[PATCH v4 13/17] drm/i915/vm_bind: Update i915_vma_verify_bind_complete()

[Niranjana Vishwanathapura]

On Thu, Oct 20, 2022 at 10:16:06AM +0100, Matthew Auld wrote:
>On 19/10/2022 19:28, Niranjana Vishwanathapura wrote:
>>On Wed, Oct 19, 2022 at 05:07:31PM +0100, Matthew Auld wrote:
>>>On 18/10/2022 08:16, Niranjana Vishwanathapura wrote:
>>>>Ensure i915_vma_verify_bind_complete() handles case where bind
>>>>is not initiated. Also make it non static, add documentation
>>>>and move it out of CONFIG_DRM_I915_DEBUG_GEM.
>>>>
>>>>Signed-off-by: Niranjana Vishwanathapura 
>>>><niranjana.vishwanathapura at intel.com>
>>>>Signed-off-by: Andi Shyti <andi.shyti at linux.intel.com>
>>>>---
>>>> drivers/gpu/drm/i915/i915_vma.c | 16 +++++++++++-----
>>>> drivers/gpu/drm/i915/i915_vma.h |  1 +
>>>> 2 files changed, 12 insertions(+), 5 deletions(-)
>>>>
>>>>diff --git a/drivers/gpu/drm/i915/i915_vma.c 
>>>>b/drivers/gpu/drm/i915/i915_vma.c
>>>>index eaa13e9ba966..4975fc662c86 100644
>>>>--- a/drivers/gpu/drm/i915/i915_vma.c
>>>>+++ b/drivers/gpu/drm/i915/i915_vma.c
>>>>@@ -439,12 +439,21 @@ int i915_vma_sync(struct i915_vma *vma)
>>>>     return i915_vm_sync(vma->vm);
>>>> }
>>>>-#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
>>>>-static int i915_vma_verify_bind_complete(struct i915_vma *vma)
>>>>+/**
>>>>+ * i915_vma_verify_bind_complete() - Check for the bind 
>>>>completion of the vma
>>>>+ * @vma: vma to check for bind completion
>>>
>>>Maybe mention the locking since this is now more than just 
>>>DEBUG_GEM stuff. I assume we need the object lock or otherwise 
>>>some guarantee that the vma is pinned?
>>>
>>>Reviewed-by: Matthew Auld <matthew.auld at intel.com>
>>>
>>
>>I think they are not needed. The fence reference is obtained under rcu
>>lock anyhow (will add this to documentation). Only thing required is
>>that vma is not released, but that caller must ensure for all i915_vma
>>apis anyhow.
>
>I was thinking more about how this potentially behaves with concurrent 
>bind/unbind, and what it might return in such cases. I'm assuming most 
>normal users will want to have an active pin and/or be holding the 
>object lock when calling this.
>

Unbind will anyway wait behind this fence. As it is just returning the
exclusive fence status, I think it should be fine even for concurrent
cases. Any specific sequence you are concerned with?
For vm_bind use case, we do have the object lock while calling it, but
I am not certain about the i915_vma_pin_iomap() use case. The permerge
CI result is clean though.

>>
>>Thanks,
>>Niranjana
>>
>>>>+ *
>>>>+ * Returns: 0 if the vma bind is completed. Error code otherwise.
>>>>+ */
>>>>+int i915_vma_verify_bind_complete(struct i915_vma *vma)
>>>> {
>>>>     struct dma_fence *fence = i915_active_fence_get(&vma->active.excl);
>>>>     int err;
>>>>+    /* Ensure vma bind is initiated */
>>>>+    if (!i915_vma_is_bound(vma, I915_VMA_BIND_MASK))
>
>Just realised that this leaks the fence. I guess we have yet to hit 
>this in testing.

Ah...will move i915_active_fence_get() below.

Thanks,
Niranjana

>
>>>>+        return -EINVAL;
>>>>+
>>>>     if (!fence)
>>>>         return 0;
>>>>@@ -457,9 +466,6 @@ static int 
>>>>i915_vma_verify_bind_complete(struct i915_vma *vma)
>>>>     return err;
>>>> }
>>>>-#else
>>>>-#define i915_vma_verify_bind_complete(_vma) 0
>>>>-#endif
>>>> I915_SELFTEST_EXPORT void
>>>> i915_vma_resource_init_from_vma(struct i915_vma_resource *vma_res,
>>>>diff --git a/drivers/gpu/drm/i915/i915_vma.h 
>>>>b/drivers/gpu/drm/i915/i915_vma.h
>>>>index 1cadbf8fdedf..04770f8ba815 100644
>>>>--- a/drivers/gpu/drm/i915/i915_vma.h
>>>>+++ b/drivers/gpu/drm/i915/i915_vma.h
>>>>@@ -440,6 +440,7 @@ void i915_vma_make_purgeable(struct i915_vma *vma);
>>>> int i915_vma_wait_for_bind(struct i915_vma *vma);
>>>> int i915_vma_sync(struct i915_vma *vma);
>>>>+int i915_vma_verify_bind_complete(struct i915_vma *vma);
>>>> /**
>>>>  * i915_vma_get_current_resource - Get the current resource of the vma