Messages in this thread | | | Date | Thu, 24 Mar 2011 08:27:55 -0400 | From | Konrad Rzeszutek Wilk <> | Subject | Re: [Xen-devel] Re: 2.6.39 crashes BUG: unable to handle kernel NULL pointer dereference at 000000000000042 .. cmos_checkintr+0x4d/0x55 under Xen as PV guest. |
| |
On Tue, Mar 22, 2011 at 10:38:41AM -0400, Konrad Rzeszutek Wilk wrote: > > > No. 2.6.38 vaniall works great. > > > > Ok. Hrm. > > > > > > Any insight there? > > > > > > I hoped you might have :-) > > > > Could you help me understand where in the probe logic xen bombs out of > > the cmos code? > > Sure. The issue is that rtc_update_irq calls schedule_work with rtc->irqwork > which has not been initialized. The reason for that is that rtc_device_register > has never been called.. uh wait, that does not make sense, it is called in > cmos_do_probe. Hmm, let get find out exactly on which variable queue_work_on > bombs out on.
The problem is this:
cmos_do_probe does:
cmos_rtc.dev = dev; dev_set_drvdata(dev, &cmos_rtc);
which means that dev->p->private_data contains cmos_rtc. And dev->p->private_data->rtc is a NULL pointer. The next function:
cmos_rtc.rtc = rtc_device_register(driver_name, dev, &cmos_rtc_ops, THIS_MODULE);
'rtc_device_register' creates an 'rtc' structure and sets its parent to be: rtc->dev.parent = dev;
and later on it does: if (!err && !rtc_valid_tm(&alrm.time)) rtc_set_alarmtrtc, &alrm);
rtc_set_alarm calls rtc_timer_enqueue which calls __rtc_set_alarm. __rtc_set_alarms calls 'cmos_set_alarm' via: err = rtc->ops->set_alarm(rtc->dev.parent, alarm);
which is basically passing in 'dev' to 'cmos_set_alarm', and 'cmos_set_alarm' uses the dev to: struct cmos_rtc *cmos = dev_get_drvdata(dev);
(so get the from dev->p->private_data the cmos_rtc). get the 'cmos' (which is what 'cmos_rtc'). Great... except then it ends up trying to dereference cmos->rtc.irqwork (via cmos_irq_disable(cmos, .. and somehere in its chain calls schedule_work(cmos->rtc) whcih ends up blowing up b/c cmos_rtc.rtc has not been set yet.
The cmos_rtc.rtc is set when the when 'rtc_device_register' finish, which it hadn't yet done.
git gui blame tells me to look at f44f7f96a20af16f6f12e1c995576d6becf5f57b
| |