[PATCH] drm/amdgpu: workaround for TLB seq race

[Alex Deucher]

On Wed, Nov 2, 2022 at 10:58 AM Christian König
<ckoenig.leichtzumerken at gmail.com> wrote:
>
> It can happen that we query the sequence value before the callback
> had a chance to run.
>
> Work around that by grabbing the fence lock and releasing it again.

workaround

> Should be replaced by hw handling soon.
>
> Signed-off-by: Christian König <christian.koenig at amd.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> index 9ecb7f663e19..e51a46c9582b 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> @@ -485,6 +485,21 @@ void amdgpu_debugfs_vm_bo_info(struct amdgpu_vm *vm, struct seq_file *m);
>   */
>  static inline uint64_t amdgpu_vm_tlb_seq(struct amdgpu_vm *vm)
>  {
> +       unsigned long flags;
> +       spinlock_t *lock;
> +
> +       /*
> +        * Work around to stop racing between the fence signaling and handling

Workaround

WIth that fixed up, the patch is:
Acked-by: Alex Deucher <alexander.deucher at amd.com>


> +        * the cb. The lock is static after initially setting it up, just make
> +        * sure that the dma_fence structure isn't freed up.
> +        */
> +       rcu_read_lock();
> +       lock = vm->last_tlb_flush->lock;
> +       rcu_read_unlock();
> +
> +       spin_lock_irqsave(lock, flags);
> +       spin_unlock_irqrestore(lock, flags);
> +
>         return atomic64_read(&vm->tlb_seq);
>  }
>
> --
> 2.34.1
>