Re: [PATCH] drm/amdgpu: change the fence ring wait timeout

["Christian König" <christian.koenig@amd.com>]

Mhm, we could change amdgpu_fence_wait_empty() to timeout. But I think 
that waiting forever here is intentional and the right thing to do.

What happens is that we wait for the hardware to make sure that nothing 
is writing to any memory before we unload the driver.

Now the VCN block has crashed and doesn't respond, but we can't 
guarantee that it is not accidentally writing anywhere.

The only alternative we have is to time out and proceed with the driver 
unload, risking corrupting the memory we free during that should the 
hardware continue to do something.

Regards,
Christian.

Am 18.01.21 um 03:01 schrieb Deng, Emily:
> [AMD Official Use Only - Internal Distribution Only]
>
>> -----Original Message-----
>> From: Koenig, Christian <Christian.Koenig@amd.com>
>> Sent: Thursday, January 14, 2021 9:50 PM
>> To: Deng, Emily <Emily.Deng@amd.com>; Sun, Roy <Roy.Sun@amd.com>;
>> amd-gfx@lists.freedesktop.org
>> Subject: Re: [PATCH] drm/amdgpu: change the fence ring wait timeout
>>
>> Am 14.01.21 um 03:00 schrieb Deng, Emily:
>>> [AMD Official Use Only - Internal Distribution Only]
>>>
>>>> -----Original Message-----
>>>> From: amd-gfx <amd-gfx-bounces@lists.freedesktop.org> On Behalf Of
>>>> Christian König
>>>> Sent: Wednesday, January 13, 2021 10:03 PM
>>>> To: Sun, Roy <Roy.Sun@amd.com>; amd-gfx@lists.freedesktop.org
>>>> Subject: Re: [PATCH] drm/amdgpu: change the fence ring wait timeout
>>>>
>>>> Am 13.01.21 um 07:36 schrieb Roy Sun:
>>>>> This fix bug where when the engine hang, the fence ring will wait
>>>>> without quit and cause kernel crash
>>>> NAK, this blocking is intentional unlimited because otherwise we will
>>>> cause a memory corruption.
>>>>
>>>> What is the actual bug you are trying to fix here?
>>> When some engine hang during initialization, the IB test will fail,
>>> and fence will never come back, then never could wait the fence back.
>>> Why we need to wait here forever? We'd better not use forever wait which
>> will cause kernel crash and lockup. And we have
>> amdgpu_fence_driver_force_completion will let memory free. We should
>> remove all those forever wait, and replace them with one timeout,  and do
>> the correct error process if timeout.
>>
>> This wait here is to make sure we never overwrite the software fence ring
>> buffer. Without it we would not signal all fences in
>> amdgpu_fence_driver_force_completion() and cause either memory leak or
>> corruption.
>>
>> Waiting here forever is the right thing to do even when that means that the
>> submission thread gets stuck forever, cause that is still better than memory
>> corruption.
>>
>> But this should never happen in practice and is only here for precaution. So do
>> you really see that in practice?
> Yes, we hit the issue when vcn ib test fail. Could you give some suggestions about how to fix this?
> [  958.301685] failed to read reg:1a6c0
>
> [  959.036645] gmc_v10_0_process_interrupt: 42 callbacks suppressed
>
> [  959.036653] amdgpu 0000:00:07.0: [mmhub] page fault (src_id:0 ring:0 vmid:0 pasid:0, for process  pid 0 thread  pid 0)
>
> [  959.038043] amdgpu 0000:00:07.0:   in page starting at address 0x0000000000567000 from client 18
>
> [  959.039014] amdgpu 0000:00:07.0: [mmhub] page fault (src_id:0 ring:0 vmid:0 pasid:0, for process  pid 0 thread  pid 0)
>
> [  959.040202] amdgpu 0000:00:07.0:   in page starting at address 0x0000000000567000 from client 18
>
> [  959.041174] amdgpu 0000:00:07.0: [mmhub] page fault (src_id:0 ring:0 vmid:0 pasid:0, for process  pid 0 thread  pid 0)
>
> [  959.042353] amdgpu 0000:00:07.0:   in page starting at address 0x0000000000567000 from client 18
>
> [  959.043325] amdgpu 0000:00:07.0: [mmhub] page fault (src_id:0 ring:0 vmid:0 pasid:0, for process  pid 0 thread  pid 0)
>
> [  959.044508] amdgpu 0000:00:07.0:   in page starting at address 0x0000000000567000 from client 18
>
> [  959.045480] amdgpu 0000:00:07.0: [mmhub] page fault (src_id:0 ring:0 vmid:0 pasid:0, for process  pid 0 thread  pid 0)
>
> [  959.046659] amdgpu 0000:00:07.0:   in page starting at address 0x0000000000567000 from client 18
>
> [  959.047631] amdgpu 0000:00:07.0: [mmhub] page fault (src_id:0 ring:0 vmid:0 pasid:0, for process  pid 0 thread  pid 0)
>
> [  959.048815] amdgpu 0000:00:07.0:   in page starting at address 0x0000000000567000 from client 18
>
> [  959.049787] amdgpu 0000:00:07.0: [mmhub] page fault (src_id:0 ring:0 vmid:0 pasid:0, for process  pid 0 thread  pid 0)
>
> [  959.050973] amdgpu 0000:00:07.0:   in page starting at address 0x0000000000567000 from client 18
>
> [  959.051950] amdgpu 0000:00:07.0: [mmhub] page fault (src_id:0 ring:0 vmid:0 pasid:0, for process  pid 0 thread  pid 0)
>
> [  959.053123] amdgpu 0000:00:07.0:   in page starting at address 0x0000000000567000 from client 18
>
> [  967.208705] amdgpu 0000:00:07.0: [drm:amdgpu_ib_ring_tests [amdgpu]] *ERROR* IB test failed on vcn_enc0 (-110).
>
> [  967.209879] [drm:amdgpu_device_init [amdgpu]] *ERROR* ib ring test failed (-110).
>
>
>
> [ 1209.384668] INFO: task modprobe:23957 blocked for more than 120 seconds.
>
> [ 1209.385605]       Tainted: G           OE     5.4.0-58-generic #64~18.04.1-Ubuntu
>
> [ 1209.386451] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>
> [ 1209.387342] modprobe        D    0 23957   1221 0x80004006
>
> [ 1209.387344] Call Trace:
>
> [ 1209.387354]  __schedule+0x293/0x720
>
> [ 1209.387356]  schedule+0x33/0xa0
>
> [ 1209.387357]  schedule_timeout+0x1d3/0x320
>
> [ 1209.387359]  ? schedule+0x33/0xa0
>
> [ 1209.387360]  ? schedule_timeout+0x1d3/0x320
>
> [ 1209.387363]  dma_fence_default_wait+0x1b2/0x1e0
>
> [ 1209.387364]  ? dma_fence_release+0x130/0x130
>
> [ 1209.387366]  dma_fence_wait_timeout+0xfd/0x110
>
> [ 1209.387773]  amdgpu_fence_wait_empty+0x90/0xc0 [amdgpu]
>
> [ 1209.387839]  amdgpu_fence_driver_fini+0xd6/0x110 [amdgpu]
>> Regards,
>> Christian.
>>
>>>> Regards,
>>>> Christian.
>>>>
>>>>> Signed-off-by: Roy Sun <Roy.Sun@amd.com>
>>>>> ---
>>>>>     drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c | 48
>>>> ++++++++++++++++++++---
>>>>>     1 file changed, 43 insertions(+), 5 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
>>>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
>>>>> index 6b0aeee61b8b..738ea65077ea 100644
>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
>>>>> @@ -41,6 +41,8 @@
>>>>>     #include "amdgpu.h"
>>>>>     #include "amdgpu_trace.h"
>>>>>
>>>>> +#define AMDGPU_FENCE_TIMEOUT  msecs_to_jiffies(1000) #define
>>>>> +AMDGPU_FENCE_GFX_XGMI_TIMEOUT msecs_to_jiffies(2000)
>>>>>     /*
>>>>>      * Fences
>>>>>      * Fences mark an event in the GPUs pipeline and are used @@
>>>>> -104,6
>>>>> +106,38 @@ static void amdgpu_fence_write(struct amdgpu_ring *ring,
>>>>> +u32
>>>> seq)
>>>>>     *drv->cpu_addr = cpu_to_le32(seq);
>>>>>     }
>>>>>
>>>>> +/**
>>>>> + * amdgpu_fence_wait_timeout - get the fence wait timeout
>>>>> + *
>>>>> + * @ring: ring the fence is associated with
>>>>> + *
>>>>> + * Returns the value of the fence wait timeout.
>>>>> + */
>>>>> +long amdgpu_fence_wait_timeout(struct amdgpu_ring *ring) { long
>>>>> +tmo_gfx, tmo_mm, tmo; struct amdgpu_device *adev = ring->adev;
>>>>> +tmo_mm = tmo_gfx = AMDGPU_FENCE_TIMEOUT; if
>> (amdgpu_sriov_vf(adev))
>>>>> +{ tmo_mm = 8 * AMDGPU_FENCE_TIMEOUT; } if
>>>>> +(amdgpu_sriov_runtime(adev)) { tmo_gfx = 8 *
>> AMDGPU_FENCE_TIMEOUT;
>>>>> +} else if (adev->gmc.xgmi.hive_id) { tmo_gfx =
>>>>> +AMDGPU_FENCE_GFX_XGMI_TIMEOUT; } if (ring->funcs->type ==
>>>>> +AMDGPU_RING_TYPE_UVD ||
>>>>> +ring->funcs->type == AMDGPU_RING_TYPE_VCE || type ==
>>>>> +ring->funcs->AMDGPU_RING_TYPE_UVD_ENC || type ==
>>>>> +ring->funcs->AMDGPU_RING_TYPE_VCN_DEC || type ==
>>>>> +ring->funcs->AMDGPU_RING_TYPE_VCN_ENC || type ==
>>>>> +ring->funcs->AMDGPU_RING_TYPE_VCN_JPEG)
>>>>> +tmo = tmo_mm;
>>>>> +else
>>>>> +tmo = tmo_gfx;
>>>>> +return tmo;
>>>>> +}
>>>>> +
>>>>>     /**
>>>>>      * amdgpu_fence_read - read a fence value
>>>>>      *
>>>>> @@ -166,10 +200,12 @@ int amdgpu_fence_emit(struct amdgpu_ring
>>>>> *ring,
>>>> struct dma_fence **f,
>>>>>     rcu_read_unlock();
>>>>>
>>>>>     if (old) {
>>>>> -r = dma_fence_wait(old, false);
>>>>> +long timeout;
>>>>> +timeout = amdgpu_fence_wait_timeout(ring); r =
>>>>> +dma_fence_wait_timeout(old, false, timeout);
>>>>>     dma_fence_put(old);
>>>>>     if (r)
>>>>> -return r;
>>>>> +return r < 0 ? r : 0;
>>>>>     }
>>>>>     }
>>>>>
>>>>> @@ -343,10 +379,12 @@ int amdgpu_fence_wait_empty(struct
>>>> amdgpu_ring *ring)
>>>>>     return 0;
>>>>>     }
>>>>>     rcu_read_unlock();
>>>>> -
>>>>> -r = dma_fence_wait(fence, false);
>>>>> +
>>>>> +long timeout;
>>>>> +timeout = amdgpu_fence_wait_timeout(ring); r =
>>>>> +dma_fence_wait_timeout(fence, false, timeout);
>>>>>     dma_fence_put(fence);
>>>>> -return r;
>>>>> +return r < 0 ? r : 0;
>>>>>     }
>>>>>
>>>>>     /**
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