[AMD Official Use Only - Internal Distribution Only]
Hi, Christian and Andrey,
We maybe try to implement "wait" callback function of dma_fence_ops, when GPU reset or unplug happen, make this callback return - ENODEV, to notify the caller device lost.
* Must return -ERESTARTSYS if the wait is intr = true and the wait was
* interrupted, and remaining jiffies if fence has signaled, or 0 if wait
* timed out. Can also return other error values on custom implementations,
* which should be treated as if the fence is signaled. For example a hardware
* lockup could be reported like that.
*
* This callback is optional.
*/
signed long (*wait)(struct dma_fence *fence,
bool intr, signed long timeout);
Best Regards
Dennis Li
-----Original Message-----
From: Christian König <ckoenig.leichtzumerken@xxxxxxxxx>
Sent: Tuesday, April 13, 2021 3:10 PM
To: Grodzovsky, Andrey <Andrey.Grodzovsky@xxxxxxx>; Koenig, Christian <Christian.Koenig@xxxxxxx>; Li, Dennis <Dennis.Li@xxxxxxx>; amd-gfx@xxxxxxxxxxxxxxxxxxxxx; Deucher, Alexander <Alexander.Deucher@xxxxxxx>; Kuehling, Felix <Felix.Kuehling@xxxxxxx>; Zhang, Hawking <Hawking.Zhang@xxxxxxx>; Daniel Vetter <daniel@xxxxxxxx>
Subject: Re: [PATCH 0/4] Refine GPU recovery sequence to enhance its stability
Am 12.04.21 um 22:01 schrieb Andrey Grodzovsky:
>
> On 2021-04-12 3:18 p.m., Christian König wrote:
>> Am 12.04.21 um 21:12 schrieb Andrey Grodzovsky:
>>> [SNIP]
>>>>>
>>>>> So what's the right approach ? How we guarantee that when running
>>>>> amdgpu_fence_driver_force_completion we will signal all the HW
>>>>> fences and not racing against some more fences insertion into that
>>>>> array ?
>>>>>
>>>>
>>>> Well I would still say the best approach would be to insert this
>>>> between the front end and the backend and not rely on signaling
>>>> fences while holding the device srcu.
>>>
>>>
>>> My question is, even now, when we run
>>> amdgpu_fence_driver_fini_hw->amdgpu_fence_wait_empty or
>>> amdgpu_fence_driver_fini_hw->amdgpu_fence_driver_force_completion,
>>> what there prevents a race with another fence being at the same time
>>> emitted and inserted into the fence array ? Looks like nothing.
>>>
>>
>> Each ring can only be used by one thread at the same time, this
>> includes emitting fences as well as other stuff.
>>
>> During GPU reset we make sure nobody writes to the rings by stopping
>> the scheduler and taking the GPU reset lock (so that nobody else can
>> start the scheduler again).
>
>
> What about direct submissions not through scheduler -
> amdgpu_job_submit_direct, I don't see how this is protected.
Those only happen during startup and GPU reset.
>>
>>>>
>>>> BTW: Could it be that the device SRCU protects more than one device
>>>> and we deadlock because of this?
>>>
>>>
>>> I haven't actually experienced any deadlock until now but, yes,
>>> drm_unplug_srcu is defined as static in drm_drv.c and so in the
>>> presence of multiple devices from same or different drivers we in
>>> fact are dependent on all their critical sections i guess.
>>>
>>
>> Shit, yeah the devil is a squirrel. So for A+I laptops we actually
>> need to sync that up with Daniel and the rest of the i915 guys.
>>
>> IIRC we could actually have an amdgpu device in a docking station
>> which needs hotplug and the driver might depend on waiting for the
>> i915 driver as well.
>
>
> Can't we propose a patch to make drm_unplug_srcu per drm_device ? I
> don't see why it has to be global and not per device thing.
I'm really wondering the same thing for quite a while now.
Adding Daniel as well, maybe he knows why the drm_unplug_srcu is global.
Regards,
Christian.
>
> Andrey
>
>
>>
>> Christian.
>>
>>> Andrey
>>>
>>>
>>>>
>>>> Christian.
>>>>
>>>>> Andrey
>>>>>
>>>>>
>>>>>>
>>>>>>> Andrey
>>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>> Christian.
>>>>>>>>
>>>>>>>>> /* Past this point no more fence are submitted to HW ring
>>>>>>>>> and hence we can safely call force signal on all that are
>>>>>>>>> currently there.
>>>>>>>>> * Any subsequently created HW fences will be returned
>>>>>>>>> signaled with an error code right away
>>>>>>>>> */
>>>>>>>>>
>>>>>>>>> for_each_ring(adev)
>>>>>>>>> amdgpu_fence_process(ring)
>>>>>>>>>
>>>>>>>>> drm_dev_unplug(dev);
>>>>>>>>> Stop schedulers
>>>>>>>>> cancel_sync(all timers and queued works);
>>>>>>>>> hw_fini
>>>>>>>>> unmap_mmio
>>>>>>>>>
>>>>>>>>> }
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Andrey
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Alternatively grabbing the reset write side and stopping
>>>>>>>>>>>>>> and then restarting the scheduler could work as well.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Christian.
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> I didn't get the above and I don't see why I need to reuse
>>>>>>>>>>>>> the GPU reset rw_lock. I rely on the SRCU unplug flag for
>>>>>>>>>>>>> unplug. Also, not clear to me why are we focusing on the
>>>>>>>>>>>>> scheduler threads, any code patch to generate HW fences
>>>>>>>>>>>>> should be covered, so any code leading to
>>>>>>>>>>>>> amdgpu_fence_emit needs to be taken into account such as,
>>>>>>>>>>>>> direct IB submissions, VM flushes e.t.c
>>>>>>>>>>>>
>>>>>>>>>>>> You need to work together with the reset lock anyway, cause
>>>>>>>>>>>> a hotplug could run at the same time as a reset.
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> For going my way indeed now I see now that I have to take
>>>>>>>>>>> reset write side lock during HW fences signalling in order
>>>>>>>>>>> to protect against scheduler/HW fences detachment and
>>>>>>>>>>> reattachment during schedulers stop/restart. But if we go
>>>>>>>>>>> with your approach then calling drm_dev_unplug and scoping
>>>>>>>>>>> amdgpu_job_timeout with drm_dev_enter/exit should be enough
>>>>>>>>>>> to prevent any concurrent GPU resets during unplug. In fact
>>>>>>>>>>> I already do it anyway -
>>>>>>>>>>> https://nam11.safelinks.protection.outlook.com/?url=https:%2
>>>>>>>>>>> F%2Fcgit.freedesktop.org%2F~agrodzov%2Flinux%2Fcommit%2F%3Fh
>>>>>>>>>>> %3Ddrm-misc-next%26id%3Def0ea4dd29ef44d2649c5eda16c8f4869acc
>>>>>>>>>>> 36b1&data=04%7C01%7CDennis.Li%40amd.com%7Cc7fc6cb505c34a
>>>>>>>>>>> edfe6d08d8fe4b3947%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C
>>>>>>>>>>> 0%7C637538946323194151%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wL
>>>>>>>>>>> jAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000
>>>>>>>>>>> &sdata=%2Fe%2BqJNlcuUjLHsLvfHCKqerK%2Ff8lzujqOBhnMBIRP8E
>>>>>>>>>>> %3D&reserved=0
>>>>>>>>>>
>>>>>>>>>> Yes, good point as well.
>>>>>>>>>>
>>>>>>>>>> Christian.
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Andrey
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> Christian.
>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> Andrey
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Christian.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> Andrey
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> Andrey
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>
>>>>>>
>>>>
>>
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