drm/i915: Use explicit flag to mark unreachable intel_context

I need to keep the GEM context around a bit longer so adding an explicit
flag for syncing execbuf with closed/abandonded contexts.

v2:
 * Use already available context flags. (Chris)
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200319170707.8262-1-chris@chris-wilson.co.uk
(cherry picked from commit 207e4a71)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/i915/gem/i915_gem_context.c

@@ -574,7 +574,7 @@ static void engines_idle_release(struct i915_gem_context *ctx,
 		int err = 0;
 
 		/* serialises with execbuf */
-		RCU_INIT_POINTER(ce->gem_context, NULL);
+		set_bit(CONTEXT_CLOSED_BIT, &ce->flags);
 		if (!intel_context_pin_if_active(ce))
 			continue;
 

drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c

@@ -2316,7 +2316,7 @@ static void eb_request_add(struct i915_execbuffer *eb)
 	prev = __i915_request_commit(rq);
 
 	/* Check that the context wasn't destroyed before submission */
-	if (likely(rcu_access_pointer(eb->context->gem_context))) {
+	if (likely(!intel_context_is_closed(eb->context))) {
 		attr = eb->gem_context->sched;
 
 		/*

drivers/gpu/drm/i915/gt/intel_context.c

@@ -97,6 +97,8 @@ int __intel_context_do_pin(struct intel_context *ce)
 {
 	int err;
 
+	GEM_BUG_ON(intel_context_is_closed(ce));
+
 	if (unlikely(!test_bit(CONTEXT_ALLOC_BIT, &ce->flags))) {
 		err = intel_context_alloc_state(ce);
 		if (err)

drivers/gpu/drm/i915/gt/intel_context.h

@@ -173,6 +173,11 @@ static inline bool intel_context_is_barrier(const struct intel_context *ce)
 	return test_bit(CONTEXT_BARRIER_BIT, &ce->flags);
 }
 
+static inline bool intel_context_is_closed(const struct intel_context *ce)
+{
+	return test_bit(CONTEXT_CLOSED_BIT, &ce->flags);
+}
+
 static inline bool intel_context_use_semaphores(const struct intel_context *ce)
 {
 	return test_bit(CONTEXT_USE_SEMAPHORES, &ce->flags);

drivers/gpu/drm/i915/gt/intel_context_types.h

@@ -62,10 +62,11 @@ struct intel_context {
 #define CONTEXT_BARRIER_BIT		0
 #define CONTEXT_ALLOC_BIT		1
 #define CONTEXT_VALID_BIT		2
-#define CONTEXT_USE_SEMAPHORES		3
-#define CONTEXT_BANNED			4
-#define CONTEXT_FORCE_SINGLE_SUBMISSION	5
-#define CONTEXT_NOPREEMPT		6
+#define CONTEXT_CLOSED_BIT		3
+#define CONTEXT_USE_SEMAPHORES		4
+#define CONTEXT_BANNED			5
+#define CONTEXT_FORCE_SINGLE_SUBMISSION	6
+#define CONTEXT_NOPREEMPT		7
 
 	u32 *lrc_reg_state;
 	u64 lrc_desc;