Message-ID: <20180102025417.GA20740@js1304-P5Q-DELUXE>
Date:   Tue, 2 Jan 2018 11:54:18 +0900
From:   Joonsoo Kim <iamjoonsoo.kim@....com>
To:     Jonathan McDowell <noodles@...th.li>
Cc:     linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, netdev@...r.kernel.org
Subject: Re: ACPI issues on cold power on [bisected]

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.

Although slab change revealed this problem, I think that problem is on
ACPI side and need to be fixed there.

Anyway, I'm not sure why it doesn't happen before. These ACPI
initialization code looks not changed for a long time. Could you test
this problem with the slub?

Thanks.

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