linux-kernel - [BUG] usb/core/hub.c loops forever on resume from ram due to bluetooth

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Message-ID: <4637CD25.5070104@rtr.ca>
Date:	Tue, 01 May 2007 19:28:37 -0400
From:	Mark Lord <lkml@....ca>
To:	Linux Kernel <linux-kernel@...r.kernel.org>, marcel@...tmann.org,
	Greg KH <gregkh@...e.de>, Andrew Morton <akpm@...l.org>
Subject: [BUG] usb/core/hub.c loops forever on resume from ram due to bluetooth

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@...ox.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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