There is one one corner case at dma_fence_signal_locked which will raise the NULL pointer problem just like below. ->dma_fence_signal ->dma_fence_signal_locked ->test_and_set_bit here trigger dma_fence_release happen due to the zero of fence refcount.
->dma_fence_put ->dma_fence_release ->drm_sched_fence_release_scheduled ->call_rcu here make the union fled “cb_list” at finished fence to NULL because struct rcu_head contains two pointer which is same as struct list_head cb_list
Therefore, to hold the reference of finished fence at drm_sched_process_job to prevent the null pointer during finished fence dma_fence_signal
[ 732.912867] BUG: kernel NULL pointer dereference, address: 0000000000000008 [ 732.914815] #PF: supervisor write access in kernel mode [ 732.915731] #PF: error_code(0x0002) - not-present page [ 732.916621] PGD 0 P4D 0 [ 732.917072] Oops: 0002 [#1] SMP PTI [ 732.917682] CPU: 7 PID: 0 Comm: swapper/7 Tainted: G OE 5.4.0-rc7 #1 [ 732.918980] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.2-0-g33fbe13 by qemu-project.org 04/01/2014 [ 732.920906] RIP: 0010:dma_fence_signal_locked+0x3e/0x100 [ 732.938569] Call Trace: [ 732.939003] <IRQ> [ 732.939364] dma_fence_signal+0x29/0x50 [ 732.940036] drm_sched_fence_finished+0x12/0x20 [gpu_sched] [ 732.940996] drm_sched_process_job+0x34/0xa0 [gpu_sched] [ 732.941910] dma_fence_signal_locked+0x85/0x100 [ 732.942692] dma_fence_signal+0x29/0x50 [ 732.943457] amdgpu_fence_process+0x99/0x120 [amdgpu] [ 732.944393] sdma_v4_0_process_trap_irq+0x81/0xa0 [amdgpu]
v2: hold the finished fence at drm_sched_process_job instead of amdgpu_fence_process v3: resume the blank line
Signed-off-by: Yintian Tao yttao@amd.com Reviewed-by: Christian König christian.koenig@amd.com --- drivers/gpu/drm/scheduler/sched_main.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c index a18eabf692e4..8e731ed0d9d9 100644 --- a/drivers/gpu/drm/scheduler/sched_main.c +++ b/drivers/gpu/drm/scheduler/sched_main.c @@ -651,7 +651,9 @@ static void drm_sched_process_job(struct dma_fence *f, struct dma_fence_cb *cb)
trace_drm_sched_process_job(s_fence);
+ dma_fence_get(&s_fence->finished); drm_sched_fence_finished(s_fence); + dma_fence_put(&s_fence->finished); wake_up_interruptible(&sched->wake_up_worker); }