Re: [PATCH] USB: fix deadlock in HCD code

From: Alan Stern
Date: Wed May 21 2008 - 10:46:56 EST

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.


> 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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