drm/i915: Handle idling during i915_gem_evict_something busy loops

i915_gem_evict_something() is charged with finding a slot within the GTT
that we may reuse. Since our goal is not to stall, we first look for a
slot that only overlaps idle vma. To this end, on the first pass we move
any active vma to the end of the search list. However, we only stopped
moving active vma after we see the first active vma twice. If during the
search, that first active vma completed, we would not notice and keep on
extending the search list.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/1746
Fixes: 2850748ef876 ("drm/i915: Pull i915_vma_pin under the vm->mutex")
Fixes: b1e3177bd1d8 ("drm/i915: Coordinate i915_active with its own mutex")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: <stable@vger.kernel.org> # v5.5+
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200509115217.26853-1-chris@chris-wilson.co.uk
(cherry picked from commit 73e28cc40bf00b5d168cb8f5cff1ae63e9097446)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

diff --git a/drivers/gpu/drm/i915/i915_gem_evict.c b/drivers/gpu/drm/i915/i915_gem_evict.c
index 4518b9b..02ad1ac 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem_evict.c
+++ b/drivers/gpu/drm/i915/i915_gem_evict.c
@@ -128,6 +128,13 @@ search_again:
        active = NULL;
        INIT_LIST_HEAD(&eviction_list);
        list_for_each_entry_safe(vma, next, &vm->bound_list, vm_link) {
+               if (vma == active) { /* now seen this vma twice */
+                       if (flags & PIN_NONBLOCK)
+                               break;
+
+                       active = ERR_PTR(-EAGAIN);
+               }
+
                /*
                 * We keep this list in a rough least-recently scanned order
                 * of active elements (inactive elements are cheap to reap).
@@ -143,21 +150,12 @@ search_again:
                 * To notice when we complete one full cycle, we record the
                 * first active element seen, before moving it to the tail.
                 */
-               if (i915_vma_is_active(vma)) {
-                       if (vma == active) {
-                               if (flags & PIN_NONBLOCK)
-                                       break;
-
-                               active = ERR_PTR(-EAGAIN);
-                       }
-
-                       if (active != ERR_PTR(-EAGAIN)) {
-                               if (!active)
-                                       active = vma;
+               if (active != ERR_PTR(-EAGAIN) && i915_vma_is_active(vma)) {
+                       if (!active)
+                               active = vma;
 
-                               list_move_tail(&vma->vm_link, &vm->bound_list);
-                               continue;
-                       }
+                       list_move_tail(&vma->vm_link, &vm->bound_list);
+                       continue;
                }
 
                if (mark_free(&scan, vma, flags, &eviction_list))