I've just double checked and your analyses actually can't be correct.
When we call dma_fence_signal() in amdgpu_fence_process() we still have
a reference to the fence.
See the code here:
r = dma_fence_signal(fence);
if (!r)
DMA_FENCE_TRACE(fence, "signaled from irq
context\n");
else
BUG();
dma_fence_put(fence);
So I'm not sure how you ran into the crash in the first place, this is
most likely something else.
Regards,
Christian.
Am 23.03.20 um 12:49 schrieb Yintian Tao:
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 amdgpu_job_run
to prevent the null pointer during 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]
Signed-off-by: Yintian Tao <yttao@xxxxxxx>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c | 19 ++++++++++++++++++-
drivers/gpu/drm/amd/amdgpu/amdgpu_job.c | 2 ++
drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h | 3 +++
3 files changed, 23 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
index 7531527067df..03573eff660a 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
@@ -52,7 +52,7 @@
struct amdgpu_fence {
struct dma_fence base;
-
+ struct dma_fence *finished;
/* RB, DMA, etc. */
struct amdgpu_ring *ring;
};
@@ -149,6 +149,7 @@ int amdgpu_fence_emit(struct amdgpu_ring *ring, struct dma_fence **f,
seq = ++ring->fence_drv.sync_seq;
fence->ring = ring;
+ fence->finished = NULL;
dma_fence_init(&fence->base, &amdgpu_fence_ops,
&ring->fence_drv.lock,
adev->fence_context + ring->idx,
@@ -182,6 +183,21 @@ int amdgpu_fence_emit(struct amdgpu_ring *ring, struct dma_fence **f,
return 0;
}
+void amdgpu_fence_get_finished(struct dma_fence *base,
+ struct dma_fence *finished)
+{
+ struct amdgpu_fence *afence = to_amdgpu_fence(base);
+
+ afence->finished = dma_fence_get(finished);
+}
+
+void amdgpu_fence_put_finished(struct dma_fence *base)
+{
+ struct amdgpu_fence *afence = to_amdgpu_fence(base);
+
+ dma_fence_put(afence->finished);
+}
+
/**
* amdgpu_fence_emit_polling - emit a fence on the requeste ring
*
@@ -276,6 +292,7 @@ bool amdgpu_fence_process(struct amdgpu_ring *ring)
BUG();
dma_fence_put(fence);
+ amdgpu_fence_put_finished(fence);
pm_runtime_mark_last_busy(adev->ddev->dev);
pm_runtime_put_autosuspend(adev->ddev->dev);
} while (last_seq != seq);
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
index 4981e443a884..deb2aeeadfb3 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
@@ -229,6 +229,8 @@ static struct dma_fence *amdgpu_job_run(struct drm_sched_job *sched_job)
&fence);
if (r)
DRM_ERROR("Error scheduling IBs (%d)\n", r);
+ else
+ amdgpu_fence_get_finished(fence, finished);
}
/* if gpu reset, hw fence will be replaced here */
dma_fence_put(job->fence);
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h
index 448c76cbf3ed..fd4da91859aa 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h
@@ -96,6 +96,9 @@ void amdgpu_fence_driver_suspend(struct amdgpu_device *adev);
void amdgpu_fence_driver_resume(struct amdgpu_device *adev);
int amdgpu_fence_emit(struct amdgpu_ring *ring, struct dma_fence **fence,
unsigned flags);
+void amdgpu_fence_get_finished(struct dma_fence *base,
+ struct dma_fence *finished);
+void amdgpu_fence_put_finished(struct dma_fence *base);
int amdgpu_fence_emit_polling(struct amdgpu_ring *ring, uint32_t *s);
bool amdgpu_fence_process(struct amdgpu_ring *ring);
int amdgpu_fence_wait_empty(struct amdgpu_ring *ring);
_______________________________________________
amd-gfx mailing list
amd-gfx@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/amd-gfx
