Re: [PATCH v2 8/8] drm/amdgpu: Prevent any job recoveries after device is unplugged.

[Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>]

On 11/17/20 2:49 PM, Daniel Vetter wrote:
> On Tue, Nov 17, 2020 at 02:18:49PM -0500, Andrey Grodzovsky wrote:
>> On 11/17/20 1:52 PM, Daniel Vetter wrote:
>>> On Tue, Nov 17, 2020 at 01:38:14PM -0500, Andrey Grodzovsky wrote:
>>>> On 6/22/20 5:53 AM, Daniel Vetter wrote:
>>>>> On Sun, Jun 21, 2020 at 02:03:08AM -0400, Andrey Grodzovsky wrote:
>>>>>> No point to try recovery if device is gone, just messes up things.
>>>>>>
>>>>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
>>>>>> ---
>>>>>>     drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c | 16 ++++++++++++++++
>>>>>>     drivers/gpu/drm/amd/amdgpu/amdgpu_job.c |  8 ++++++++
>>>>>>     2 files changed, 24 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
>>>>>> index 6932d75..5d6d3d9 100644
>>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
>>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
>>>>>> @@ -1129,12 +1129,28 @@ static int amdgpu_pci_probe(struct pci_dev *pdev,
>>>>>>     	return ret;
>>>>>>     }
>>>>>> +static void amdgpu_cancel_all_tdr(struct amdgpu_device *adev)
>>>>>> +{
>>>>>> +	int i;
>>>>>> +
>>>>>> +	for (i = 0; i < AMDGPU_MAX_RINGS; ++i) {
>>>>>> +		struct amdgpu_ring *ring = adev->rings[i];
>>>>>> +
>>>>>> +		if (!ring || !ring->sched.thread)
>>>>>> +			continue;
>>>>>> +
>>>>>> +		cancel_delayed_work_sync(&ring->sched.work_tdr);
>>>>>> +	}
>>>>>> +}
>>>>> I think this is a function that's supposed to be in drm/scheduler, not
>>>>> here. Might also just be your cleanup code being ordered wrongly, or your
>>>>> split in one of the earlier patches not done quite right.
>>>>> -Daniel
>>>> This function iterates across all the schedulers  per amdgpu device and accesses
>>>> amdgpu specific structures , drm/scheduler deals with single scheduler at most
>>>> so looks to me like this is the right place for this function
>>> I guess we could keep track of all schedulers somewhere in a list in
>>> struct drm_device and wrap this up. That was kinda the idea.
>>>
>>> Minimally I think a tiny wrapper with docs for the
>>> cancel_delayed_work_sync(&sched->work_tdr); which explains what you must
>>> observe to make sure there's no race.
>>
>> Will do
>>
>>
>>> I'm not exactly sure there's no
>>> guarantee here we won't get a new tdr work launched right afterwards at
>>> least, so this looks a bit like a hack.
>>
>> Note that for any TDR work happening post amdgpu_cancel_all_tdr
>> amdgpu_job_timedout->drm_dev_is_unplugged
>> will return true and so it will return early. To make it water proof tight
>> against race
>> i can switch from drm_dev_is_unplugged to drm_dev_enter/exit
> Hm that's confusing. You do a work_cancel_sync, so that at least looks
> like "tdr work must not run after this point"
>
> If you only rely on drm_dev_enter/exit check with the tdr work, then
> there's no need to cancel anything.


Agree, synchronize_srcu from drm_dev_unplug should play the role
of 'flushing' any earlier (in progress) tdr work which is
using drm_dev_enter/exit pair. Any later arising tdr will terminate early when 
drm_dev_enter
returns false.

Will update.

Andrey


>
> For race free cancel_work_sync you need:
> 1. make sure whatever is calling schedule_work is guaranteed to no longer
> call schedule_work.
> 2. call cancel_work_sync
>
> Anything else is cargo-culted work cleanup:
>
> - 1. without 2. means if a work got scheduled right before it'll still be
>    a problem.
> - 2. without 1. means a schedule_work right after makes you calling
>    cancel_work_sync pointless.
>
> So either both or nothing.
> -Daniel
>
>> Andrey
>>
>>
>>> -Daniel
>>>
>>>> Andrey
>>>>
>>>>
>>>>>> +
>>>>>>     static void
>>>>>>     amdgpu_pci_remove(struct pci_dev *pdev)
>>>>>>     {
>>>>>>     	struct drm_device *dev = pci_get_drvdata(pdev);
>>>>>> +	struct amdgpu_device *adev = dev->dev_private;
>>>>>>     	drm_dev_unplug(dev);
>>>>>> +	amdgpu_cancel_all_tdr(adev);
>>>>>>     	ttm_bo_unmap_virtual_address_space(&adev->mman.bdev);
>>>>>>     	amdgpu_driver_unload_kms(dev);
>>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
>>>>>> index 4720718..87ff0c0 100644
>>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
>>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
>>>>>> @@ -28,6 +28,8 @@
>>>>>>     #include "amdgpu.h"
>>>>>>     #include "amdgpu_trace.h"
>>>>>> +#include <drm/drm_drv.h>
>>>>>> +
>>>>>>     static void amdgpu_job_timedout(struct drm_sched_job *s_job)
>>>>>>     {
>>>>>>     	struct amdgpu_ring *ring = to_amdgpu_ring(s_job->sched);
>>>>>> @@ -37,6 +39,12 @@ static void amdgpu_job_timedout(struct drm_sched_job *s_job)
>>>>>>     	memset(&ti, 0, sizeof(struct amdgpu_task_info));
>>>>>> +	if (drm_dev_is_unplugged(adev->ddev)) {
>>>>>> +		DRM_INFO("ring %s timeout, but device unplugged, skipping.\n",
>>>>>> +					  s_job->sched->name);
>>>>>> +		return;
>>>>>> +	}
>>>>>> +
>>>>>>     	if (amdgpu_ring_soft_recovery(ring, job->vmid, s_job->s_fence->parent)) {
>>>>>>     		DRM_ERROR("ring %s timeout, but soft recovered\n",
>>>>>>     			  s_job->sched->name);
>>>>>> -- 
>>>>>> 2.7.4
>>>>>>
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