Re: [Intel-gfx] [PATCH] drm/i915/gem: Split eb_vma into its own allocation

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> Use a separate array allocation for the execbuf vma, so that we can
> track their lifetime independently from the copy of the user arguments.
> With luck, this has a secondary benefit of splitting the malloc size to
> within reason and avoid vmalloc. The downside is that we might require
> two separate vmallocs -- but much less likely.
>
> In the process, this prevents a memory leak on the ww_mutex error
> unwind.
>
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/1390
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>

> ---
>  .../gpu/drm/i915/gem/i915_gem_execbuffer.c    | 131 ++++++++++--------
>  1 file changed, 73 insertions(+), 58 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> index f347e595a773..cda35e6dfc44 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> @@ -40,6 +40,11 @@ struct eb_vma {
>  	u32 handle;
>  };
>  
> +struct eb_vma_array {
> +	struct kref kref;
> +	struct eb_vma vma[];
> +};
> +
>  enum {
>  	FORCE_CPU_RELOC = 1,
>  	FORCE_GTT_RELOC,
> @@ -52,7 +57,6 @@ enum {
>  #define __EXEC_OBJECT_NEEDS_MAP		BIT(29)
>  #define __EXEC_OBJECT_NEEDS_BIAS	BIT(28)
>  #define __EXEC_OBJECT_INTERNAL_FLAGS	(~0u << 28) /* all of the above */
> -#define __EXEC_OBJECT_RESERVED (__EXEC_OBJECT_HAS_PIN | __EXEC_OBJECT_HAS_FENCE)
>  
>  #define __EXEC_HAS_RELOC	BIT(31)
>  #define __EXEC_INTERNAL_FLAGS	(~0u << 31)
> @@ -283,6 +287,7 @@ struct i915_execbuffer {
>  	 */
>  	int lut_size;
>  	struct hlist_head *buckets; /** ht for relocation handles */
> +	struct eb_vma_array *array;
>  };
>  
>  static inline bool eb_use_cmdparser(const struct i915_execbuffer *eb)
> @@ -292,8 +297,62 @@ static inline bool eb_use_cmdparser(const struct i915_execbuffer *eb)
>  		 eb->args->batch_len);
>  }
>  
> +static struct eb_vma_array *eb_vma_array_create(unsigned int count)
> +{
> +	struct eb_vma_array *arr;
> +
> +	arr = kvmalloc(struct_size(arr, vma, count), GFP_KERNEL | __GFP_NOWARN);
> +	if (!arr)
> +		return NULL;
> +
> +	kref_init(&arr->kref);
> +	arr->vma[0].vma = NULL;
> +
> +	return arr;
> +}
> +
> +static inline void eb_unreserve_vma(struct eb_vma *ev)
> +{
> +	struct i915_vma *vma = ev->vma;
> +
> +	if (unlikely(ev->flags & __EXEC_OBJECT_HAS_FENCE))
> +		__i915_vma_unpin_fence(vma);
> +
> +	if (ev->flags & __EXEC_OBJECT_HAS_PIN)
> +		__i915_vma_unpin(vma);
> +
> +	ev->flags &= ~(__EXEC_OBJECT_HAS_PIN |
> +		       __EXEC_OBJECT_HAS_FENCE);
> +}
> +
> +static void eb_vma_array_destroy(struct kref *kref)
> +{
> +	struct eb_vma_array *arr = container_of(kref, typeof(*arr), kref);
> +	struct eb_vma *ev = arr->vma;
> +
> +	while (ev->vma) {
> +		eb_unreserve_vma(ev);
> +		i915_vma_put(ev->vma);
> +		ev++;
> +	}
> +
> +	kvfree(arr);
> +}
> +
> +static void eb_vma_array_put(struct eb_vma_array *arr)
> +{
> +	kref_put(&arr->kref, eb_vma_array_destroy);
> +}
> +
>  static int eb_create(struct i915_execbuffer *eb)
>  {
> +	/* Allocate an extra slot for use by the command parser + sentinel */
> +	eb->array = eb_vma_array_create(eb->buffer_count + 2);
> +	if (!eb->array)
> +		return -ENOMEM;
> +
> +	eb->vma = eb->array->vma;
> +
>  	if (!(eb->args->flags & I915_EXEC_HANDLE_LUT)) {
>  		unsigned int size = 1 + ilog2(eb->buffer_count);
>  
> @@ -327,8 +386,10 @@ static int eb_create(struct i915_execbuffer *eb)
>  				break;
>  		} while (--size);
>  
> -		if (unlikely(!size))
> +		if (unlikely(!size)) {
> +			eb_vma_array_put(eb->array);
>  			return -ENOMEM;
> +		}
>  
>  		eb->lut_size = size;
>  	} else {
> @@ -402,26 +463,6 @@ eb_pin_vma(struct i915_execbuffer *eb,
>  	return !eb_vma_misplaced(entry, vma, ev->flags);
>  }
>  
> -static inline void __eb_unreserve_vma(struct i915_vma *vma, unsigned int flags)
> -{
> -	GEM_BUG_ON(!(flags & __EXEC_OBJECT_HAS_PIN));
> -
> -	if (unlikely(flags & __EXEC_OBJECT_HAS_FENCE))
> -		__i915_vma_unpin_fence(vma);
> -
> -	__i915_vma_unpin(vma);
> -}
> -
> -static inline void
> -eb_unreserve_vma(struct eb_vma *ev)
> -{
> -	if (!(ev->flags & __EXEC_OBJECT_HAS_PIN))
> -		return;
> -
> -	__eb_unreserve_vma(ev->vma, ev->flags);
> -	ev->flags &= ~__EXEC_OBJECT_RESERVED;
> -}
> -
>  static int
>  eb_validate_vma(struct i915_execbuffer *eb,
>  		struct drm_i915_gem_exec_object2 *entry,
> @@ -863,31 +904,13 @@ eb_get_vma(const struct i915_execbuffer *eb, unsigned long handle)
>  	}
>  }
>  
> -static void eb_release_vmas(const struct i915_execbuffer *eb)
> -{
> -	const unsigned int count = eb->buffer_count;
> -	unsigned int i;
> -
> -	for (i = 0; i < count; i++) {
> -		struct eb_vma *ev = &eb->vma[i];
> -		struct i915_vma *vma = ev->vma;
> -
> -		if (!vma)
> -			break;
> -
> -		eb->vma[i].vma = NULL;
> -
> -		if (ev->flags & __EXEC_OBJECT_HAS_PIN)
> -			__eb_unreserve_vma(vma, ev->flags);
> -
> -		i915_vma_put(vma);
> -	}
> -}
> -
>  static void eb_destroy(const struct i915_execbuffer *eb)
>  {
>  	GEM_BUG_ON(eb->reloc_cache.rq);
>  
> +	if (eb->array)
> +		eb_vma_array_put(eb->array);
> +
>  	if (eb->lut_size > 0)
>  		kfree(eb->buckets);
>  }
> @@ -1635,19 +1658,15 @@ static int eb_move_to_gpu(struct i915_execbuffer *eb)
>  			err = i915_vma_move_to_active(vma, eb->request, flags);
>  
>  		i915_vma_unlock(vma);
> -
> -		__eb_unreserve_vma(vma, flags);
> -		i915_vma_put(vma);
> -
> -		ev->vma = NULL;
> +		eb_unreserve_vma(ev);
>  	}
>  	ww_acquire_fini(&acquire);
>  
> +	eb_vma_array_put(fetch_and_zero(&eb->array));
> +
>  	if (unlikely(err))
>  		goto err_skip;
>  
> -	eb->exec = NULL;
> -
>  	/* Unconditionally flush any chipset caches (for streaming writes). */
>  	intel_gt_chipset_flush(eb->engine->gt);
>  	return 0;
> @@ -1899,6 +1918,7 @@ static int eb_parse(struct i915_execbuffer *eb)
>  	eb->vma[eb->buffer_count].vma = i915_vma_get(shadow);
>  	eb->vma[eb->buffer_count].flags = __EXEC_OBJECT_HAS_PIN;
>  	eb->batch = &eb->vma[eb->buffer_count++];
> +	eb->vma[eb->buffer_count].vma = NULL;
>  
>  	eb->trampoline = trampoline;
>  	eb->batch_start_offset = 0;
> @@ -2422,8 +2442,6 @@ i915_gem_do_execbuffer(struct drm_device *dev,
>  		args->flags |= __EXEC_HAS_RELOC;
>  
>  	eb.exec = exec;
> -	eb.vma = (struct eb_vma *)(exec + args->buffer_count + 1);
> -	eb.vma[0].vma = NULL;
>  
>  	eb.invalid_flags = __EXEC_OBJECT_UNKNOWN_FLAGS;
>  	reloc_cache_init(&eb.reloc_cache, eb.i915);
> @@ -2630,8 +2648,6 @@ i915_gem_do_execbuffer(struct drm_device *dev,
>  	if (batch->private)
>  		intel_engine_pool_put(batch->private);
>  err_vma:
> -	if (eb.exec)
> -		eb_release_vmas(&eb);
>  	if (eb.trampoline)
>  		i915_vma_unpin(eb.trampoline);
>  	eb_unpin_engine(&eb);
> @@ -2651,7 +2667,7 @@ i915_gem_do_execbuffer(struct drm_device *dev,
>  
>  static size_t eb_element_size(void)
>  {
> -	return sizeof(struct drm_i915_gem_exec_object2) + sizeof(struct eb_vma);
> +	return sizeof(struct drm_i915_gem_exec_object2);
>  }
>  
>  static bool check_buffer_count(size_t count)
> @@ -2707,7 +2723,7 @@ i915_gem_execbuffer_ioctl(struct drm_device *dev, void *data,
>  	/* Copy in the exec list from userland */
>  	exec_list = kvmalloc_array(count, sizeof(*exec_list),
>  				   __GFP_NOWARN | GFP_KERNEL);
> -	exec2_list = kvmalloc_array(count + 1, eb_element_size(),
> +	exec2_list = kvmalloc_array(count, eb_element_size(),
>  				    __GFP_NOWARN | GFP_KERNEL);
>  	if (exec_list == NULL || exec2_list == NULL) {
>  		drm_dbg(&i915->drm,
> @@ -2785,8 +2801,7 @@ i915_gem_execbuffer2_ioctl(struct drm_device *dev, void *data,
>  	if (err)
>  		return err;
>  
> -	/* Allocate an extra slot for use by the command parser */
> -	exec2_list = kvmalloc_array(count + 1, eb_element_size(),
> +	exec2_list = kvmalloc_array(count, eb_element_size(),
>  				    __GFP_NOWARN | GFP_KERNEL);
>  	if (exec2_list == NULL) {
>  		drm_dbg(&i915->drm, "Failed to allocate exec list for %zd buffers\n",
> -- 
> 2.20.1
>
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