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Drivers that can delegate waits to the firmware/GPU pass the scheduled fence to drm_sched_job_add_dependency(), and issue wait commands to the firmware/GPU at job submission time. For this to be possible, they need all their 'native' dependencies to have a valid parent since this is where the actual HW fence information are encoded. In drm_sched_main(), we currently call drm_sched_fence_set_parent() after drm_sched_fence_scheduled(), leaving a short period of time during which the job depending on this fence can be submitted. Since setting parent and signaling the fence are two things that are kinda related (you can't have a parent if the job hasn't been scheduled), it probably makes sense to pass the parent fence to drm_sched_fence_scheduled() and let it call drm_sched_fence_set_parent() before it signals the scheduled fence. Here is a detailed description of the race we are fixing here: Thread A Thread B - calls drm_sched_fence_scheduled() - signals s_fence->scheduled which wakes up thread B - entity dep signaled, checking the next dep - no more deps waiting - entity is picked for job submission by drm_gpu_scheduler - run_job() is called - run_job() tries to collect native fence info from s_fence->parent, but it's NULL => BOOM, we can't do our native wait - calls drm_sched_fence_set_parent() v2: * Fix commit message v3: * Add a detailed description of the race to the commit message * Add Luben's R-b Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com> Cc: Frank Binns <frank.binns@imgtec.com> Cc: Sarah Walker <sarah.walker@imgtec.com> Cc: Donald Robson <donald.robson@imgtec.com> Cc: Luben Tuikov <luben.tuikov@amd.com> Cc: David Airlie <airlied@gmail.com> Cc: Daniel Vetter <daniel@ffwll.ch> Cc: Sumit Semwal <sumit.semwal@linaro.org> Cc: "Christian König" <christian.koenig@amd.com> Reviewed-by: Luben Tuikov <luben.tuikov@amd.com> Link: https://patchwork.freedesktop.org/patch/msgid/20230623075204.382350-1-boris.brezillon@collabora.com
Linux kernel
============
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In order to build the documentation, use ``make htmldocs`` or
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