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. 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. Regards, Hans
