drm/i915/selftests: Exercise adding requests to a full GGTT

A bug recently encountered involved the issue where are we were
submitting requests to different ppGTT, each would pin a segment of the
GGTT for its logical context and ring. However, this is invisible to
eviction as we do not tie the context/ring VMA to a request and so do
not automatically wait upon it them (instead they are marked as pinned,
preventing eviction entirely). Instead the eviction code must flush those
contexts by switching to the kernel context. This selftest tries to
fill the GGTT with contexts to exercise a path where the
switch-to-kernel-context failed to make forward progress and we fail
with ENOSPC.

v2: Make the hole in the filled GGTT explicit.
v3: Swap out the arbitrary timeout for a private notification from
i915_gem_evict_something()

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171012125726.14736-3-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_evict.c b/drivers/gpu/drm/i915/i915_gem_evict.c
index ee4811ffb7aa..8daa8a78cdc0 100644
--- a/drivers/gpu/drm/i915/i915_gem_evict.c
+++ b/drivers/gpu/drm/i915/i915_gem_evict.c
@@ -33,6 +33,10 @@
 #include "intel_drv.h"
 #include "i915_trace.h"
 
+I915_SELFTEST_DECLARE(static struct igt_evict_ctl {
+	bool fail_if_busy:1;
+} igt_evict_ctl;)
+
 static bool ggtt_is_idle(struct drm_i915_private *i915)
 {
        struct intel_engine_cs *engine;
@@ -205,6 +209,9 @@ search_again:
 	 * the kernel's there is no more we can evict.
 	 */
 	if (!ggtt_is_idle(dev_priv)) {
+		if (I915_SELFTEST_ONLY(igt_evict_ctl.fail_if_busy))
+			return -EBUSY;
+
 		ret = ggtt_flush(dev_priv);
 		if (ret)
 			return ret;