub events in parallel")
Signed-off-by: Chris Bainbridge <chris.bainbridge@gmail.com>
---
drivers/usb/core/hcd.c | 2 +-
drivers/usb/core/hub.c | 8 ++++----
include/linux/usb.h | 3 +--
3 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index df0e3b92533a..c468d047ec5e 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -966,7 +966,7 @@ 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);

INIT_LIST_HEAD (&bus->bus_list);
}
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 350dcd9af5d8..e03c2f05c2f6 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -2066,7 +2066,7 @@ 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));
@@ -2084,7 +2084,7 @@ 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)
@@ -4312,7 +4312,7 @@ 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(&hdev->bus->controller->mutex);

/* Reset the device; full speed may morph to high speed */
/* FIXME a USB 2.0 device may morph into SuperSpeed on reset. */
@@ -4588,7 +4588,7 @@ fail:
hub_port_disable(hub, port1, 0);
update_devnum(udev, devnum); /* for disconnect processing */
}
- mutex_unlock(&hdev->bus->usb_address0_mutex);
+ mutex_unlock(&hdev->bus->controller->mutex);
return retval;
}

diff --git a/include/linux/usb.h b/include/linux/usb.h
index 89533ba38691..6b736c82b9d1 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -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?
--
2.1.4
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