[Intel-gfx] [PATCH] drm/i915: Allow dead vm to unbind vma's without lock.

[Thomas Hellström (Intel)]

On 1/28/22 09:57, Maarten Lankhorst wrote:
> i915_gem_vm_close may take the lock, and we currently have no better way
> of handling this. At least for now, allow a path in which holding vm->mutex
> is sufficient. This is the case, because the object destroy path will
> forcefully take vm->mutex now.
>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>

Reviewed-by: Thomas Hellstrom <thomas.hellstrom at linux.intel.com>


> ---
>   drivers/gpu/drm/i915/i915_vma.c | 15 +++++++++++++--
>   1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> index b959e904c4d3..14a301c4069f 100644
> --- a/drivers/gpu/drm/i915/i915_vma.c
> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -40,6 +40,17 @@
>   #include "i915_vma.h"
>   #include "i915_vma_resource.h"
>   
> +static inline void assert_vma_held_evict(const struct i915_vma *vma)
> +{
> +	/*
> +	 * We may be forced to unbind when the vm is dead, to clean it up.
> +	 * This is the only exception to the requirement of the object lock
> +	 * being held.
> +	 */
> +	if (atomic_read(&vma->vm->open))
> +		assert_object_held_shared(vma->obj);
> +}
> +
>   static struct kmem_cache *slab_vmas;
>   
>   static struct i915_vma *i915_vma_alloc(void)
> @@ -1779,7 +1790,7 @@ struct dma_fence *__i915_vma_evict(struct i915_vma *vma, bool async)
>   	struct dma_fence *unbind_fence;
>   
>   	GEM_BUG_ON(i915_vma_is_pinned(vma));
> -	assert_object_held_shared(vma->obj);
> +	assert_vma_held_evict(vma);
>   
>   	if (i915_vma_is_map_and_fenceable(vma)) {
>   		/* Force a pagefault for domain tracking on next user access */
> @@ -1846,7 +1857,7 @@ int __i915_vma_unbind(struct i915_vma *vma)
>   	int ret;
>   
>   	lockdep_assert_held(&vma->vm->mutex);
> -	assert_object_held_shared(vma->obj);
> +	assert_vma_held_evict(vma);
>   
>   	if (!drm_mm_node_allocated(&vma->node))
>   		return 0;