On Wed, Jan 26, 2022 at 5:41 PM Hans de Goede wrote: > > Hi, > > On 1/26/22 16:54, Rafael J. Wysocki wrote: > > On Wed, Jan 26, 2022 at 2:47 PM Hans de Goede 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 > >> > >> 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. Alternatively, the ACPICA function can check acpi_gbl_root_node against NULL, like in the attached (untested) patch.