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 14:47, 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 <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 ?

Never mind I just saw that acpi_get_devices() is part of acpica, where
as the acpi_disabled flag is not. So callers need to check acpi_disabled
before calling acpi_get_devices().

I'll go and push this patch to drm-misc-fixes now.

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)