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Date:   Fri, 11 Jun 2021 14:38:18 +0200
From:   Christian König <christian.koenig@....com>
To:     Ondrej Zary <linux@...y.sk>
Cc:     Ben Skeggs <bskeggs@...hat.com>, dri-devel@...ts.freedesktop.org,
        nouveau@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: nouveau broken on Riva TNT2 in 5.13.0-rc4: NULL pointer
 dereference in nouveau_bo_sync_for_device



Am 10.06.21 um 19:59 schrieb Christian König:
> Am 10.06.21 um 19:50 schrieb Ondrej Zary:
>> [SNIP]
>>> I can't see how this is called from the nouveau code, only 
>>> possibility I
>>> see is that it is maybe called through the AGP code somehow.
>> Yes, you're right:
>> [   13.192663] Call Trace:
>> [   13.192678]  dump_stack+0x54/0x68
>> [   13.192690]  ttm_tt_init+0x11/0x8a [ttm]
>> [   13.192699]  ttm_agp_tt_create+0x39/0x51 [ttm]
>> [   13.192840]  nouveau_ttm_tt_create+0x17/0x22 [nouveau]
>> [   13.192856]  ttm_tt_create+0x78/0x8c [ttm]
>> [   13.192864]  ttm_bo_handle_move_mem+0x7d/0xca [ttm]
>> [   13.192873]  ttm_bo_validate+0x92/0xc8 [ttm]
>> [   13.192883]  ttm_bo_init_reserved+0x216/0x243 [ttm]
>> [   13.192892]  ttm_bo_init+0x45/0x65 [ttm]
>> [   13.193018]  ? nouveau_bo_del_io_reserve_lru+0x48/0x48 [nouveau]
>> [   13.193150]  nouveau_bo_init+0x8c/0x94 [nouveau]
>> [   13.193273]  ? nouveau_bo_del_io_reserve_lru+0x48/0x48 [nouveau]
>> [   13.193407]  nouveau_bo_new+0x44/0x57 [nouveau]
>> [   13.193537]  nouveau_channel_prep+0xa3/0x269 [nouveau]
>> [   13.193665]  nouveau_channel_new+0x3c/0x5f7 [nouveau]
>> [   13.193679]  ? slab_free_freelist_hook+0x3b/0xa7
>> [   13.193686]  ? kfree+0x9e/0x11a
>> [   13.193781]  ? nvif_object_sclass_put+0xd/0x16 [nouveau]
>> [   13.193908]  nouveau_drm_device_init+0x2e2/0x646 [nouveau]
>> [   13.193924]  ? pci_enable_device_flags+0x1e/0xac
>> [   13.194052]  nouveau_drm_probe+0xeb/0x188 [nouveau]
>> [   13.194182]  ? nouveau_drm_device_init+0x646/0x646 [nouveau]
>> [   13.194195]  pci_device_probe+0x89/0xe9
>> [   13.194205]  really_probe+0x127/0x2a7
>> [   13.194212]  driver_probe_device+0x5b/0x87
>> [   13.194219]  device_driver_attach+0x2e/0x41
>> [   13.194226]  __driver_attach+0x7c/0x83
>> [   13.194232]  bus_for_each_dev+0x4c/0x66
>> [   13.194238]  driver_attach+0x14/0x16
>> [   13.194244]  ? device_driver_attach+0x41/0x41
>> [   13.194251]  bus_add_driver+0xc5/0x16c
>> [   13.194258]  driver_register+0x87/0xb9
>> [   13.194265]  __pci_register_driver+0x38/0x3b
>> [   13.194271]  ? 0xf0c0d000
>> [   13.194362]  nouveau_drm_init+0x14c/0x1000 [nouveau]
>>
>> How is ttm_dma_tt->dma_address allocated?
>
> Mhm, I need to double check how AGP is supposed to work.
>
> Since barely anybody is using it these days it is something which 
> breaks from time to time.

I have no idea how that ever worked in the first place since AGP isn't 
supposed to sync between CPU/GPU. Everything is coherent for that case.

Anyway here is a patch which adds a check to those functions if the 
dma_address array is allocated in the first place. Please test it.

Thanks,
Christian.

>
> Thanks for the backtrace,
> Christian.
>
>>   I cannot find any assignment
>> executed (in the working code):
>>
>> $ git grep dma_address\ = drivers/gpu/
>> drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c: 
>> sg->sgl->dma_address = addr;
>> drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c: dma_address = 
>> &dma->dma_address[offset >> PAGE_SHIFT];
>> drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c: dma_address = 
>> (mm_node->start << PAGE_SHIFT) + offset;
>> drivers/gpu/drm/i915/gvt/scheduler.c:   sg->dma_address = addr;
>> drivers/gpu/drm/i915/i915_gpu_error.c:  sg->dma_address = it;
>> drivers/gpu/drm/ttm/ttm_tt.c:   ttm->dma_address = (void *) 
>> (ttm->ttm.pages + ttm->ttm.num_pages);
>> drivers/gpu/drm/ttm/ttm_tt.c:   ttm->dma_address = 
>> kvmalloc_array(ttm->ttm.num_pages,
>> drivers/gpu/drm/ttm/ttm_tt.c:   ttm_dma->dma_address = NULL;
>> drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c: viter->dma_address = 
>> &__vmw_piter_phys_addr;
>> drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c: viter->dma_address = 
>> &__vmw_piter_dma_addr;
>> drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c: viter->dma_address = 
>> &__vmw_piter_sg_addr;
>>
>> The 2 cases in ttm_tt.c are in ttm_dma_tt_alloc_page_directory() and
>> ttm_sg_tt_alloc_page_directory().
>> Confirmed by adding printk()s that they're NOT called.
>>
>>
>


View attachment "0001-drm-nouveau-check-dma_address-array-for-CPU-GPU-sync.patch" of type "text/x-patch" (1364 bytes)

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