[Intel-gfx] [PATCH v4] drm/i915: Show vma allocator stack when in doubt

[Mika Kuoppala]

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

> At the moment, gem_exec_gttfill fails with a sporadic EBUSY due to us
> wanting to unbind a pinned batch. Let's dump who first bound that vma to
> see if that helps us identify who still unexpectedly has it pinned.
>
> v2: We cannot allocate inside the printer (as it may be on an fs-reclaim
> path), so hope for the best and build the string on the stack
> v3: stack depth of 16 routinely overflows a 512 character string, limit
> it to 12 to avoid unsightly truncation.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_vma.c | 39 +++++++++++++++++++++++++++++++--
>  1 file changed, 37 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> index e82aa804cdba..d0e606e9b27a 100644
> --- a/drivers/gpu/drm/i915/i915_vma.c
> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -21,7 +21,7 @@
>   * IN THE SOFTWARE.
>   *
>   */
> - 
> +

Extra spaces we don't carry around.

>  #include "i915_vma.h"
>  
>  #include "i915_drv.h"
> @@ -30,6 +30,39 @@
>  
>  #include <drm/drm_gem.h>
>  
> +#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM) && IS_ENABLED(CONFIG_DRM_DEBUG_MM)
> +
> +#include <linux/stackdepot.h>
> +
> +static void vma_print_allocator(struct i915_vma *vma, const char *reason)
> +{
> +	unsigned long entries[12];

Someone might complain that the array len needs a define.
But it clearly does not need it.

> +	struct stack_trace trace = {
> +		.entries = entries,
> +		.max_entries = ARRAY_SIZE(entries),
> +	};
> +	char buf[512];

Under the umbrella of those two debug defines,
this should be fine. Perhaps even conservative,
but if it gets the job done,

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

> +
> +	if (!vma->node.stack) {
> +		DRM_DEBUG_DRIVER("vma.node [%08llx + %08llx] %s: unknown owner\n",
> +				 vma->node.start, vma->node.size, reason);
> +		return;
> +	}
> +
> +	depot_fetch_stack(vma->node.stack, &trace);
> +	snprint_stack_trace(buf, sizeof(buf), &trace, 0);
> +	DRM_DEBUG_DRIVER("vma.node [%08llx + %08llx] %s: inserted at %s\n",
> +			 vma->node.start, vma->node.size, reason, buf);
> +}
> +
> +#else
> +
> +static void vma_print_allocator(struct i915_vma *vma, const char *reason)
> +{
> +}
> +
> +#endif
> +
>  static void
>  i915_vma_retire(struct i915_gem_active *active, struct i915_request *rq)
>  {
> @@ -875,8 +908,10 @@ int i915_vma_unbind(struct i915_vma *vma)
>  	}
>  	GEM_BUG_ON(i915_vma_is_active(vma));
>  
> -	if (i915_vma_is_pinned(vma))
> +	if (i915_vma_is_pinned(vma)) {
> +		vma_print_allocator(vma, "is pinned");
>  		return -EBUSY;
> +	}
>  
>  	if (!drm_mm_node_allocated(&vma->node))
>  		return 0;
> -- 
> 2.18.0