linux-kernel - Re: WARNING: at drivers/usb/host/ehci-hcd.c:287

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Message-ID: <Pine.LNX.4.44L0.0803041553320.15986-100000@iolanthe.rowland.org>
Date:	Tue, 4 Mar 2008 15:57:51 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	David Brownell <david-b@...bell.net>
cc:	Christian Kujau <lists@...dbynature.de>,
	LKML <linux-kernel@...r.kernel.org>, <0x0007@...il.com>,
	USB list <linux-usb@...r.kernel.org>
Subject: Re: WARNING: at drivers/usb/host/ehci-hcd.c:287

On Tue, 4 Mar 2008, David Brownell wrote:

> On Tuesday 04 March 2008, Alan Stern wrote:
> > Dave, it seems to me that this must be an example of a race between the 
> > iaa watchdog timer expiring and end_unlink_async() running.  It's not 
> > good enough for end_unlink_async() to call iaa_watchdog_done(), because 
> > on an SMP system the timer may already have fired and the watchdog 
> > routine may be spinning on ehci->lock.
> 
> Right.
> 
> 
> > How about replacing the
> > 
> >         WARN_ON(!ehci->reclaim);
> 
> Or bettter yet, just removing it entirely.  ISTR doing that in some
> patches I've not yet sent for merging, and expect that's what my
> preferred fix will be ...

But removing the WARN_ON won't fix the problem.  The routine still
needs to exit immediately if ehci->reclaim isn't set, the root hub
isn't running, or the timer has been restarted.

Alan Stern

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