On Sat, Oct 20, 2018 at 11:12:16PM +0200, Hans Verkuil wrote:
> Hi Sean,
>
> Can you take a look at this, it appears to be an RC issue, see my analysis
> below.
>
> On 10/20/2018 03:26 PM, Torbjorn Jansson wrote:
> > Hello
> >
> > i'm using the pulse8 usb cec adapter to control my tv.
> > i have a few scripts that poll the power status of my tv and after a while
> > it stops working returning errors when trying to check if tv is on or off.
> > this i think matches a kernel oops i'm seeing that i suspect is related to
> > this.
> >
> > i have sometimes been able to recover from this problem by completely
> > cutting power to my tv and also unplugging the usb cec adapter.
> > i have a feeling that the tv is at least partly to blame for cec-ctl not
> > working but in any case there shouldn't be a kernel oops.
> >
> >
> > also every now and then i see this in dmesg:
> > cec cec0: transmit: failed 05
> > cec cec0: transmit: failed 06
> > but that doesn't appear to do any harm as far as i can tell.
> >
> > any idea whats causing the oops?
> >
> > the ops:
> >
> > BUG: unable to handle kernel NULL pointer dereference at 0000000000000038
> > PGD 0 P4D 0
> > Oops: 0000 [#1] SMP PTI
> > CPU: 9 PID: 27687 Comm: kworker/9:2 Tainted: P OE
> > 4.18.12-200.fc28.x86_64 #1
> > Hardware name: Supermicro C7X99-OCE-F/C7X99-OCE-F, BIOS 2.1a 06/15/2018
> > Workqueue: events pulse8_irq_work_handler [pulse8_cec]
> > RIP: 0010:ir_lirc_scancode_event+0x3d/0xb0 [rc_core]
>
> Huh. ir_lirc_scancode_event() calls spin_lock_irqsave(&dev->lirc_fh_lock,
> flags);
>
> The spinlock dev->lirc_fh_lock is initialized in ir_lirc_register(), which is
> called
> from rc_register_device(), except when the protocol is CEC:
>
> /* Ensure that the lirc kfifo is setup before we start the thread */
> if (dev->allowed_protocols != RC_PROTO_BIT_CEC) {
> rc = ir_lirc_register(dev);
> if (rc < 0)
> goto out_rx;
> }
>
> So it looks like ir_lirc_scancode_event() fails because dev->lirc_fh_lock was
> never
> initialized.
>
> Could this be fall-out from the lirc changes you did not too long ago?
Yes, this is broken. My bad, sorry. I think this must have been broken since
v4.16. I can write a patch but I don't have a patch but I'm on the train
to ELCE in Edinburgh now, with no hardware to test on.
Sean
