Hi
Am 15.04.25 um 14:52 schrieb Christian König:
Am 15.04.25 um 14:40 schrieb Thomas Zimmermann:
Hi
Am 15.04.25 um 14:19 schrieb Christian König:
Am 15.04.25 um 12:45 schrieb Thomas Zimmermann:
Hi
Am 15.04.25 um 11:39 schrieb Christian König:
Am 15.04.25 um 11:20 schrieb Thomas Zimmermann:
Test struct drm_gem_object.import_attach to detect imported objects
during cleanup. At that point, the imported DMA buffer might have
already been released and the dma_buf field is NULL. The object's
free callback then does a cleanup as for native objects.
I don't think that this is a good idea.
The DMA-buf is separately reference counted through the import attachment.
I understand that it's not ideal, but testing for import_attach to be set is
what we currently do throughout drivers. Putting this behind an interface is
already a step forward.
Happens for calls to drm_mode_destroy_dumb_ioctl() that eventually
clear the dma_buf field in drm_gem_object_exported_dma_buf_free().
That is for exported DMA-buf and should *NEVER* be used for imported ones.
Did you look at the discussion at the Closes tag? Where else could dma-buf be
cleared?
Yeah, I've seen that. The solution is just completely wrong.
See for the export case obj->dma_buf points to the exported DMA-buf and causes
a circle dependency when not set to NULL when the last handle is released.
But for the import case obj->dma_buf is actually not that relevant. Instead
obj->import_attach->dma_buf should be used.
So if I understand correctly, the tests in that helper should be done by looking
at import_attach->dma_buf.
At least in theory yes. IIRC we also set obj->dma_buf to the same value as
import_attach->dma_buf for convenient so that code doesn't need to check both.
But it can be that obj->dma_buf is already NULL while the import attachment is still
in the process of being cleaned up. So there are a couple of cases where we have to look
at obj->import_attach->dma_buf.
Ok, that should also solve the problem for now. The point here is to
limit exposure of import_attach.
The long-term goal is to make import_attach optional because its setup requires
a DMA-capable device.
HUI WHAT?
Dmitry and I put quite some effort into being able to create an import_attach
without the requirement to have a DMA-capable device.
The last puzzle piece of that landed a month ago in the form of this patch here:
commit b72f66f22c0e39ae6684c43fead774c13db24e73
Author: Christian König <christian.koe...@amd.com>
Date: Tue Feb 11 17:20:53 2025 +0100
dma-buf: drop caching of sg_tables
That was purely for the transition from static to dynamic dma-buf
handling and can be removed again now.
Signed-off-by: Christian König <christian.koe...@amd.com>
Reviewed-by: Simona Vetter <simona.vet...@ffwll.ch>
Reviewed-by: Dmitry Osipenko <dmitry.osipe...@collabora.com>
Link:
https://patchwork.freedesktop.org/patch/msgid/20250211163109.12200-5-christian.koe...@amd.com
When you don't create an import attachment the exporter wouldn't know that his
buffer is actually used which is usually a quite bad idea.
This is for devices who only want to do a vmap of the buffer, isn't it?
Yeah, the vmap needs the sgtable, which needs import_attach IIRC.
Somewhere in there a DMA device is required. But it's not of high
priority as we have workarounds.
Best regards
Thomas
Regards,
Christian.
Best regards
Thomas
Regards,
Christian.
Best regards
Thomas
Regards,
Christian.
Signed-off-by: Thomas Zimmermann <tzimmerm...@suse.de>
Fixes: b57aa47d39e9 ("drm/gem: Test for imported GEM buffers with helper")
Reported-by: Andy Yan <andys...@163.com>
Closes:
https://lore.kernel.org/dri-devel/38d09d34.4354.196379aa560.coremail.andys...@163.com/
Tested-by: Andy Yan <andys...@163.com>
Cc: Thomas Zimmermann <tzimmerm...@suse.de>
Cc: Anusha Srivatsa <asriv...@redhat.com>
Cc: Christian König <christian.koe...@amd.com>
Cc: Maarten Lankhorst <maarten.lankho...@linux.intel.com>
Cc: Maxime Ripard <mrip...@kernel.org>
Cc: David Airlie <airl...@gmail.com>
Cc: Simona Vetter <sim...@ffwll.ch>
Cc: Sumit Semwal <sumit.sem...@linaro.org>
Cc: "Christian König" <christian.koe...@amd.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-me...@vger.kernel.org
Cc: linaro-mm-...@lists.linaro.org
---
include/drm/drm_gem.h | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index 9b71f7a9f3f8..f09b8afcf86d 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -589,7 +589,13 @@ static inline bool
drm_gem_object_is_shared_for_memory_stats(struct drm_gem_obje
static inline bool drm_gem_is_imported(const struct drm_gem_object *obj)
{
/* The dma-buf's priv field points to the original GEM object. */
- return obj->dma_buf && (obj->dma_buf->priv != obj);
+ return (obj->dma_buf && (obj->dma_buf->priv != obj)) ||
+ /*
+ * TODO: During object release, the dma-buf might already
+ * be gone. For now keep testing import_attach, but
+ * this should be removed at some point.
+ */
+ obj->import_attach;
}
#ifdef CONFIG_LOCKDEP
--
--
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)
