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From:   Ondrej Zary <linux@zary.sk>
To:     Christian =?utf-8?q?K=C3=B6nig?= <christian.koenig@amd.com>
Subject: Re: nouveau broken on Riva TNT2 in 5.13.0-rc4: NULL pointer dereference in nouveau_bo_sync_for_device
Date:   Wed, 9 Jun 2021 22:00:07 +0200
User-Agent: KMail/1.9.10
Cc:     Ben Skeggs <bskeggs@redhat.com>, dri-devel@lists.freedesktop.org,
        nouveau@lists.freedesktop.org, linux-kernel@vger.kernel.org
References: <202106052143.52488.linux@zary.sk> <202106090910.51188.linux@zary.sk> <762c1044-6e3a-48fc-95e4-1730b6ef2a2e@amd.com>
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On Wednesday 09 June 2021 11:21:05 Christian König wrote:
> Am 09.06.21 um 09:10 schrieb Ondrej Zary:
> > On Wednesday 09 June 2021, Christian König wrote:
> >> Am 09.06.21 um 08:57 schrieb Ondrej Zary:
> >>> [SNIP]
> >>>> Thanks for the heads up. So the problem with my patch is already fixed,
> >>>> isn't it?
> >>> The NULL pointer dereference in nouveau_bo_wr16 introduced in
> >>> 141b15e59175aa174ca1f7596188bd15a7ca17ba was fixed by
> >>> aea656b0d05ec5b8ed5beb2f94c4dd42ea834e9d.
> >>>
> >>> That's the bug I hit when bisecting the original problem:
> >>> NULL pointer dereference in nouveau_bo_sync_for_device
> >>> It's caused by:
> >>> # first bad commit: [e34b8feeaa4b65725b25f49c9b08a0f8707e8e86] drm/ttm: merge ttm_dma_tt back into ttm_tt
> >> Good that I've asked :)
> >>
> >> Ok that's a bit strange. e34b8feeaa4b65725b25f49c9b08a0f8707e8e86 was
> >> created mostly automated.
> >>
> >> Do you have the original backtrace of that NULL pointer deref once more?
> > The original backtrace is here: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.org%2Flkml%2F2021%2F6%2F5%2F350&amp;data=04%7C01%7Cchristian.koenig%40amd.com%7Ce905b6bd2aa842ace15508d92b15b96d%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637588195000729460%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=zFqheBbJcOHtYgqG%2Fs63AT1dwuk4REmUDJWHvzaLAlc%3D&amp;reserved=0
> 
> And the problem is that ttm_dma->dma_address is NULL, right? Mhm, I 
> don't see how that can happen since nouveau is using ttm_sg_tt_init().
> 
> Apart from that what nouveau does here is rather questionable since you 
> need a coherent architecture for most things anyway, but that's not what 
> we are trying to fix here.
> 
> Can you try to narrow down if ttm_sg_tt_init is called before calling 
> this function for the tt object in question?

ttm_sg_tt_init is not called:
[   12.150124] nouveau 0000:01:00.0: DRM: VRAM: 31 MiB
[   12.150133] nouveau 0000:01:00.0: DRM: GART: 128 MiB
[   12.150143] nouveau 0000:01:00.0: DRM: BMP version 5.6
[   12.150151] nouveau 0000:01:00.0: DRM: No DCB data found in VBIOS
[   12.151362] ttm_tt_init
[   12.151370] ttm_tt_init_fields
[   12.151374] ttm_tt_alloc_page_directory
[   12.151615] BUG: kernel NULL pointer dereference, address: 00000000


-- 
Ondrej Zary