Re: acpi_get_devices() crash when acpi_disabled==true (was [PATCH v2] drm/privacy-screen: honor acpi=off in detect_thinkpad_privacy_screen)

[Hans de Goede]

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 ?

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)
>>
>