Re: 2.6.26-00000-g8be1a6d - WARNING: at drivers/base/power/main.c:82

From: Alan Stern
Date: Wed Jul 30 2008 - 10:24:49 EST


On Wed, 30 Jul 2008, Andrew Morton wrote:

> On Mon, 28 Jul 2008 13:33:21 +0200 Roberto Oppedisano <roppedisano@xxxxxxxxxxxxxx> wrote:
>
> > More info on request.
> >
>
> Let's cc linux-usb, as that appears to be the subsystem which triggered
> this:
>
> int device_pm_add(struct device *dev)
> {
> int error;
>
> pr_debug("PM: Adding info for %s:%s\n",
> dev->bus ? dev->bus->name : "No Bus",
> kobject_name(&dev->kobj));
> mutex_lock(&dpm_list_mtx);
> if (dev->parent) {
> if (dev->parent->power.status >= DPM_SUSPENDING) {
> dev_warn(dev, "parent %s is sleeping, will not add\n",
> dev->parent->bus_id);
> WARN_ON(true);
> }
>
> WARN_ON.
>
> Also, I assume that your kernel did print that "parent %s is sleeping"
> message, but you trimmed it off. That would probably be useful
> information.

Hmmm... I don't suppose anyone ever thought to indicate which kernel
version produced this warning?

If you look at the offending source code in 2.6.27-rc1, you'll find a
comment that explains the whole thing. From do_unbind_rebind() --
admittedly not easy to single out from the rather lengthy stack trace
-- in drivers/usb/core/driver.c:

/* FIXME: The next line is needed because we are going to probe
* the interface, but as far as the PM core is concerned the
* interface is still suspended. The problem wouldn't exist
* if we could rebind the interface during the interface's own
* resume() call, but at the time the usb_device isn't locked!
*
* The real solution will be to carry this out during the device's
* complete() callback. Until that is implemented, we have to
* use this hack.
*/
// intf->dev.power.sleeping = 0;

The last line had to be commented out because the power.sleeping field
was removed during the transition from 2.6.26 to 2.6.27-rc1. The code
that will make this work properly, with no warnings, hasn't been
written yet; I was waiting for 2.6.27-rc1 to appear so there'd be a
more-or-less stable base to work from.

For the time being you can simply ignore the WARNING; it is harmless.

Alan Stern

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