* [PATCH] Revert "drm/tegra: Use dma_buf from GEM object instance"
@ 2025-07-15 8:45 Thomas Zimmermann
2025-07-15 13:16 ` Simona Vetter
2025-08-12 9:12 ` Thomas Zimmermann
0 siblings, 2 replies; 4+ messages in thread
From: Thomas Zimmermann @ 2025-07-15 8:45 UTC (permalink / raw)
To: thierry.reding, mperttunen, airlied, simona, jonathanh
Cc: linux-tegra, dri-devel, Thomas Zimmermann
This reverts commit 482c7e296edc0f594e8869a789a40be53c49bd6a.
The dma_buf field in struct drm_gem_object is not stable over the
object instance's lifetime. The field becomes NULL when user space
releases the final GEM handle on the buffer object. This resulted
in a NULL-pointer deref.
Workarounds in commit 5307dce878d4 ("drm/gem: Acquire references on
GEM handles for framebuffers") and commit f6bfc9afc751 ("drm/framebuffer:
Acquire internal references on GEM handles") only solved the problem
partially. They especially don't work for buffer objects without a DRM
framebuffer associated.
Hence, this revert to going back to using .import_attach->dmabuf.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---
drivers/gpu/drm/tegra/gem.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
index 41a285ec889f..8ede07fb7a21 100644
--- a/drivers/gpu/drm/tegra/gem.c
+++ b/drivers/gpu/drm/tegra/gem.c
@@ -526,7 +526,7 @@ void tegra_bo_free_object(struct drm_gem_object *gem)
if (drm_gem_is_imported(gem)) {
dma_buf_unmap_attachment_unlocked(gem->import_attach, bo->sgt,
DMA_TO_DEVICE);
- dma_buf_detach(gem->dma_buf, gem->import_attach);
+ dma_buf_detach(gem->import_attach->dmabuf, gem->import_attach);
}
}
--
2.50.0
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH] Revert "drm/tegra: Use dma_buf from GEM object instance"
2025-07-15 8:45 [PATCH] Revert "drm/tegra: Use dma_buf from GEM object instance" Thomas Zimmermann
@ 2025-07-15 13:16 ` Simona Vetter
2025-08-12 9:12 ` Thomas Zimmermann
1 sibling, 0 replies; 4+ messages in thread
From: Simona Vetter @ 2025-07-15 13:16 UTC (permalink / raw)
To: Thomas Zimmermann
Cc: thierry.reding, mperttunen, airlied, simona, jonathanh,
linux-tegra, dri-devel
On Tue, Jul 15, 2025 at 10:45:39AM +0200, Thomas Zimmermann wrote:
> This reverts commit 482c7e296edc0f594e8869a789a40be53c49bd6a.
>
> The dma_buf field in struct drm_gem_object is not stable over the
> object instance's lifetime. The field becomes NULL when user space
> releases the final GEM handle on the buffer object. This resulted
> in a NULL-pointer deref.
>
> Workarounds in commit 5307dce878d4 ("drm/gem: Acquire references on
> GEM handles for framebuffers") and commit f6bfc9afc751 ("drm/framebuffer:
> Acquire internal references on GEM handles") only solved the problem
> partially. They especially don't work for buffer objects without a DRM
> framebuffer associated.
>
> Hence, this revert to going back to using .import_attach->dmabuf.
>
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch>
> ---
> drivers/gpu/drm/tegra/gem.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
> index 41a285ec889f..8ede07fb7a21 100644
> --- a/drivers/gpu/drm/tegra/gem.c
> +++ b/drivers/gpu/drm/tegra/gem.c
> @@ -526,7 +526,7 @@ void tegra_bo_free_object(struct drm_gem_object *gem)
> if (drm_gem_is_imported(gem)) {
> dma_buf_unmap_attachment_unlocked(gem->import_attach, bo->sgt,
> DMA_TO_DEVICE);
> - dma_buf_detach(gem->dma_buf, gem->import_attach);
> + dma_buf_detach(gem->import_attach->dmabuf, gem->import_attach);
> }
> }
>
> --
> 2.50.0
>
--
Simona Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] Revert "drm/tegra: Use dma_buf from GEM object instance"
2025-07-15 8:45 [PATCH] Revert "drm/tegra: Use dma_buf from GEM object instance" Thomas Zimmermann
2025-07-15 13:16 ` Simona Vetter
@ 2025-08-12 9:12 ` Thomas Zimmermann
2025-08-26 8:40 ` Thomas Zimmermann
1 sibling, 1 reply; 4+ messages in thread
From: Thomas Zimmermann @ 2025-08-12 9:12 UTC (permalink / raw)
To: thierry.reding, mperttunen, airlied, simona, jonathanh
Cc: linux-tegra, dri-devel
Hi Thierry,
can I take this patch into drm-misc-fixes?
Best regards
Thomas
Am 15.07.25 um 10:45 schrieb Thomas Zimmermann:
> This reverts commit 482c7e296edc0f594e8869a789a40be53c49bd6a.
>
> The dma_buf field in struct drm_gem_object is not stable over the
> object instance's lifetime. The field becomes NULL when user space
> releases the final GEM handle on the buffer object. This resulted
> in a NULL-pointer deref.
>
> Workarounds in commit 5307dce878d4 ("drm/gem: Acquire references on
> GEM handles for framebuffers") and commit f6bfc9afc751 ("drm/framebuffer:
> Acquire internal references on GEM handles") only solved the problem
> partially. They especially don't work for buffer objects without a DRM
> framebuffer associated.
>
> Hence, this revert to going back to using .import_attach->dmabuf.
>
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> ---
> drivers/gpu/drm/tegra/gem.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
> index 41a285ec889f..8ede07fb7a21 100644
> --- a/drivers/gpu/drm/tegra/gem.c
> +++ b/drivers/gpu/drm/tegra/gem.c
> @@ -526,7 +526,7 @@ void tegra_bo_free_object(struct drm_gem_object *gem)
> if (drm_gem_is_imported(gem)) {
> dma_buf_unmap_attachment_unlocked(gem->import_attach, bo->sgt,
> DMA_TO_DEVICE);
> - dma_buf_detach(gem->dma_buf, gem->import_attach);
> + dma_buf_detach(gem->import_attach->dmabuf, gem->import_attach);
> }
> }
>
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] Revert "drm/tegra: Use dma_buf from GEM object instance"
2025-08-12 9:12 ` Thomas Zimmermann
@ 2025-08-26 8:40 ` Thomas Zimmermann
0 siblings, 0 replies; 4+ messages in thread
From: Thomas Zimmermann @ 2025-08-26 8:40 UTC (permalink / raw)
To: thierry.reding, mperttunen, airlied, simona, jonathanh
Cc: linux-tegra, dri-devel
Hi
Am 12.08.25 um 11:12 schrieb Thomas Zimmermann:
> Hi Thierry,
>
> can I take this patch into drm-misc-fixes?
I'm merging this patch into drm-misc-fixes to get the upstream bug fixed.
Best regards
Thomas
>
> Best regards
> Thomas
>
> Am 15.07.25 um 10:45 schrieb Thomas Zimmermann:
>> This reverts commit 482c7e296edc0f594e8869a789a40be53c49bd6a.
>>
>> The dma_buf field in struct drm_gem_object is not stable over the
>> object instance's lifetime. The field becomes NULL when user space
>> releases the final GEM handle on the buffer object. This resulted
>> in a NULL-pointer deref.
>>
>> Workarounds in commit 5307dce878d4 ("drm/gem: Acquire references on
>> GEM handles for framebuffers") and commit f6bfc9afc751
>> ("drm/framebuffer:
>> Acquire internal references on GEM handles") only solved the problem
>> partially. They especially don't work for buffer objects without a DRM
>> framebuffer associated.
>>
>> Hence, this revert to going back to using .import_attach->dmabuf.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>> ---
>> drivers/gpu/drm/tegra/gem.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
>> index 41a285ec889f..8ede07fb7a21 100644
>> --- a/drivers/gpu/drm/tegra/gem.c
>> +++ b/drivers/gpu/drm/tegra/gem.c
>> @@ -526,7 +526,7 @@ void tegra_bo_free_object(struct drm_gem_object
>> *gem)
>> if (drm_gem_is_imported(gem)) {
>> dma_buf_unmap_attachment_unlocked(gem->import_attach, bo->sgt,
>> DMA_TO_DEVICE);
>> - dma_buf_detach(gem->dma_buf, gem->import_attach);
>> + dma_buf_detach(gem->import_attach->dmabuf,
>> gem->import_attach);
>> }
>> }
>
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)
^ permalink raw reply [flat|nested] 4+ messages in thread
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2025-07-15 8:45 [PATCH] Revert "drm/tegra: Use dma_buf from GEM object instance" Thomas Zimmermann
2025-07-15 13:16 ` Simona Vetter
2025-08-12 9:12 ` Thomas Zimmermann
2025-08-26 8:40 ` Thomas Zimmermann
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