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

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Date:	Wed, 2 May 2007 15:59:26 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Mark Lord <lkml@....ca>
cc:	Linux Kernel <linux-kernel@...r.kernel.org>, <marcel@...tmann.org>,
	Greg KH <gregkh@...e.de>, Andrew Morton <akpm@...l.org>,
	<linux-usb-devel@...ts.sourceforge.net>
Subject: Re: [linux-usb-devel] [BUG] usb/core/hub.c loops forever on resume
 from ram due to bluetooth

On Tue, 1 May 2007, Mark Lord wrote:

> 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.

A better approach would be to find out why your system gets into that loop 
and fix the underlying cause.

Alan Stern

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