linux-kernel - Re: [PATCH] USB: fix deadlock in HCD code

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Message-ID: <Pine.LNX.4.44L0.0805211042070.2490-100000@iolanthe.rowland.org>
Date:	Wed, 21 May 2008 10:46:45 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Jiri Kosina <jkosina@...e.cz>
cc:	Oliver Neukum <oliver@...kum.org>, Greg KH <greg@...ah.com>,
	<linux-usb@...r.kernel.org>, <lchiquitto@...ell.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] USB: fix deadlock in HCD code

On Wed, 21 May 2008, Jiri Kosina wrote:

> On Wed, 21 May 2008, Alan Stern wrote:
> 
> > > Used in the suspend code. Your patch is indeed correct, but I fear 
> > > there might be a second bug caused by wrong calling conditions.
> > The problem in the Novell bugzilla entry was caused by the fact that the 
> > OHCI irq routine was invoked with interrupts enabled, owing to a missing 
> > IRQF_DISABLED flag.  That bug has already been fixed in 2.6.25.
> 
> That indeed is 2.6.25 kernel. I guess you are talking about commit 
> 442258e2ff69 here.

Yes.

> If so, the reporter is definitely using the kernel 
> containing this commit, and the lockups still trigger.
> 
> Seems that my patch is papering over the real bug (someone enabling 
> interrupts somewhere) indeed, but I can't seem to be able to find such 
> codepath.

You could try testing the interrupt-enable flag at various places 
in ohci-hcd (start with finish_urb) and printing an error message if 
interrupts are enabled.

One possibility is that in an earlier call to finish_urb,
usb_hcd_giveback_urb was called with interrupts disabled and returned 
with interrupts enabled.  In other words, some driver's callback 
routine may have enabled interrupts incorrectly.

Alan Stern

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