drm/i915: Show vma allocator stack when in doubt

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@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180628132206.8329-1-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index e82aa80..d0e606e 100644 (file)
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -21,7 +21,7 @@
  * IN THE SOFTWARE.
  *
  */
- 
+
 #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];
+       struct stack_trace trace = {
+               .entries = entries,
+               .max_entries = ARRAY_SIZE(entries),
+       };
+       char buf[512];
+
+       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;