linux-kernel - Re: deadlock in "modprobe -r ohci1394" shortly after "modprobe ohci1394"

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Message-ID: <Pine.LNX.4.44L0.0611201626390.7916-100000@iolanthe.rowland.org>
Date:	Mon, 20 Nov 2006 16:28:32 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Stefan Richter <stefanr@...6.in-berlin.de>
cc:	linux1394-devel@...ts.sourceforge.net,
	Greg Kroah-Hartman <gregkh@...e.de>,
	<linux-kernel@...r.kernel.org>
Subject: Re: deadlock in "modprobe -r ohci1394" shortly after "modprobe
 ohci1394"

On Mon, 20 Nov 2006, Stefan Richter wrote:

> Alan Stern wrote:
> > Wait a minute.  Above you agreed that the problem was caused by knodemgrd 
> > attempting to rescan the host's _parent_.  So which is the focus of the 
> > deadlock: the host or its parent?
> 
> The parent of the hpsb_host.
> 
> ohci1394 works on a pci_dev which contains a dev, let's call it A.
> 
> ieee1394 has a hpsb_host which contains a dev, let's call it B. B's
> parent is A. Then there is one or more node_entry with dev C whose
> parent is B, end unit_directory with dev D whose parent is C.
> 
> The bus of devices B, C, D is set to be ieee1394_bus_type, and that's
> what knodemgrd is scanning.
> 
> knodemgrd blocks on the semaphore of the parent of B because
> driver_detach took the semaphore of A (and of the parent of A if there
> is one).

Okay, I get it.

> > Is the problem caused by the fact that some of these struct device's 
> > aren't bound to a driver?  Remember, bus_rescan_devices() will skip over 
> > anything that already has a driver.  Could you solve your problem by 
> > adding a do_nothing driver that would bind to these otherwise unused 
> > devices?
> 
> Excellently, that's what I will try in a minute. It is surely intended
> that the hpsb_host can get a driver bound too, but as I mentioned, we
> don't have a driver which needs this capability and I don't foresee any
> such driver.
> 
> Thanks for the directions.

You're welcome.  Let me know how it turns out.

Alan Stern

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