Re: [PATCH 1/4] drm/amdgpu/vcn: fix race condition issue for vcn start

[James Zhu <jamesz@xxxxxxx>]

On 2020-03-03 1:44 p.m., Christian König wrote:
> Am 03.03.20 um 19:16 schrieb James Zhu:
> > Fix race condition issue when multiple vcn starts are called.
> >
> > Signed-off-by: James Zhu <James.Zhu@xxxxxxx>
> > ---
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.c | 4 ++++
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.h | 1 +
> >   2 files changed, 5 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.c 
> > b/drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.c
> > index f96464e..aa7663f 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.c
> > @@ -63,6 +63,7 @@ int amdgpu_vcn_sw_init(struct amdgpu_device *adev)
> >       int i, r;
> >         INIT_DELAYED_WORK(&adev->vcn.idle_work, 
> > amdgpu_vcn_idle_work_handler);
> > +    mutex_init(&adev->vcn.vcn_pg_lock);
> >         switch (adev->asic_type) {
> >       case CHIP_RAVEN:
> > @@ -210,6 +211,7 @@ int amdgpu_vcn_sw_fini(struct amdgpu_device *adev)
> >       }
> >         release_firmware(adev->vcn.fw);
> > +    mutex_destroy(&adev->vcn.vcn_pg_lock);
> >         return 0;
> >   }
> > @@ -321,6 +323,7 @@ void amdgpu_vcn_ring_begin_use(struct amdgpu_ring 
> > *ring)
> >       struct amdgpu_device *adev = ring->adev;
> >       bool set_clocks = !cancel_delayed_work_sync(&adev->vcn.idle_work);
> >   +    mutex_lock(&adev->vcn.vcn_pg_lock);
>
> That still won't work correctly here.
>
> The whole idea of the cancel_delayed_work_sync() and 
> schedule_delayed_work() dance is that you have exactly one user of 
> that. If you have multiple rings that whole thing won't work correctly.
>
> To fix this you need to call mutex_lock() before 
> cancel_delayed_work_sync() and schedule_delayed_work() before 
> mutex_unlock().

Big lock definitely works. I am trying to use as smaller lock as 
possible here. the share resource which needs protect here are power 
gate process and dpg mode switch process.

if we move mutex_unlock() before schedule_delayed_work(. I am wondering 
what are the other necessary resources which need protect.

Thanks!

James

> Regards,
> Christian.
>
> >       if (set_clocks) {
> >           amdgpu_gfx_off_ctrl(adev, false);
> >           amdgpu_device_ip_set_powergating_state(adev, 
> > AMD_IP_BLOCK_TYPE_VCN,
> > @@ -345,6 +348,7 @@ void amdgpu_vcn_ring_begin_use(struct amdgpu_ring 
> > *ring)
> >             adev->vcn.pause_dpg_mode(adev, ring->me, &new_state);
> >       }
> > +    mutex_unlock(&adev->vcn.vcn_pg_lock);
> >   }
> >     void amdgpu_vcn_ring_end_use(struct amdgpu_ring *ring)
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.h 
> > b/drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.h
> > index 6fe0573..2ae110d 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.h
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.h
> > @@ -200,6 +200,7 @@ struct amdgpu_vcn {
> >       struct drm_gpu_scheduler *vcn_dec_sched[AMDGPU_MAX_VCN_INSTANCES];
> >       uint32_t         num_vcn_enc_sched;
> >       uint32_t         num_vcn_dec_sched;
> > +    struct mutex         vcn_pg_lock;
> >         unsigned    harvest_config;
> >       int (*pause_dpg_mode)(struct amdgpu_device *adev,
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