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

[Daniel Vetter]

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 at 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.

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
> > > > > 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch