Re: ACPI issues on cold power on [bisected]

[Joonsoo Kim <iamjoonsoo.kim@lge.com>]

On Tue, Jan 02, 2018 at 11:25:01AM +0100, Rafael J. Wysocki wrote:
> On Tue, Jan 2, 2018 at 3:54 AM, Joonsoo Kim <iamjoonsoo.kim@lge.com> wrote:
> > On Fri, Dec 29, 2017 at 04:36:59PM +0000, Jonathan McDowell wrote:
> >> On Fri, Dec 22, 2017 at 09:21:09AM +0900, Joonsoo Kim wrote:
> >> > On Fri, Dec 08, 2017 at 03:11:59PM +0000, Jonathan McDowell wrote:
> >> > > I've been sitting on this for a while and should have spent time to
> >> > > investigate sooner, but it's been an odd failure mode that wasn't quite
> >> > > obvious.
> >> > >
> >> > > In 4.9 if I cold power on my laptop (Dell E7240) it fails to boot - I
> >> > > don't see anything after grub says its booting. In 4.10 onwards the
> >> > > laptop boots, but I get an Oops as part of the boot and ACPI is unhappy
> >> > > (no suspend, no clean poweroff, no ACPI buttons). The Oops is below;
> >> > > taken from 4.12 as that's the most recent error dmesg I have saved but
> >> > > also seen back in 4.10. It's always address 0x30 for the dereference.
> >> > >
> >> > > Rebooting the laptop does not lead to these problems; it's *only* from a
> >> > > complete cold boot that they arise (which didn't help me in terms of
> >> > > being able to reliably bisect). Once I realised that I was able to
> >> > > bisect, but it leads me to an odd commit:
> >> > >
> >> > > 86d9f48534e800e4d62cdc1b5aaf539f4c1d47d6
> >> > > (mm/slab: fix kmemcg cache creation delayed issue)
> >> > >
> >> > > If I revert this then I can cold boot without problems.
> >> > >
> >> > > Also I don't see the problem with a stock Debian kernel, I think because
> >> > > the ACPI support is modularised.
> >> >
> >> > Sorry for late response. I was on a long vacation.
> >>
> >> No problem. I've been trying to get around to diagnosing this for a
> >> while now anyway and this isn't a great time of year for fast responses.
> >>
> >> > I have tried to solve the problem however I don't find any clue yet.
> >> >
> >> > >From my analysis, oops report shows that 'struct sock *ssk' passed to
> >> > netlink_broadcast_filtered() is NULL. It means that some of
> >> > netlink_kernel_create() returns NULL. Maybe, it is due to slab
> >> > allocation failure. Could you check it by inserting some log on that
> >> > part? The issue cannot be reproducible in my side so I need your help.
> >>
> >> I've added some debug in acpi_bus_generate_netlink_event +
> >> genlmsg_multicast and the problem seems to be that genlmsg_multicast is
> >> getting called when init_net.genl_sock has not yet been initialised,
> >> leading to the NULL deference.
> >>
> >> Full dmesg output from a cold 4.14.8 boot at:
> >>
> >> https://the.earth.li/~noodles/acpi-problem/dmesg-4.14.8-broken
> >>
> >> And the same kernel after a reboot ("shutdown -r now"):
> >>
> >> https://the.earth.li/~noodles/acpi-problem/dmesg-4.14.8-working
> >>
> >> Patch that I've applied is at
> >>
> >> https://the.earth.li/~noodles/acpi-problem/debug-acpi.diff
> >>
> >
> > Thanks for testing! It's very helpful.
> >
> >> The interesting difference seems to be:
> >>
> >>  PCI: Using ACPI for IRQ routing
> >> +ACPI: Generating event type 208 (:9DBB5994-A997-11DA-B012-B622A1EF5492)
> >> +ERROR: init_net.genl_sock is NULL
> >> +BUG: unable to handle kernel NULL pointer dereference at 0000000000000030
> >> +IP: netlink_broadcast_filtered+0x20/0x3d0
> >> +PGD 0 P4D 0
> >> +Oops: 0000 [#1] SMP
> >> +Modules linked in:
> >> +CPU: 0 PID: 29 Comm: kworker/0:1 Not tainted 4.14.8+ #1
> >> +Hardware name: Dell Inc. Latitude E7240/07RPNV, BIOS A22 10/18/2017
> >> +Workqueue: kacpi_notify acpi_os_execute_deferred
> >>
> >> 9DBB5994-A997-11DA-B012-B622A1EF5492 is the Dell WMI event GUID and
> >> there's no visible event for it on a reboot, just on a cold power on.
> >> Some sort of ordering issues such that genl_sock is being initialised
> >> later with the slab change?
> >
> > I have checked that there is an ordering issue.
> >
> > genl_init() which initializes init_net->genl_sock is called on
> > subsys_initcall().
> >
> > acpi_wmi_init() which schedules acpi_wmi_notify_handler() to the
> > workqueue is called on subsys_initcall(), too.
> > (acpi_wmi_notify_handler() -> acpi_bus_generate_netlink_event() ->
> > netlink_broadcast())
> >
> > In my system, acpi_wmi_init() is called before the genl_init().
> > Therefore, if the worker is scheduled before genl_init() is done, NULL
> > derefence would happen.
> 
> Does it help to change the subsys_initcall() in wmi.c to subsys_initcall_sync()?

I guess that it would work. I cannot reproduce the issue so it needs
to be checked by Jonathan. Jonathan, could you check the problem
is disappeared with above change?

Thanks.

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