On Tue, Jan 2, 2018 at 3:54 AM, Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> 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()? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
