Date: Sat, 5 Feb 2011 22:19:26 -0500 (EST)
From: Alan Stern <stern@rowland.harvard.edu>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
cc: Minchan Kim <minchan.kim@gmail.com>,
        linux kernel mailing list <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@suse.de>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [BUG] usb_set_device_state
In-Reply-To: <201102060006.45175.rjw@sisk.pl>
Message-ID: <Pine.LNX.4.44L0.1102052211040.9798-100000@netrider.rowland.org>
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On Sun, 6 Feb 2011, Rafael J. Wysocki wrote:

> On Saturday, February 05, 2011, Alan Stern wrote:
> > On Sun, 6 Feb 2011, Minchan Kim wrote:
> > 
> > > I got following message during booting mmotm-02-04.
...
> > > It seems usb_set_device_state disable irq by spin_lock_irqsave.
> > > But it calls device_set_wakeup_capable which ends up calling sysfs_merge_group.
> > > It calls mutex_lock. :(
> > > 
> > > Is it already known BUG?
> > 
> > No, it was newly introduced by changes to the 
> > device_set_wakeup_capable() routine.  Rafael, this sort of problem may 
> > occur in other places too, since previously there was no requirement 
> > that device_set_wakeup_capable() be called in process context.
> 
> I'm aware of that, but it's only happend in a handful of network drivers so far.
> 
> I think this is a new case in -mm, though, isn't it?

I'm not sure.  The USB core does call device_set_wakeup_capable()  
while holding one or more spinlocks in usb_set_device_state(), and that
routine is called in several places.  You ought to be able to duplicate 
the error on your own system simply by plugging in a USB hub.

Alan Stern

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