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drm/amdgpu: Fix fence put before wait in amdgpu_amdkfd_submit_ib

amdgpu_amdkfd_submit_ib() submits a GPU job and gets a fence
from amdgpu_ib_schedule(). This fence is used to wait for job
completion.

Currently, the code drops the fence reference using dma_fence_put()
before calling dma_fence_wait().

If dma_fence_put() releases the last reference, the fence may be
freed before dma_fence_wait() is called. This can lead to a
use-after-free.

Fix this by waiting on the fence first and releasing the reference
only after dma_fence_wait() completes.

Fixes the below:
drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.c:697 amdgpu_amdkfd_submit_ib() warn: passing freed memory 'f' (line 696)

Fixes: 9ae55f030dc5 ("drm/amdgpu: Follow up change to previous drm scheduler change.")
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: Dan Carpenter <dan.carpenter@linaro.org>
Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

authored by

Srinivasan Shanmugam and committed by
Alex Deucher 8b9e5259 47089160

+2 -2
+2 -2
drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.c
··· 692 692 goto err_ib_sched; 693 693 } 694 694 695 - /* Drop the initial kref_init count (see drm_sched_main as example) */ 696 - dma_fence_put(f); 697 695 ret = dma_fence_wait(f, false); 696 + /* Drop the returned fence reference after the wait completes */ 697 + dma_fence_put(f); 698 698 699 699 err_ib_sched: 700 700 amdgpu_job_free(job);