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 ?
Note the just added chrome privacy-screen check uses
acpi_dev_present(), this is also used in about 10 places outside
of drivers/acpi and AFAIK none of those do an acpi_disabled check.
acpi_dev_present() uses bus_find_device(&acpi_bus_type, ...)
but the acpi_bus_type does not get registered when acpi_disabled
is set. In the end this is fine though since bus_find_device
checks for the bus not being registered and then just returns
NULL.
Regards,
Hans
> ---
> v2: fix typo in previous commit -- my keyboard is eating letters
>
> drivers/gpu/drm/drm_privacy_screen_x86.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_privacy_screen_x86.c b/drivers/gpu/drm/drm_privacy_screen_x86.c
> index a2cafb294ca6..e7aa74ad0b24 100644
> --- a/drivers/gpu/drm/drm_privacy_screen_x86.c
> +++ b/drivers/gpu/drm/drm_privacy_screen_x86.c
> @@ -33,6 +33,9 @@ static bool __init detect_thinkpad_privacy_screen(void)
> unsigned long long output;
> acpi_status status;
>
> + if (acpi_disabled)
> + return false;
> +
> /* Get embedded-controller handle */
> status = acpi_get_devices("PNP0C09", acpi_set_handle, NULL, &ec_handle);
> if (ACPI_FAILURE(status) || !ec_handle)
