On Mon, 10 Sep 2012, Don Zickus wrote:
> A customer of ours noticed that after a bunch of hot removals of the EHCI
> PCI device, a panic occurs. This happened on a 2.6.32 RHEL-6 kernel, but
> I believe is still applicable upstream.
>
> The panic was further simplified to enabling SLUB debug poisoning and running
> the following command:
>
> while true; do find /proc/bus/usb -type f -exec cat {} >/dev/null \; ; done &
>
> This gets the machine to panic after 1 or 2 removals of the device.
> This is likely because the following thread was in the process of removing the
> device:
> The fix that solved their problem was to deregister the usb bus first before
> running usb_put_dev. After running multiple tests the panic disappeared.
>
> Deregistering the bus first to prevent future readers from accessing the
> device
> before cleaning up the hcd, seemed like an appropriate way to go. I'll leave
> it to the experts to validate that or provide a better solution. :-)
>
> I adapted their usb_remove_hcd fix for usb_add_hcd error path too to mimic
> the same behaviour (a little code shuffling to handle the gotos cleanly).
Moving things around in usb_add_hcd() is not a good way to attack this
problem. Here's a better approach; please make sure that it does what
you want. The idea is to indicate that a root hub is not registered by
setting its devnum field to 0.
Alan Stern
Index: usb-3.6/drivers/usb/core/devices.c
===================================================================
--- usb-3.6.orig/drivers/usb/core/devices.c
+++ usb-3.6/drivers/usb/core/devices.c
@@ -624,7 +624,7 @@ static ssize_t usb_device_read(struct fi
/* print devices for all busses */
list_for_each_entry(bus, &usb_bus_list, bus_list) {
/* recurse through all children of the root hub */
- if (!bus->root_hub)
+ if (!bus->root_hub || bus->root_hub->devnum == 0)
continue;
usb_lock_device(bus->root_hub);
ret = usb_device_dump(&buf, &nbytes, &skip_bytes, ppos,
Index: usb-3.6/drivers/usb/core/hcd.c
===================================================================
--- usb-3.6.orig/drivers/usb/core/hcd.c
+++ usb-3.6/drivers/usb/core/hcd.c
@@ -980,6 +980,8 @@ static int register_root_hub(struct usb_
const int devnum = 1;
int retval;
+ mutex_lock(&usb_bus_list_lock);
+
usb_dev->devnum = devnum;
usb_dev->bus->devnum_next = devnum + 1;
memset (&usb_dev->bus->devmap.devicemap, 0,
@@ -987,8 +989,6 @@ static int register_root_hub(struct usb_
set_bit (devnum, usb_dev->bus->devmap.devicemap);
usb_set_device_state(usb_dev, USB_STATE_ADDRESS);
- mutex_lock(&usb_bus_list_lock);
-
usb_dev->ep0.desc.wMaxPacketSize = cpu_to_le16(64);
retval = usb_get_device_descriptor(usb_dev, USB_DT_DEVICE_SIZE);
if (retval != sizeof usb_dev->descriptor) {
@@ -1011,6 +1011,7 @@ static int register_root_hub(struct usb_
if (retval) {
dev_err (parent_dev, "can't register root hub for %s, %d\n",
dev_name(&usb_dev->dev), retval);
+ usb_dev->devnum = 0;
}
mutex_unlock(&usb_bus_list_lock);
@@ -2527,6 +2528,7 @@ error_create_attr_group:
#endif
mutex_lock(&usb_bus_list_lock);
usb_disconnect(&rhdev); /* Sets rhdev to NULL */
+ hcd->self.root_hub->devnum = 0;
mutex_unlock(&usb_bus_list_lock);
err_register_root_hub:
hcd->rh_pollable = 0;
@@ -2583,6 +2585,7 @@ void usb_remove_hcd(struct usb_hcd *hcd)
mutex_lock(&usb_bus_list_lock);
usb_disconnect(&rhdev); /* Sets rhdev to NULL */
+ hcd->self.root_hub->devnum = 0;
mutex_unlock(&usb_bus_list_lock);
/* Prevent any more root-hub status calls from the timer.
--
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