[5.12 regression] ttm->pages NULL dereference with radeon driver

[Christian König]

Hi guys,

adding a few people who ran into the problem as well and opened a kernel 
bug.

Am 07.05.21 um 17:11 schrieb Christian König:
> Hi Takashi,
>
> Am 07.05.21 um 17:08 schrieb Takashi Iwai:
>> Hi,
>>
>> we've received a regression report showing NULL dereference Oops with
>> radeon driver on 5.12 kernel:
>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.opensuse.org%2Fshow_bug.cgi%3Fid%3D1185516&data=04%7C01%7Cchristian.koenig%40amd.com%7C64447e9e97604aaf117008d9116a742a%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637559971181187178%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=1LJMLxuuMjkfgnIt%2B5Z5n19ri%2BMTLMQvEEB%2F%2Fd6SVkg%3D&reserved=0
>>
>> It turned out that the recent TTM cleanup / refactoring via commit
>> 0575ff3d33cd ("drm/radeon: stop using pages with
>> drm_prime_sg_to_page_addr_arrays v2") is the culprit.  On 5.12 kernel,
>> ttm->pages is no longer allocated / set up, while the radeon driver
>> still has a few places assuming the valid ttm->pages, and for the
>> reporter (running the modesettig driver), radeon_gart_bind() hits the
>> problem.
>>
>> A hackish patch below was confirmed to work, at least, but obviously
>> we need a proper fix.
>>
>> Could you take a look at it?
>
> If that's all then that looks trivial to me.
>
> Going to provide a patch on Monday.

Sorry, was a busy start into the week. I've just send a patch which 
should address the issue to you and the mailing list.

Please test since I can't reproduce the problem locally.

Thanks,
Christian.

>
> Thanks for the notice,
> Christian.
>
>>
>>
>> thanks,
>>
>> Takashi
>>
>> --- a/drivers/gpu/drm/radeon/radeon_gart.c
>> +++ b/drivers/gpu/drm/radeon/radeon_gart.c
>> @@ -253,7 +253,7 @@ void radeon_gart_unbind(struct radeon_de
>>       t = offset / RADEON_GPU_PAGE_SIZE;
>>       p = t / (PAGE_SIZE / RADEON_GPU_PAGE_SIZE);
>>       for (i = 0; i < pages; i++, p++) {
>> -        if (rdev->gart.pages[p]) {
>> +        if (1 /*rdev->gart.pages[p]*/) {
>>               rdev->gart.pages[p] = NULL;
>>               for (j = 0; j < (PAGE_SIZE / RADEON_GPU_PAGE_SIZE); 
>> j++, t++) {
>>                   rdev->gart.pages_entry[t] = rdev->dummy_page.entry;
>> @@ -301,7 +301,7 @@ int radeon_gart_bind(struct radeon_devic
>>       p = t / (PAGE_SIZE / RADEON_GPU_PAGE_SIZE);
>>         for (i = 0; i < pages; i++, p++) {
>> -        rdev->gart.pages[p] = pagelist[i];
>> +        /* rdev->gart.pages[p] = pagelist[i]; */
>>           page_base = dma_addr[i];
>>           for (j = 0; j < (PAGE_SIZE / RADEON_GPU_PAGE_SIZE); j++, 
>> t++) {
>>               page_entry = radeon_gart_get_page_entry(page_base, flags);
>> --- a/drivers/gpu/drm/radeon/radeon_ttm.c
>> +++ b/drivers/gpu/drm/radeon/radeon_ttm.c
>> @@ -360,6 +360,8 @@ static int radeon_ttm_tt_pin_userptr(str
>>         if (current->mm != gtt->usermm)
>>           return -EPERM;
>> +    if (!ttm->pages)
>> +        return -EPERM;
>>         if (gtt->userflags & RADEON_GEM_USERPTR_ANONONLY) {
>>           /* check that we only pin down anonymous memory
>> _______________________________________________
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>>
>