Hi, On 1/27/22 14:33, Rafael J. Wysocki wrote: > On Thu, Jan 27, 2022 at 2:05 PM Hans de Goede <hdegoede@xxxxxxxxxx> wrote: >> >> Hi, >> >> On 1/26/22 18:11, Rafael J. Wysocki wrote: >>> On Wed, Jan 26, 2022 at 5:41 PM Hans de Goede <hdegoede@xxxxxxxxxx> wrote: >>>> >>>> Hi, >>>> >>>> On 1/26/22 16:54, Rafael J. Wysocki wrote: >>>>> On Wed, Jan 26, 2022 at 2:47 PM Hans de Goede <hdegoede@xxxxxxxxxx> wrote: >>>>>> >>>>>> Hi All, >>>>>> >>>>>> On 1/23/22 10:10, Tong Zhang wrote: >>>>>>> when acpi=off is provided in bootarg, kernel crash with >>>>>>> >>>>>>> [ 1.252739] BUG: kernel NULL pointer dereference, address: 0000000000000018 >>>>>>> [ 1.258308] Call Trace: >>>>>>> [ 1.258490] ? acpi_walk_namespace+0x147/0x147 >>>>>>> [ 1.258770] acpi_get_devices+0xe4/0x137 >>>>>>> [ 1.258921] ? drm_core_init+0xc0/0xc0 [drm] >>>>>>> [ 1.259108] detect_thinkpad_privacy_screen+0x5e/0xa8 [drm] >>>>>>> [ 1.259337] drm_privacy_screen_lookup_init+0xe/0xe85 [drm] >>>>>>> >>>>>>> The reason is that acpi_walk_namespace expects acpi related stuff >>>>>>> initialized but in fact it wouldn't when acpi is set to off. In this case >>>>>>> we should honor acpi=off in detect_thinkpad_privacy_screen(). >>>>>>> >>>>>>> Signed-off-by: Tong Zhang <ztong0001@xxxxxxxxx> >>>>>> >>>>>> Thank you for catching this and thank you for your patch. I was about to merge >>>>>> this, but then I realized that this might not be the best way to fix this. >>>>>> >>>>>> A quick grep shows 10 acpi_get_devices() calls outside of drivers/acpi, >>>>>> and at a first glance about half of those are missing an acpi_disabled >>>>>> check. IMHO it would be better to simply add an acpi_disabled check to >>>>>> acpi_get_devices() itself. >>>>>> >>>>>> Rafael, do you agree ? >>>>> >>>>> Yes, I do. >>>> >>>> Did you see my follow-up that that is not going to work because >>>> acpi_get_devices() is an acpica function ? >>> >>> No, I didn't, but it is possible to add a wrapper doing the check >>> around it and convert all of the users. >> >> Yes I did think about that. Note that I've gone ahead and pushed >> the fix which started this to drm-misc-fixes, to resolve the crash >> for now. > > OK > >> If we add such a wrapper we can remove a bunch of acpi_disabled checks >> from various callers. >> >>> Alternatively, the ACPICA function can check acpi_gbl_root_node >>> against NULL, like in the attached (untested) patch. >> >> That is probably an even better idea, as that avoids the need >> for a wrapper altogether. So I believe that that is the best >> solution. > > Allright, let me cut an analogous patch for the upstream ACPICA, then. Great, thank you. I have added a note about checking for when this has found its way into Linus' tree to my own TODO list, with the goal of doing a cleanup series removing the then no longer needed acpi_disabled checks in a bunch of places. Regards, Hans
