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SubjectRe: WARNING: at drivers/usb/host/ehci-hcd.c:287
On Mon, 3 Mar 2008, Christian Kujau wrote:

> On Mon, 3 Mar 2008, Christian Kujau wrote:
> > after upgrading to 2.6.25-rc3, kern.log shows:
> >
> > [ 1535.884848] ------------[ cut here ]------------
> > [ 1535.884855] WARNING: at drivers/usb/host/ehci-hcd.c:287
>
> Hm, after ~24h of uptime, this message appeared 25 times already.
> The WLAN USB device was used the whole time, the usb-storage module
> was hardly used over the day:
>
> # grep usb /proc/interrupts
> 10: 10693403 XT-PIC-XT ohci_hcd:usb3, eth0
> 11: 10270770 XT-PIC-XT sym53c8xx, ehci_hcd:usb1
> 12: 91 XT-PIC-XT ohci_hcd:usb2
>
> I even tried to trigger the system freeze[0] by using usb-storage
> and reading a lot from it, but no freeze, and the message could
> not be triggered either - they pop up every now and then, but too often,
> IMHO.
>
> Can anybody shed some light on this?

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.

It's even worse, because end_unlink_async() can call
start_unlink_async(). If that happens, the watchdog routine will think
the timer has expired when in fact it has just been restarted.

How about replacing the

WARN_ON(!ehci->reclaim);

line in ehci_iaa_watchdog() with

if (unlikely(!ehci->reclaim ||
!HC_IS_RUNNING(ehci_to_hcd(ehci)->state) ||
timer_pending(&ehci->iaa_watchdog))
goto done;
where "done:" is added just before the spin_unlock_irqrestore?

Alan Stern



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