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

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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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