[Intel-gfx] [PATCH] drm/i915: Differentiate between aliasing-ppgtt and ggtt pinning

[Andi Shyti]

Hi Chris,

On Thu, Mar 26, 2020 at 02:27:27PM +0000, Chris Wilson wrote:
> Userptr causes lockdep to complain when we are using the aliasing-ppgtt
> (and ggtt, but for that it is rightfully so to complain about) in that
> when we revoke the userptr we take a mutex which we also use to revoke
> the mmaps. However, we only revoke mmaps for GGTT bindings and we never
> allow userptr to create a GGTT binding so the warning should be false
> and is simply caused by our conflation of the aliasing-ppgtt with the
> ggtt. So lets try treating the binding into the aliasing-ppgtt as a
> separate lockclass from the ggtt. The downside is that we are
> deliberately suppressing lockdep;s ability to warn us of cycles.
                                ^^^^
typo

> 
> Closes: https://gitlab.freedesktop.org/drm/intel/issues/478

I'm not a big fan of links in commit messages, I think they would
be forbidden by law, but I'm not being picky on that.

I don't know, thogh, why your S-o-b is missing.

> ---
>  drivers/gpu/drm/i915/i915_vma.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> index 191577a98390..9f4a31cd54ac 100644
> --- a/drivers/gpu/drm/i915/i915_vma.c
> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -914,7 +914,8 @@ int i915_vma_pin(struct i915_vma *vma, u64 size, u64 alignment, u64 flags)
>  		wakeref = intel_runtime_pm_get(&vma->vm->i915->runtime_pm);
>  
>  	/* No more allocations allowed once we hold vm->mutex */
> -	err = mutex_lock_interruptible(&vma->vm->mutex);
> +	err = mutex_lock_interruptible_nested(&vma->vm->mutex,
> +					      !(flags & PIN_GLOBAL));
>  	if (err)
>  		goto err_fence;
>  
> @@ -1320,7 +1321,7 @@ int i915_vma_unbind(struct i915_vma *vma)
>  	if (err)
>  		goto out_rpm;
>  
> -	err = mutex_lock_interruptible(&vm->mutex);
> +	err = mutex_lock_interruptible_nested(&vma->vm->mutex, !wakeref);

looks reasonable to me. Thanks!

Are you planning to push it? You have my review for this.

Andi