On 10/10/26 20:07, Julian Orth wrote:
A sync_file exported from a timeline point can contain a dma_fence_chain.
No it can't, IIRC sync files are only supposed to contain raw fences or dma_fence_array containers.
I think we never documented that and that's why this issue here leaked in.
I'm not sure if that doesn't break anywhere else as well, so I think we should fix the exporting side instead.
Alternatively we need to audit everywhere where fences from syncfiles can be imported somewhere else.
Regards, Christian.
Importing such a sync_file into a timeline point with DRM_SYNCOBJ_FD_TO_HANDLE_FLAGS_IMPORT_SYNC_FILE | DRM_SYNCOBJ_FD_TO_HANDLE_FLAGS_TIMELINE passes the chain directly to dma_fence_chain_init() and triggers
WARNING: drivers/dma-buf/dma-fence-chain.c:286 at dma_fence_chain_init
because chain fences must not be wrapped in other chain fences.
Flatten the fence with dma_fence_unwrap_merge() before adding it to the timeline, as drm_syncobj_transfer_to_timeline() already does.
Reproducer:
- Export a sync_file from a point > 0 of a timeline syncobj with DRM_IOCTL_SYNCOBJ_HANDLE_TO_FD.
- Import it into a point > 0 of another timeline syncobj with DRM_IOCTL_SYNCOBJ_FD_TO_HANDLE.
Fixes: c2d3a7300695 ("drm/syncobj: Extend EXPORT_SYNC_FILE for timeline syncobjs") Assisted-by: Claude:claude-opus-5-5 Signed-off-by: Julian Orth ju.orth@gmail.com
drivers/gpu/drm/drm_syncobj.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c index 5ca5163d0..c545af77e 100644 --- a/drivers/gpu/drm/drm_syncobj.c +++ b/drivers/gpu/drm/drm_syncobj.c @@ -742,8 +742,18 @@ static int drm_syncobj_import_sync_file_fence(struct drm_file *file_private, } if (point) {
struct dma_fence_chain *chain = dma_fence_chain_alloc();
struct dma_fence_chain *chain;struct dma_fence *tmp;tmp = dma_fence_unwrap_merge(fence);dma_fence_put(fence);fence = tmp;if (!fence) {drm_syncobj_put(syncobj);return -ENOMEM;}
chain = dma_fence_chain_alloc();