[Intel-gfx] [PATCH v2] drm/i915: Fix premature LRC unpin in GuC mode

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

In GuC mode LRC pinning lifetime depends exclusively on the
request liftime. Since that is terminated by the seqno update
that opens up a race condition between GPU finishing writing
out the context image and the driver unpinning the LRC.

To extend the LRC lifetime we will employ a similar approach
to what legacy ringbuffer submission does.

We will start tracking the last submitted context per engine
and keep it pinned until it is replaced by another one.

Note that the driver unload path is a bit fragile and could
benefit greatly from efforts to unify the legacy and exec
list submission code paths.

At the moment i915_gem_context_fini has special casing for the
two which are potentialy not needed, and also depends on
i915_gem_cleanup_ringbuffer running before itself.

v2:
 * Move pinning into engine->emit_request and actually fix
   the reference/unreference logic. (Chris Wilson)

 * ring->dev can be NULL on driver unload so use a different
   route towards it.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Issue: VIZ-4277
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Nick Hoath <nicholas.hoath at intel.com>
---
I cannot test this with GuC but it passes BAT with execlists
and some real world smoke tests.
---
 drivers/gpu/drm/i915/i915_gem_context.c | 4 +++-
 drivers/gpu/drm/i915/intel_lrc.c        | 9 ++++++++-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index c25083c78ba7..0b419e165836 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -438,7 +438,9 @@ void i915_gem_context_fini(struct drm_device *dev)
 	for (i = 0; i < I915_NUM_RINGS; i++) {
 		struct intel_engine_cs *ring = &dev_priv->ring[i];
 
-		if (ring->last_context)
+		if (ring->last_context && i915.enable_execlists)
+			intel_lr_context_unpin(ring->last_context, ring);
+		else if (ring->last_context)
 			i915_gem_context_unreference(ring->last_context);
 
 		ring->default_context = NULL;
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index e7c273acac1e..72ed176e091d 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1120,7 +1120,7 @@ void intel_lr_context_unpin(struct intel_context *ctx,
 {
 	struct drm_i915_gem_object *ctx_obj = ctx->engine[engine->id].state;
 
-	WARN_ON(!mutex_is_locked(&engine->dev->struct_mutex));
+	WARN_ON(!mutex_is_locked(&ctx->i915->dev->struct_mutex));
 
 	if (WARN_ON_ONCE(!ctx_obj))
 		return;
@@ -1859,6 +1859,13 @@ static int gen8_emit_request(struct drm_i915_gem_request *request)
 	u32 cmd;
 	int ret;
 
+	if (ring->last_context != request->ctx) {
+		if (ring->last_context)
+			intel_lr_context_unpin(ring->last_context, ring);
+		intel_lr_context_pin(request->ctx, ring);
+		ring->last_context = request->ctx;
+	}
+
 	/*
 	 * Reserve space for 2 NOOPs at the end of each request to be
 	 * used as a workaround for not being allowed to do lite
-- 
1.9.1