Re: [BUG] usb/core/hub.c loops forever on resume from ram due to bluetooth

Mark Lord
2007-05-08T13:53:10Z

Greg ?

The oddball thing here is that on a UP machine with a UP kernel,
this (below) was never an issue.

After moving the drive to a dual-core machine and rebuilding
the kernel with SMP=y, the problem becomes a killer here.
The two machines are nearly identical, apart from the CPUs.

The failing machine is a Dell Inspiron 9400,
and mine isn't the only unit that has this issue.

----------Original message:

I have just replaced my primary single-core notebook
with a nearly identical dual-core notebook,
and moved the usb-bluetooth peripheral from the old
machine to the new one.

On the single-core machine, suspend/resume (RAM) worked
fine even with the bluetooth module enabled.

On the new dual-core machine, resuming with bluetooth
enabled results in an infinite(?) lockup in an unbounded
loop in hub_tt_kevent(). With PM debug on, I see
tens of thousands of these messages scrolling on the console:

kernel: usb 5-1: clear tt 4 (9042) error -71
kernel: usb 5-1: clear tt 4 (9042) error -71
kernel: usb 5-1: clear tt 4 (9042) error -71
(over and over and ...)

By restricting iterations on the unbounded loop
the machine is able to resume again.

Greg / Marcel: any words of wisdom?

And we should probably put bounds permanently on that loop:

I devised/used this patch to accomplish it.
Now, I still get close to a thousand or so such
messages, in groups, showing up in syslog,
but at least the system can resume after suspend.

Signed-off-by: Mark Lord <mlord@pobox.com>

--- linux/drivers/usb/core/hub.c.orig 2007-04-26 12:02:47.000000000 -0400
+++ linux/drivers/usb/core/hub.c 2007-05-01 18:48:46.000000000 -0400
@@ -403,9 +403,10 @@
struct usb_hub *hub =
container_of(work, struct usb_hub, tt.kevent);
unsigned long flags;
+ int limit = 500;

spin_lock_irqsave (&hub->tt.lock, flags);
- while (!list_empty (&hub->tt.clear_list)) {
+ while (--limit && !list_empty (&hub->tt.clear_list)) {
struct list_head *temp;
struct usb_tt_clear *clear;
struct usb_device *hdev = hub->hdev;
-----

-
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