[PATCH 19/19] drm/i915: Remove GPU reset dependence on struct_mutex

Chris Wilson chris at chris-wilson.co.uk
Thu Jul 5 09:48:23 UTC 2018


Now that the submission backends are controlled via their own spinlocks,
with a wave of a magic wand we can lift the struct_mutex requirement
around GPU reset. That is we allow the submission frontend (userspace)
to keep on submitting while we process the GPU reset as we can suspend
the backend independently.

The major change is around the backoff/handoff strategy for performing
the reset. With no mutex deadlock, we no longer have to coordinate with
any waiter, and just perform the reset immediately.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_debugfs.c           |   7 -
 drivers/gpu/drm/i915/i915_drv.h               |   5 -
 drivers/gpu/drm/i915/i915_gem.c               |  18 +-
 drivers/gpu/drm/i915/i915_gem_fence_reg.c     |  39 ++-
 drivers/gpu/drm/i915/i915_gem_fence_reg.h     |   6 +-
 drivers/gpu/drm/i915/i915_gpu_error.h         |  22 +-
 drivers/gpu/drm/i915/i915_request.c           |  46 ---
 drivers/gpu/drm/i915/i915_reset.c             | 315 +++++++-----------
 drivers/gpu/drm/i915/i915_reset.h             |   3 +
 drivers/gpu/drm/i915/intel_engine_cs.c        |   6 +-
 drivers/gpu/drm/i915/intel_guc_submission.c   |   5 +-
 drivers/gpu/drm/i915/intel_lrc.c              |  98 ++----
 drivers/gpu/drm/i915/intel_overlay.c          |   2 -
 drivers/gpu/drm/i915/intel_ringbuffer.c       |  89 +++--
 drivers/gpu/drm/i915/intel_ringbuffer.h       |  13 +-
 .../gpu/drm/i915/selftests/intel_hangcheck.c  |  29 +-
 16 files changed, 270 insertions(+), 433 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index b2b8a12a85b8..978b5c845f93 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -1318,8 +1318,6 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
 		seq_puts(m, "Wedged\n");
 	if (test_bit(I915_RESET_BACKOFF, &dev_priv->gpu_error.flags))
 		seq_puts(m, "Reset in progress: struct_mutex backoff\n");
-	if (test_bit(I915_RESET_HANDOFF, &dev_priv->gpu_error.flags))
-		seq_puts(m, "Reset in progress: reset handoff to waiter\n");
 	if (waitqueue_active(&dev_priv->gpu_error.wait_queue))
 		seq_puts(m, "Waiter holding struct mutex\n");
 	if (waitqueue_active(&dev_priv->gpu_error.reset_queue))
@@ -4081,11 +4079,6 @@ i915_wedged_set(void *data, u64 val)
 
 	i915_handle_error(i915, val, I915_ERROR_CAPTURE,
 			  "Manually set wedged engine mask = %llx", val);
-
-	wait_on_bit(&i915->gpu_error.flags,
-		    I915_RESET_HANDOFF,
-		    TASK_UNINTERRUPTIBLE);
-
 	return 0;
 }
 
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index b3729e52c9d0..f65fa4c850b3 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3089,11 +3089,6 @@ static inline bool i915_reset_backoff(struct i915_gpu_error *error)
 	return unlikely(test_bit(I915_RESET_BACKOFF, &error->flags));
 }
 
-static inline bool i915_reset_handoff(struct i915_gpu_error *error)
-{
-	return unlikely(test_bit(I915_RESET_HANDOFF, &error->flags));
-}
-
 static inline bool i915_terminally_wedged(struct i915_gpu_error *error)
 {
 	return unlikely(test_bit(I915_WEDGED, &error->flags));
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index bef9c5e133a7..b1d8881a0860 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -655,11 +655,6 @@ i915_gem_object_wait(struct drm_i915_gem_object *obj,
 		     struct intel_rps_client *rps_client)
 {
 	might_sleep();
-#if IS_ENABLED(CONFIG_LOCKDEP)
-	GEM_BUG_ON(debug_locks &&
-		   !!lockdep_is_held(&obj->base.dev->struct_mutex) !=
-		   !!(flags & I915_WAIT_LOCKED));
-#endif
 	GEM_BUG_ON(timeout < 0);
 
 	timeout = i915_gem_object_wait_reservation(obj->resv,
@@ -4543,8 +4538,6 @@ void i915_gem_sanitize(struct drm_i915_private *i915)
 
 	GEM_TRACE("\n");
 
-	mutex_lock(&i915->drm.struct_mutex);
-
 	intel_runtime_pm_get(i915);
 	intel_uncore_forcewake_get(i915, FORCEWAKE_ALL);
 
@@ -4574,6 +4567,7 @@ void i915_gem_sanitize(struct drm_i915_private *i915)
 	intel_uncore_forcewake_put(i915, FORCEWAKE_ALL);
 	intel_runtime_pm_put(i915);
 
+	mutex_lock(&i915->drm.struct_mutex);
 	i915_gem_contexts_lost(i915);
 	mutex_unlock(&i915->drm.struct_mutex);
 }
@@ -4587,6 +4581,8 @@ int i915_gem_suspend(struct drm_i915_private *i915)
 	intel_runtime_pm_get(i915);
 	intel_suspend_gt_powersave(i915);
 
+	flush_workqueue(i915->wq);
+
 	mutex_lock(&i915->drm.struct_mutex);
 
 	/*
@@ -4613,11 +4609,9 @@ int i915_gem_suspend(struct drm_i915_private *i915)
 		assert_kernel_context_is_current(i915);
 	}
 	mutex_unlock(&i915->drm.struct_mutex);
+	i915_reset_flush(i915);
 
-	intel_uc_suspend(i915);
-
-	cancel_delayed_work_sync(&i915->gpu_error.hangcheck_work);
-	cancel_delayed_work_sync(&i915->gt.retire_work);
+	drain_delayed_work(&i915->gt.retire_work);
 
 	/*
 	 * As the idle_work is rearming if it detects a race, play safe and
@@ -4625,6 +4619,8 @@ int i915_gem_suspend(struct drm_i915_private *i915)
 	 */
 	drain_delayed_work(&i915->gt.idle_work);
 
+	intel_uc_suspend(i915);
+
 	/*
 	 * Assert that we successfully flushed all the work and
 	 * reset the GPU back to its idle, low power state.
diff --git a/drivers/gpu/drm/i915/i915_gem_fence_reg.c b/drivers/gpu/drm/i915/i915_gem_fence_reg.c
index 9313a8e675c8..e458ae189f82 100644
--- a/drivers/gpu/drm/i915/i915_gem_fence_reg.c
+++ b/drivers/gpu/drm/i915/i915_gem_fence_reg.c
@@ -473,7 +473,7 @@ void i915_unreserve_fence(struct drm_i915_fence_reg *fence)
 }
 
 /**
- * i915_gem_revoke_fences - revoke fence state
+ * __i915_gem_revoke_fences - revoke fence state
  * @i915: i915 device private
  *
  * Removes all GTT mmappings via the fence registers. This forces any user
@@ -482,12 +482,13 @@ void i915_unreserve_fence(struct drm_i915_fence_reg *fence)
  * revoke concurrent userspace access via GTT mmaps until the hardware has been
  * reset and the fence registers have been restored.
  */
-void i915_gem_revoke_fences(struct drm_i915_private *i915)
+void __i915_gem_revoke_fences(struct drm_i915_private *i915)
 {
 	struct i915_ggtt *ggtt = &i915->ggtt;
 	int i;
 
-	mutex_lock(&ggtt->vm.mutex);
+	lockdep_assert_held(&ggtt->vm.mutex);
+
 	for (i = 0; i < ggtt->num_fence_regs; i++) {
 		struct drm_i915_fence_reg *fence = &ggtt->fence_regs[i];
 
@@ -496,23 +497,15 @@ void i915_gem_revoke_fences(struct drm_i915_private *i915)
 		if (fence->vma)
 			i915_vma_revoke_mmap(fence->vma);
 	}
-	mutex_unlock(&ggtt->vm.mutex);
 }
 
-/**
- * i915_gem_restore_fences - restore fence state
- * @i915: i915 device private
- *
- * Restore the hw fence state to match the software tracking again, to be called
- * after a gpu reset and on resume. Note that on runtime suspend we only cancel
- * the fences, to be reacquired by the user later.
- */
-void i915_gem_restore_fences(struct drm_i915_private *i915)
+void __i915_gem_restore_fences(struct drm_i915_private *i915)
 {
 	struct i915_ggtt *ggtt = &i915->ggtt;
 	int i;
 
-	mutex_lock(&ggtt->vm.mutex);
+	lockdep_assert_held(&ggtt->vm.mutex);
+
 	for (i = 0; i < ggtt->num_fence_regs; i++) {
 		struct drm_i915_fence_reg *reg = &ggtt->fence_regs[i];
 		struct i915_vma *vma = reg->vma;
@@ -535,6 +528,24 @@ void i915_gem_restore_fences(struct drm_i915_private *i915)
 		fence_write(reg, vma);
 		reg->vma = vma;
 	}
+}
+
+/**
+ * i915_gem_restore_fences - restore fence state
+ * @i915: i915 device private
+ *
+ * Restore the hw fence state to match the software tracking again, to be called
+ * after a gpu reset and on resume. Note that on runtime suspend we only cancel
+ * the fences, to be reacquired by the user later.
+ */
+void i915_gem_restore_fences(struct drm_i915_private *i915)
+{
+	struct i915_ggtt *ggtt = &i915->ggtt;
+
+	mutex_lock(&ggtt->vm.mutex);
+
+	__i915_gem_restore_fences(i915);
+
 	mutex_unlock(&ggtt->vm.mutex);
 }
 
diff --git a/drivers/gpu/drm/i915/i915_gem_fence_reg.h b/drivers/gpu/drm/i915/i915_gem_fence_reg.h
index 6e66f6b3f851..cd50a9ec36fc 100644
--- a/drivers/gpu/drm/i915/i915_gem_fence_reg.h
+++ b/drivers/gpu/drm/i915/i915_gem_fence_reg.h
@@ -60,8 +60,10 @@ struct drm_i915_fence_reg *
 i915_reserve_fence(struct drm_i915_private *i915);
 void i915_unreserve_fence(struct drm_i915_fence_reg *fence);
 
-void i915_gem_revoke_fences(struct drm_i915_private *i915);
-void i915_gem_restore_fences(struct drm_i915_private *i915);
+void __i915_gem_revoke_fences(struct drm_i915_private *dev_priv);
+void __i915_gem_restore_fences(struct drm_i915_private *dev_priv);
+
+void i915_gem_restore_fences(struct drm_i915_private *dev_priv);
 
 void i915_gem_detect_bit_6_swizzle(struct drm_i915_private *i915);
 void i915_gem_object_do_bit_17_swizzle(struct drm_i915_gem_object *obj,
diff --git a/drivers/gpu/drm/i915/i915_gpu_error.h b/drivers/gpu/drm/i915/i915_gpu_error.h
index f893a4e8b783..9819952a6e49 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.h
+++ b/drivers/gpu/drm/i915/i915_gpu_error.h
@@ -193,6 +193,8 @@ struct i915_gpu_state {
 	struct i915_address_space *active_vm[I915_NUM_ENGINES];
 };
 
+struct i915_gpu_restart;
+
 struct i915_gpu_error {
 	/* For hangcheck timer */
 #define DRM_I915_HANGCHECK_PERIOD 1500 /* in ms */
@@ -243,15 +245,6 @@ struct i915_gpu_error {
 	 * i915_mutex_lock_interruptible()?). I915_RESET_BACKOFF serves a
 	 * secondary role in preventing two concurrent global reset attempts.
 	 *
-	 * #I915_RESET_HANDOFF - To perform the actual GPU reset, we need the
-	 * struct_mutex. We try to acquire the struct_mutex in the reset worker,
-	 * but it may be held by some long running waiter (that we cannot
-	 * interrupt without causing trouble). Once we are ready to do the GPU
-	 * reset, we set the I915_RESET_HANDOFF bit and wakeup any waiters. If
-	 * they already hold the struct_mutex and want to participate they can
-	 * inspect the bit and do the reset directly, otherwise the worker
-	 * waits for the struct_mutex.
-	 *
 	 * #I915_RESET_ENGINE[num_engines] - Since the driver doesn't need to
 	 * acquire the struct_mutex to reset an engine, we need an explicit
 	 * flag to prevent two concurrent reset attempts in the same engine.
@@ -265,20 +258,13 @@ struct i915_gpu_error {
 	 */
 	unsigned long flags;
 #define I915_RESET_BACKOFF	0
-#define I915_RESET_HANDOFF	1
-#define I915_RESET_MODESET	2
+#define I915_RESET_MODESET	1
 #define I915_WEDGED		(BITS_PER_LONG - 1)
 #define I915_RESET_ENGINE	(I915_WEDGED - I915_NUM_ENGINES)
 
 	/** Number of times an engine has been reset */
 	u32 reset_engine_count[I915_NUM_ENGINES];
 
-	/** Set of stalled engines with guilty requests, in the current reset */
-	u32 stalled_mask;
-
-	/** Reason for the current *global* reset */
-	const char *reason;
-
 	/**
 	 * Waitqueue to signal when a hang is detected. Used to for waiters
 	 * to release the struct_mutex for the reset to procede.
@@ -293,6 +279,8 @@ struct i915_gpu_error {
 
 	/* For missed irq/seqno simulation. */
 	unsigned long test_irq_rings;
+
+	struct i915_gpu_restart *restart;
 };
 
 struct drm_i915_error_state_buf {
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index 3d90f3611a34..c9b536584cd1 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -1245,18 +1245,6 @@ static bool __i915_spin_request(const struct i915_request *rq,
 	return false;
 }
 
-static bool __i915_wait_request_check_and_reset(struct i915_request *request)
-{
-	struct i915_gpu_error *error = &request->i915->gpu_error;
-
-	if (likely(!i915_reset_handoff(error)))
-		return false;
-
-	__set_current_state(TASK_RUNNING);
-	i915_reset(request->i915, error->stalled_mask, error->reason);
-	return true;
-}
-
 /**
  * i915_request_wait - wait until execution of request has finished
  * @rq: the request to wait upon
@@ -1282,17 +1270,10 @@ long i915_request_wait(struct i915_request *rq,
 {
 	const int state = flags & I915_WAIT_INTERRUPTIBLE ?
 		TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE;
-	wait_queue_head_t *errq = &rq->i915->gpu_error.wait_queue;
-	DEFINE_WAIT_FUNC(reset, default_wake_function);
 	DEFINE_WAIT_FUNC(exec, default_wake_function);
 	struct intel_wait wait;
 
 	might_sleep();
-#if IS_ENABLED(CONFIG_LOCKDEP)
-	GEM_BUG_ON(debug_locks &&
-		   !!lockdep_is_held(&rq->i915->drm.struct_mutex) !=
-		   !!(flags & I915_WAIT_LOCKED));
-#endif
 	GEM_BUG_ON(timeout < 0);
 
 	if (i915_request_completed(rq))
@@ -1302,10 +1283,7 @@ long i915_request_wait(struct i915_request *rq,
 		return -ETIME;
 
 	trace_i915_request_wait_begin(rq, flags);
-
 	add_wait_queue(&rq->execute, &exec);
-	if (flags & I915_WAIT_LOCKED)
-		add_wait_queue(errq, &reset);
 
 	intel_wait_init(&wait);
 
@@ -1315,10 +1293,6 @@ long i915_request_wait(struct i915_request *rq,
 		if (intel_wait_update_request(&wait, rq))
 			break;
 
-		if (flags & I915_WAIT_LOCKED &&
-		    __i915_wait_request_check_and_reset(rq))
-			continue;
-
 		if (signal_pending_state(state, current)) {
 			timeout = -ERESTARTSYS;
 			goto complete;
@@ -1348,9 +1322,6 @@ long i915_request_wait(struct i915_request *rq,
 		 */
 		goto wakeup;
 
-	if (flags & I915_WAIT_LOCKED)
-		__i915_wait_request_check_and_reset(rq);
-
 	for (;;) {
 		if (signal_pending_state(state, current)) {
 			timeout = -ERESTARTSYS;
@@ -1380,21 +1351,6 @@ long i915_request_wait(struct i915_request *rq,
 		if (__i915_request_irq_complete(rq))
 			break;
 
-		/*
-		 * If the GPU is hung, and we hold the lock, reset the GPU
-		 * and then check for completion. On a full reset, the engine's
-		 * HW seqno will be advanced passed us and we are complete.
-		 * If we do a partial reset, we have to wait for the GPU to
-		 * resume and update the breadcrumb.
-		 *
-		 * If we don't hold the mutex, we can just wait for the worker
-		 * to come along and update the breadcrumb (either directly
-		 * itself, or indirectly by recovering the GPU).
-		 */
-		if (flags & I915_WAIT_LOCKED &&
-		    __i915_wait_request_check_and_reset(rq))
-			continue;
-
 		/* Only spin if we know the GPU is processing this request */
 		if (__i915_spin_request(rq, wait.seqno, state, 2))
 			break;
@@ -1408,8 +1364,6 @@ long i915_request_wait(struct i915_request *rq,
 	intel_engine_remove_wait(rq->engine, &wait);
 complete:
 	__set_current_state(TASK_RUNNING);
-	if (flags & I915_WAIT_LOCKED)
-		remove_wait_queue(errq, &reset);
 	remove_wait_queue(&rq->execute, &exec);
 	trace_i915_request_wait_end(rq);
 
diff --git a/drivers/gpu/drm/i915/i915_reset.c b/drivers/gpu/drm/i915/i915_reset.c
index edf29da15a99..9e9f072d8c7b 100644
--- a/drivers/gpu/drm/i915/i915_reset.c
+++ b/drivers/gpu/drm/i915/i915_reset.c
@@ -15,22 +15,23 @@ static void engine_skip_context(struct i915_request *rq)
 	struct intel_engine_cs *engine = rq->engine;
 	struct i915_gem_context *hung_ctx = rq->gem_context;
 	struct i915_timeline *timeline = rq->timeline;
-	unsigned long flags;
 
+	lockdep_assert_held(&engine->timeline.lock);
 	GEM_BUG_ON(timeline == &engine->timeline);
 
-	spin_lock_irqsave(&engine->timeline.lock, flags);
 	spin_lock(&timeline->lock);
 
-	list_for_each_entry_continue(rq, &engine->timeline.requests, link)
-		if (rq->gem_context == hung_ctx)
-			i915_request_skip(rq, -EIO);
+	if (rq->global_seqno) {
+		list_for_each_entry_continue(rq,
+					     &engine->timeline.requests, link)
+			if (rq->gem_context == hung_ctx)
+				i915_request_skip(rq, -EIO);
+	}
 
 	list_for_each_entry(rq, &timeline->requests, link)
 		i915_request_skip(rq, -EIO);
 
 	spin_unlock(&timeline->lock);
-	spin_unlock_irqrestore(&engine->timeline.lock, flags);
 }
 
 static void client_mark_guilty(struct drm_i915_file_private *file_priv,
@@ -57,7 +58,7 @@ static void client_mark_guilty(struct drm_i915_file_private *file_priv,
 	}
 }
 
-static void context_mark_guilty(struct i915_gem_context *ctx)
+static bool context_mark_guilty(struct i915_gem_context *ctx)
 {
 	unsigned int score;
 	bool banned, bannable;
@@ -70,7 +71,7 @@ static void context_mark_guilty(struct i915_gem_context *ctx)
 
 	/* Cool contexts don't accumulate client ban score */
 	if (!bannable)
-		return;
+		return false;
 
 	if (banned) {
 		DRM_DEBUG_DRIVER("context %s: guilty %d, score %u, banned\n",
@@ -81,6 +82,8 @@ static void context_mark_guilty(struct i915_gem_context *ctx)
 
 	if (!IS_ERR_OR_NULL(ctx->file_priv))
 		client_mark_guilty(ctx->file_priv, ctx);
+
+	return banned;
 }
 
 static void context_mark_innocent(struct i915_gem_context *ctx)
@@ -88,6 +91,21 @@ static void context_mark_innocent(struct i915_gem_context *ctx)
 	atomic_inc(&ctx->active_count);
 }
 
+void i915_reset_request(struct i915_request *rq, bool guilty)
+{
+	lockdep_assert_held(&rq->engine->timeline.lock);
+	GEM_BUG_ON(i915_request_completed(rq));
+
+	if (guilty) {
+		i915_request_skip(rq, -EIO);
+		if (context_mark_guilty(rq->gem_context))
+			engine_skip_context(rq);
+	} else {
+		dma_fence_set_error(&rq->fence, -EAGAIN);
+		context_mark_innocent(rq->gem_context);
+	}
+}
+
 static void gen3_stop_engine(struct intel_engine_cs *engine)
 {
 	struct drm_i915_private *dev_priv = engine->i915;
@@ -482,11 +500,8 @@ int intel_reset_guc(struct drm_i915_private *i915)
  * Ensure irq handler finishes, and not run again.
  * Also return the active request so that we only search for it once.
  */
-static struct i915_request *
-reset_prepare_engine(struct intel_engine_cs *engine)
+static void reset_prepare_engine(struct intel_engine_cs *engine)
 {
-	struct i915_request *rq;
-
 	/*
 	 * During the reset sequence, we must prevent the engine from
 	 * entering RC6. As the context state is undefined until we restart
@@ -495,171 +510,78 @@ reset_prepare_engine(struct intel_engine_cs *engine)
 	 * GPU state upon resume, i.e. fail to restart after a reset.
 	 */
 	intel_uncore_forcewake_get(engine->i915, FORCEWAKE_ALL);
-
-	rq = engine->reset.prepare(engine);
-	if (rq && rq->fence.error == -EIO)
-		rq = ERR_PTR(-EIO); /* Previous reset failed! */
-
-	return rq;
+	engine->reset.prepare(engine);
 }
 
-static int reset_prepare(struct drm_i915_private *i915)
+static void reset_prepare(struct drm_i915_private *i915)
 {
 	struct intel_engine_cs *engine;
-	struct i915_request *rq;
 	enum intel_engine_id id;
-	int err = 0;
-
-	disable_irq(i915->drm.irq);
-
-	for_each_engine(engine, i915, id) {
-		rq = reset_prepare_engine(engine);
-		if (IS_ERR(rq)) {
-			err = PTR_ERR(rq);
-			continue;
-		}
 
-		engine->hangcheck.active_request = rq;
-	}
+	for_each_engine(engine, i915, id)
+		reset_prepare_engine(engine);
 
-	i915_gem_revoke_fences(i915);
 	intel_uc_sanitize(i915);
-
-	return err;
 }
 
-/* Returns the request if it was guilty of the hang */
-static struct i915_request *
-reset_request(struct intel_engine_cs *engine,
-	      struct i915_request *rq,
-	      bool stalled)
+static void gt_reset(struct drm_i915_private *i915, unsigned int stalled_mask)
 {
-	/*
-	 * The guilty request will get skipped on a hung engine.
-	 *
-	 * Users of client default contexts do not rely on logical
-	 * state preserved between batches so it is safe to execute
-	 * queued requests following the hang. Non default contexts
-	 * rely on preserved state, so skipping a batch loses the
-	 * evolution of the state and it needs to be considered corrupted.
-	 * Executing more queued batches on top of corrupted state is
-	 * risky. But we take the risk by trying to advance through
-	 * the queued requests in order to make the client behaviour
-	 * more predictable around resets, by not throwing away random
-	 * amount of batches it has prepared for execution. Sophisticated
-	 * clients can use gem_reset_stats_ioctl and dma fence status
-	 * (exported via sync_file info ioctl on explicit fences) to observe
-	 * when it loses the context state and should rebuild accordingly.
-	 *
-	 * The context ban, and ultimately the client ban, mechanism are safety
-	 * valves if client submission ends up resulting in nothing more than
-	 * subsequent hangs.
-	 */
+	struct intel_engine_cs *engine;
+	enum intel_engine_id id;
 
-	if (i915_request_completed(rq)) {
-		GEM_TRACE("%s pardoned global=%d (fence %llx:%d), current %d\n",
-			  engine->name, rq->global_seqno,
-			  rq->fence.context, rq->fence.seqno,
-			  intel_engine_get_seqno(engine));
-		stalled = false;
-	}
+	mutex_lock(&i915->ggtt.vm.mutex);
+	__i915_gem_revoke_fences(i915);
 
-	if (stalled) {
-		context_mark_guilty(rq->gem_context);
-		i915_request_skip(rq, -EIO);
+	for_each_engine(engine, i915, id)
+		intel_engine_reset(engine, stalled_mask & ENGINE_MASK(id));
 
-		/* If this context is now banned, skip all pending requests. */
-		if (i915_gem_context_is_banned(rq->gem_context))
-			engine_skip_context(rq);
-	} else {
-		/*
-		 * Since this is not the hung engine, it may have advanced
-		 * since the hang declaration. Double check by refinding
-		 * the active request at the time of the reset.
-		 */
-		rq = i915_gem_find_active_request(engine);
-		if (rq) {
-			unsigned long flags;
-
-			context_mark_innocent(rq->gem_context);
-			dma_fence_set_error(&rq->fence, -EAGAIN);
-
-			/* Rewind the engine to replay the incomplete rq */
-			spin_lock_irqsave(&engine->timeline.lock, flags);
-			rq = list_prev_entry(rq, link);
-			if (&rq->link == &engine->timeline.requests)
-				rq = NULL;
-			spin_unlock_irqrestore(&engine->timeline.lock, flags);
-		}
-	}
-
-	return rq;
+	__i915_gem_restore_fences(i915);
+	mutex_unlock(&i915->ggtt.vm.mutex);
 }
 
-static void reset_engine(struct intel_engine_cs *engine,
-			 struct i915_request *rq,
-			 bool stalled)
+static void reset_finish_engine(struct intel_engine_cs *engine)
 {
-	/*
-	 * Make sure this write is visible before we re-enable the interrupt
-	 * handlers on another CPU, as tasklet_enable() resolves to just
-	 * a compiler barrier which is insufficient for our purpose here.
-	 */
-	smp_store_mb(engine->irq_posted, 0);
-
-	if (rq)
-		rq = reset_request(engine, rq, stalled);
-
-	/* Setup the CS to resume from the breadcrumb of the hung request */
-	engine->reset.reset(engine, rq);
+	engine->reset.finish(engine);
+	intel_uncore_forcewake_put(engine->i915, FORCEWAKE_ALL);
 }
 
-static void gt_reset(struct drm_i915_private *i915, unsigned int stalled_mask)
+struct i915_gpu_restart {
+	struct work_struct work;
+	struct drm_i915_private *i915;
+};
+
+static void restart_work(struct work_struct *work)
 {
+	struct i915_gpu_restart *arg = container_of(work, typeof(*arg), work);
+	struct drm_i915_private *i915 = arg->i915;
 	struct intel_engine_cs *engine;
 	enum intel_engine_id id;
 
-	lockdep_assert_held(&i915->drm.struct_mutex);
+	intel_runtime_pm_get(i915);
+	mutex_lock(&i915->drm.struct_mutex);
 
-	i915_retire_requests(i915);
+	smp_store_mb(i915->gpu_error.restart, NULL);
 
 	for_each_engine(engine, i915, id) {
-		struct intel_context *ce;
-
-		reset_engine(engine,
-			     engine->hangcheck.active_request,
-			     stalled_mask & ENGINE_MASK(id));
-		ce = fetch_and_zero(&engine->last_retired_context);
-		if (ce)
-			intel_context_unpin(ce);
+		struct i915_request *rq;
 
 		/*
 		 * Ostensibily, we always want a context loaded for powersaving,
 		 * so if the engine is idle after the reset, send a request
 		 * to load our scratch kernel_context.
-		 *
-		 * More mysteriously, if we leave the engine idle after a reset,
-		 * the next userspace batch may hang, with what appears to be
-		 * an incoherent read by the CS (presumably stale TLB). An
-		 * empty request appears sufficient to paper over the glitch.
 		 */
-		if (intel_engine_is_idle(engine)) {
-			struct i915_request *rq;
+		if (!intel_engine_is_idle(engine))
+			continue;
 
-			rq = i915_request_alloc(engine, i915->kernel_context);
-			if (!IS_ERR(rq))
-				i915_request_add(rq);
-		}
+		rq = i915_request_alloc(engine, i915->kernel_context);
+		if (!IS_ERR(rq))
+			i915_request_add(rq);
 	}
 
-	i915_gem_restore_fences(i915);
-}
-
-static void reset_finish_engine(struct intel_engine_cs *engine)
-{
-	engine->reset.finish(engine);
+	mutex_unlock(&i915->drm.struct_mutex);
+	intel_runtime_pm_put(i915);
 
-	intel_uncore_forcewake_put(engine->i915, FORCEWAKE_ALL);
+	kfree(arg);
 }
 
 static void reset_finish(struct drm_i915_private *i915)
@@ -667,14 +589,26 @@ static void reset_finish(struct drm_i915_private *i915)
 	struct intel_engine_cs *engine;
 	enum intel_engine_id id;
 
-	lockdep_assert_held(&i915->drm.struct_mutex);
-
-	for_each_engine(engine, i915, id) {
-		engine->hangcheck.active_request = NULL;
+	for_each_engine(engine, i915, id)
 		reset_finish_engine(engine);
-	}
 
-	enable_irq(i915->drm.irq);
+	/*
+	 * Following the reset, ensure that we always reload context for
+	 * powersaving, and to correct engine->last_retired_context.
+	 */
+	if (!i915_terminally_wedged(&i915->gpu_error) &&
+	    !READ_ONCE(i915->gpu_error.restart)) {
+		struct i915_gpu_restart *arg;
+
+		arg = kmalloc(sizeof(*arg), GFP_KERNEL);
+		if (arg) {
+			arg->i915 = i915;
+			INIT_WORK(&arg->work, restart_work);
+
+			WRITE_ONCE(i915->gpu_error.restart, arg);
+			queue_work(i915->wq, &arg->work);
+		}
+	}
 }
 
 static void nop_submit_request(struct i915_request *rq)
@@ -784,7 +718,6 @@ bool i915_gem_unset_wedged(struct drm_i915_private *i915)
 {
 	struct i915_timeline *tl;
 
-	lockdep_assert_held(&i915->drm.struct_mutex);
 	if (!test_bit(I915_WEDGED, &i915->gpu_error.flags))
 		return true;
 
@@ -802,9 +735,9 @@ bool i915_gem_unset_wedged(struct drm_i915_private *i915)
 	 */
 	list_for_each_entry(tl, &i915->gt.timelines, link) {
 		struct i915_request *rq;
+		long timeout;
 
-		rq = i915_gem_active_peek(&tl->last_request,
-					  &i915->drm.struct_mutex);
+		rq = i915_gem_active_get_unlocked(&tl->last_request);
 		if (!rq)
 			continue;
 
@@ -819,12 +752,12 @@ bool i915_gem_unset_wedged(struct drm_i915_private *i915)
 		 * and when the seqno passes the fence, the signaler
 		 * then signals the fence waking us up).
 		 */
-		if (dma_fence_default_wait(&rq->fence, true,
-					   MAX_SCHEDULE_TIMEOUT) < 0)
+		timeout = dma_fence_default_wait(&rq->fence, true,
+						 MAX_SCHEDULE_TIMEOUT);
+		i915_request_put(rq);
+		if (timeout < 0)
 			return false;
 	}
-	i915_retire_requests(i915);
-	GEM_BUG_ON(i915->gt.active_requests);
 
 	/*
 	 * Undo nop_submit_request. We prevent all new i915 requests from
@@ -836,7 +769,6 @@ bool i915_gem_unset_wedged(struct drm_i915_private *i915)
 	 * context and do not require stop_machine().
 	 */
 	intel_engines_reset_default_submission(i915);
-	i915_gem_contexts_lost(i915);
 
 	GEM_TRACE("end\n");
 
@@ -876,25 +808,17 @@ void i915_reset(struct drm_i915_private *i915,
 	GEM_TRACE("flags=%lx\n", error->flags);
 
 	might_sleep();
-	lockdep_assert_held(&i915->drm.struct_mutex);
 	GEM_BUG_ON(!test_bit(I915_RESET_BACKOFF, &error->flags));
 
-	if (!test_bit(I915_RESET_HANDOFF, &error->flags))
-		return;
-
 	/* Clear any previous failed attempts at recovery. Time to try again. */
 	if (!i915_gem_unset_wedged(i915))
-		goto wakeup;
+		return;
 
 	if (reason)
 		dev_notice(i915->drm.dev, "Resetting chip for %s\n", reason);
 	error->reset_count++;
 
-	ret = reset_prepare(i915);
-	if (ret) {
-		dev_err(i915->drm.dev, "GPU recovery failed\n");
-		goto taint;
-	}
+	reset_prepare(i915);
 
 	if (!intel_has_gpu_reset(i915)) {
 		if (i915_modparams.reset)
@@ -951,9 +875,6 @@ void i915_reset(struct drm_i915_private *i915,
 
 finish:
 	reset_finish(i915);
-wakeup:
-	clear_bit(I915_RESET_HANDOFF, &error->flags);
-	wake_up_bit(&error->flags, I915_RESET_HANDOFF);
 	return;
 
 taint:
@@ -972,7 +893,6 @@ void i915_reset(struct drm_i915_private *i915,
 	add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
 error:
 	i915_gem_set_wedged(i915);
-	i915_retire_requests(i915);
 	goto finish;
 }
 
@@ -998,18 +918,16 @@ static inline int intel_gt_reset_engine(struct drm_i915_private *i915,
 int i915_reset_engine(struct intel_engine_cs *engine, const char *msg)
 {
 	struct i915_gpu_error *error = &engine->i915->gpu_error;
-	struct i915_request *active_request;
 	int ret;
 
 	GEM_TRACE("%s flags=%lx\n", engine->name, error->flags);
 	GEM_BUG_ON(!test_bit(I915_RESET_ENGINE + engine->id, &error->flags));
 
-	active_request = reset_prepare_engine(engine);
-	if (IS_ERR_OR_NULL(active_request)) {
-		/* Either the previous reset failed, or we pardon the reset. */
-		ret = PTR_ERR(active_request);
-		goto out;
-	}
+	if (i915_seqno_passed(intel_engine_get_seqno(engine),
+			      intel_engine_last_submit(engine)))
+		return 0;
+
+	reset_prepare_engine(engine);
 
 	if (msg)
 		dev_notice(engine->i915->drm.dev,
@@ -1033,7 +951,7 @@ int i915_reset_engine(struct intel_engine_cs *engine, const char *msg)
 	 * active request and can drop it, adjust head to skip the offending
 	 * request to resume executing remaining requests in the queue.
 	 */
-	reset_engine(engine, active_request, true);
+	intel_engine_reset(engine, true);
 
 	/*
 	 * The engine and its registers (and workarounds in case of render)
@@ -1109,30 +1027,7 @@ static void i915_reset_device(struct drm_i915_private *i915,
 	i915_wedge_on_timeout(&w, i915, 5 * HZ) {
 		intel_prepare_reset(i915);
 
-		error->reason = reason;
-		error->stalled_mask = engine_mask;
-
-		/* Signal that locked waiters should reset the GPU */
-		smp_mb__before_atomic();
-		set_bit(I915_RESET_HANDOFF, &error->flags);
-		wake_up_all(&error->wait_queue);
-
-		/*
-		 * Wait for anyone holding the lock to wakeup, without
-		 * blocking indefinitely on struct_mutex.
-		 */
-		do {
-			if (mutex_trylock(&i915->drm.struct_mutex)) {
-				i915_reset(i915, engine_mask, reason);
-				mutex_unlock(&i915->drm.struct_mutex);
-			}
-		} while (wait_on_bit_timeout(&error->flags,
-					     I915_RESET_HANDOFF,
-					     TASK_UNINTERRUPTIBLE,
-					     1));
-
-		error->stalled_mask = 0;
-		error->reason = NULL;
+		i915_reset(i915, engine_mask, reason);
 
 		intel_finish_reset(i915);
 	}
@@ -1269,3 +1164,21 @@ void i915_handle_error(struct drm_i915_private *i915,
 out:
 	intel_runtime_pm_put(i915);
 }
+
+bool i915_reset_flush(struct drm_i915_private *i915)
+{
+	int err;
+
+	cancel_delayed_work_sync(&i915->gpu_error.hangcheck_work);
+
+	flush_workqueue(i915->wq);
+	GEM_BUG_ON(READ_ONCE(i915->gpu_error.restart));
+
+	mutex_lock(&i915->drm.struct_mutex);
+	err = i915_gem_wait_for_idle(i915,
+				     I915_WAIT_LOCKED |
+				     I915_WAIT_FOR_IDLE_BOOST);
+	mutex_unlock(&i915->drm.struct_mutex);
+
+	return !err;
+}
diff --git a/drivers/gpu/drm/i915/i915_reset.h b/drivers/gpu/drm/i915/i915_reset.h
index 09422c4772dd..39d258a82e97 100644
--- a/drivers/gpu/drm/i915/i915_reset.h
+++ b/drivers/gpu/drm/i915/i915_reset.h
@@ -27,6 +27,9 @@ void i915_reset(struct drm_i915_private *i915,
 int i915_reset_engine(struct intel_engine_cs *engine,
 		      const char *reason);
 
+void i915_reset_request(struct i915_request *rq, bool guilty);
+bool i915_reset_flush(struct drm_i915_private *i915);
+
 bool intel_has_gpu_reset(struct drm_i915_private *i915);
 bool intel_has_reset_engine(struct drm_i915_private *i915);
 
diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index 210794ea230d..9856dbc7f3ff 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -1084,10 +1084,8 @@ void intel_engines_sanitize(struct drm_i915_private *i915)
 
 	GEM_TRACE("\n");
 
-	for_each_engine(engine, i915, id) {
-		if (engine->reset.reset)
-			engine->reset.reset(engine, NULL);
-	}
+	for_each_engine(engine, i915, id)
+		intel_engine_reset(engine, false);
 }
 
 /**
diff --git a/drivers/gpu/drm/i915/intel_guc_submission.c b/drivers/gpu/drm/i915/intel_guc_submission.c
index f3945258fe1b..326de158dae6 100644
--- a/drivers/gpu/drm/i915/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/intel_guc_submission.c
@@ -814,8 +814,7 @@ static void guc_submission_tasklet(unsigned long data)
 		guc_dequeue(engine);
 }
 
-static struct i915_request *
-guc_reset_prepare(struct intel_engine_cs *engine)
+static void guc_reset_prepare(struct intel_engine_cs *engine)
 {
 	struct intel_engine_execlists * const execlists = &engine->execlists;
 
@@ -841,8 +840,6 @@ guc_reset_prepare(struct intel_engine_cs *engine)
 	 */
 	if (engine->i915->guc.preempt_wq)
 		flush_workqueue(engine->i915->guc.preempt_wq);
-
-	return i915_gem_find_active_request(engine);
 }
 
 /*
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index ab89dabc2965..7b4dbe8746a4 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -137,6 +137,7 @@
 #include <drm/i915_drm.h>
 #include "i915_drv.h"
 #include "i915_gem_render_state.h"
+#include "i915_reset.h"
 #include "i915_vgpu.h"
 #include "intel_lrc_reg.h"
 #include "intel_mocs.h"
@@ -325,9 +326,10 @@ static void unwind_wa_tail(struct i915_request *rq)
 	assert_ring_tail_valid(rq->ring, rq->tail);
 }
 
-static void __unwind_incomplete_requests(struct intel_engine_cs *engine)
+static struct i915_request *
+__unwind_incomplete_requests(struct intel_engine_cs *engine)
 {
-	struct i915_request *rq, *rn;
+	struct i915_request *rq, *rn, *active = NULL;
 	struct i915_priolist *uninitialized_var(p);
 	int last_prio = I915_PRIORITY_INVALID;
 
@@ -337,7 +339,7 @@ static void __unwind_incomplete_requests(struct intel_engine_cs *engine)
 					 &engine->timeline.requests,
 					 link) {
 		if (i915_request_completed(rq))
-			return;
+			break;
 
 		__i915_request_unsubmit(rq);
 		unwind_wa_tail(rq);
@@ -350,7 +352,11 @@ static void __unwind_incomplete_requests(struct intel_engine_cs *engine)
 
 		GEM_BUG_ON(p->priority != rq_prio(rq));
 		list_add(&rq->sched.link, &p->requests);
+
+		active = rq;
 	}
+
+	return active;
 }
 
 void
@@ -1902,14 +1908,13 @@ static int gen9_init_render_ring(struct intel_engine_cs *engine)
 	return 0;
 }
 
-static struct i915_request *
-execlists_reset_prepare(struct intel_engine_cs *engine)
+static void execlists_reset_prepare(struct intel_engine_cs *engine)
 {
 	struct intel_engine_execlists * const execlists = &engine->execlists;
-	struct i915_request *request, *active;
 	unsigned long flags;
 
-	GEM_TRACE("%s\n", engine->name);
+	GEM_TRACE("%s, tasklet disabled?=%d\n",
+		  engine->name, atomic_read(&execlists->tasklet.count));
 
 	/*
 	 * Prevent request submission to the hardware until we have
@@ -1921,59 +1926,20 @@ execlists_reset_prepare(struct intel_engine_cs *engine)
 	 * prevents the race.
 	 */
 	__tasklet_disable_sync_once(&execlists->tasklet);
+	GEM_BUG_ON(!reset_in_progress(execlists));
 
+	/* And flush any current direct submission. */
 	spin_lock_irqsave(&engine->timeline.lock, flags);
-
-	/*
-	 * We want to flush the pending context switches, having disabled
-	 * the tasklet above, we can assume exclusive access to the execlists.
-	 * For this allows us to catch up with an inflight preemption event,
-	 * and avoid blaming an innocent request if the stall was due to the
-	 * preemption itself.
-	 */
-	process_csb(engine);
-
-	/*
-	 * The last active request can then be no later than the last request
-	 * now in ELSP[0]. So search backwards from there, so that if the GPU
-	 * has advanced beyond the last CSB update, it will be pardoned.
-	 */
-	active = NULL;
-	request = port_request(execlists->port);
-	if (request) {
-		/*
-		 * Prevent the breadcrumb from advancing before we decide
-		 * which request is currently active.
-		 */
-		intel_engine_stop_cs(engine);
-
-		list_for_each_entry_from_reverse(request,
-						 &engine->timeline.requests,
-						 link) {
-			if (__i915_request_completed(request,
-						     request->global_seqno))
-				break;
-
-			active = request;
-		}
-	}
-
 	spin_unlock_irqrestore(&engine->timeline.lock, flags);
-
-	return active;
 }
 
-static void execlists_reset(struct intel_engine_cs *engine,
-			    struct i915_request *request)
+static void execlists_reset(struct intel_engine_cs *engine, bool stalled)
 {
 	struct intel_engine_execlists * const execlists = &engine->execlists;
+	struct i915_request *rq;
 	unsigned long flags;
 	u32 *regs;
 
-	GEM_TRACE("%s request global=%x, current=%d\n",
-		  engine->name, request ? request->global_seqno : 0,
-		  intel_engine_get_seqno(engine));
-
 	spin_lock_irqsave(&engine->timeline.lock, flags);
 
 	/*
@@ -1989,12 +1955,16 @@ static void execlists_reset(struct intel_engine_cs *engine,
 	reset_irq(engine);
 
 	/* Push back any incomplete requests for replay after the reset. */
-	__unwind_incomplete_requests(engine);
+	rq = __unwind_incomplete_requests(engine);
 
 	/* Following the reset, we need to reload the CSB read/write pointers */
 	reset_csb_pointers(&engine->execlists);
 
-	spin_unlock_irqrestore(&engine->timeline.lock, flags);
+	GEM_TRACE("%s request global=%x, current=%d\n",
+		  engine->name, rq ? rq->global_seqno : 0,
+		  intel_engine_get_seqno(engine));
+	if (!rq)
+		goto out_unlock;
 
 	/*
 	 * If the request was innocent, we leave the request in the ELSP
@@ -2007,8 +1977,9 @@ static void execlists_reset(struct intel_engine_cs *engine,
 	 * and have to at least restore the RING register in the context
 	 * image back to the expected values to skip over the guilty request.
 	 */
-	if (!request || request->fence.error != -EIO)
-		return;
+	i915_reset_request(rq, stalled);
+	if (!stalled)
+		goto out_unlock;
 
 	/*
 	 * We want a simple context + ring to execute the breadcrumb update.
@@ -2018,25 +1989,23 @@ static void execlists_reset(struct intel_engine_cs *engine,
 	 * future request will be after userspace has had the opportunity
 	 * to recreate its own state.
 	 */
-	regs = request->hw_context->lrc_reg_state;
+	regs = rq->hw_context->lrc_reg_state;
 	if (engine->pinned_default_state) {
 		memcpy(regs, /* skip restoring the vanilla PPHWSP */
 		       engine->pinned_default_state + LRC_STATE_PN * PAGE_SIZE,
 		       engine->context_size - PAGE_SIZE);
 	}
-	execlists_init_reg_state(regs,
-				 request->gem_context, engine, request->ring);
+	execlists_init_reg_state(regs, rq->gem_context, engine, rq->ring);
 
 	/* Move the RING_HEAD onto the breadcrumb, past the hanging batch */
-	regs[CTX_RING_BUFFER_START + 1] = i915_ggtt_offset(request->ring->vma);
+	regs[CTX_RING_BUFFER_START + 1] = i915_ggtt_offset(rq->ring->vma);
 
-	request->ring->head = intel_ring_wrap(request->ring, request->postfix);
-	regs[CTX_RING_HEAD + 1] = request->ring->head;
+	rq->ring->head = intel_ring_wrap(rq->ring, rq->postfix);
+	regs[CTX_RING_HEAD + 1] = rq->ring->head;
+	intel_ring_update_space(rq->ring);
 
-	intel_ring_update_space(request->ring);
-
-	/* Reset WaIdleLiteRestore:bdw,skl as well */
-	unwind_wa_tail(request);
+out_unlock:
+	spin_unlock_irqrestore(&engine->timeline.lock, flags);
 }
 
 static void execlists_reset_finish(struct intel_engine_cs *engine)
@@ -2056,6 +2025,7 @@ static void execlists_reset_finish(struct intel_engine_cs *engine)
 	 * serialising multiple attempts to reset so that we know that we
 	 * are the only one manipulating tasklet state.
 	 */
+	GEM_BUG_ON(!reset_in_progress(execlists));
 	__tasklet_enable_sync_once(&execlists->tasklet);
 
 	GEM_TRACE("%s\n", engine->name);
diff --git a/drivers/gpu/drm/i915/intel_overlay.c b/drivers/gpu/drm/i915/intel_overlay.c
index c2f10d899329..371eb3dbedc0 100644
--- a/drivers/gpu/drm/i915/intel_overlay.c
+++ b/drivers/gpu/drm/i915/intel_overlay.c
@@ -501,8 +501,6 @@ void intel_overlay_reset(struct drm_i915_private *dev_priv)
 	if (!overlay)
 		return;
 
-	intel_overlay_release_old_vid(overlay);
-
 	overlay->old_xscale = 0;
 	overlay->old_yscale = 0;
 	overlay->crtc = NULL;
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 700f94c371b3..2637e3db0e80 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -34,6 +34,7 @@
 
 #include "i915_drv.h"
 #include "i915_gem_render_state.h"
+#include "i915_reset.h"
 #include "i915_trace.h"
 #include "intel_drv.h"
 #include "intel_workarounds.h"
@@ -535,54 +536,82 @@ static int init_ring_common(struct intel_engine_cs *engine)
 	return ret;
 }
 
-static struct i915_request *reset_prepare(struct intel_engine_cs *engine)
+static void reset_prepare(struct intel_engine_cs *engine)
 {
 	intel_engine_stop_cs(engine);
 
 	if (engine->irq_seqno_barrier)
 		engine->irq_seqno_barrier(engine);
-
-	return i915_gem_find_active_request(engine);
 }
 
-static void skip_request(struct i915_request *rq)
+static void reset_ring(struct intel_engine_cs *engine, bool stalled)
 {
-	void *vaddr = rq->ring->vaddr;
+	struct i915_timeline *tl = &engine->timeline;
+	struct i915_request *pos, *rq;
+	unsigned long flags;
 	u32 head;
 
-	head = rq->infix;
-	if (rq->postfix < head) {
-		memset32(vaddr + head, MI_NOOP,
-			 (rq->ring->size - head) / sizeof(u32));
-		head = 0;
+	rq = NULL;
+	spin_lock_irqsave(&tl->lock, flags);
+	list_for_each_entry(pos, &tl->requests, link) {
+		if (!__i915_request_completed(pos, pos->global_seqno)) {
+			rq = pos;
+			break;
+		}
 	}
-	memset32(vaddr + head, MI_NOOP, (rq->postfix - head) / sizeof(u32));
-}
-
-static void reset_ring(struct intel_engine_cs *engine, struct i915_request *rq)
-{
-	GEM_TRACE("%s seqno=%x\n", engine->name, rq ? rq->global_seqno : 0);
 
+	GEM_TRACE("%s seqno=%x, stalled? %s\n",
+		  engine->name,
+		  rq ? rq->global_seqno : 0,
+		  yesno(stalled));
 	/*
-	 * Try to restore the logical GPU state to match the continuation
-	 * of the request queue. If we skip the context/PD restore, then
-	 * the next request may try to execute assuming that its context
-	 * is valid and loaded on the GPU and so may try to access invalid
-	 * memory, prompting repeated GPU hangs.
+	 * The guilty request will get skipped on a hung engine.
 	 *
-	 * If the request was guilty, we still restore the logical state
-	 * in case the next request requires it (e.g. the aliasing ppgtt),
-	 * but skip over the hung batch.
+	 * Users of client default contexts do not rely on logical
+	 * state preserved between batches so it is safe to execute
+	 * queued requests following the hang. Non default contexts
+	 * rely on preserved state, so skipping a batch loses the
+	 * evolution of the state and it needs to be considered corrupted.
+	 * Executing more queued batches on top of corrupted state is
+	 * risky. But we take the risk by trying to advance through
+	 * the queued requests in order to make the client behaviour
+	 * more predictable around resets, by not throwing away random
+	 * amount of batches it has prepared for execution. Sophisticated
+	 * clients can use gem_reset_stats_ioctl and dma fence status
+	 * (exported via sync_file info ioctl on explicit fences) to observe
+	 * when it loses the context state and should rebuild accordingly.
 	 *
-	 * If the request was innocent, we try to replay the request with
-	 * the restored context.
+	 * The context ban, and ultimately the client ban, mechanism are safety
+	 * valves if client submission ends up resulting in nothing more than
+	 * subsequent hangs.
 	 */
+
 	if (rq) {
-		/* If the rq hung, jump to its breadcrumb and skip the batch */
-		rq->ring->head = intel_ring_wrap(rq->ring, rq->head);
-		if (rq->fence.error == -EIO)
-			skip_request(rq);
+		/*
+		 * Try to restore the logical GPU state to match the
+		 * continuation of the request queue. If we skip the
+		 * context/PD restore, then the next request may try to execute
+		 * assuming that its context is valid and loaded on the GPU and
+		 * so may try to access invalid memory, prompting repeated GPU
+		 * hangs.
+		 *
+		 * If the request was guilty, we still restore the logical
+		 * state in case the next request requires it (e.g. the
+		 * aliasing ppgtt), but skip over the hung batch.
+		 *
+		 * If the request was innocent, we try to replay the request
+		 * with the restored context.
+		 */
+		i915_reset_request(rq, stalled);
+
+		GEM_BUG_ON(rq->ring != engine->buffer);
+		head = rq->head;
+	} else {
+		head = engine->buffer->tail;
 	}
+	engine->buffer->head = intel_ring_wrap(engine->buffer, head);
+
+	spin_unlock_irqrestore(&tl->lock, flags);
 }
 
 static void reset_finish(struct intel_engine_cs *engine)
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index ce6cc2a6cf7a..98675fa8e8cc 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -121,7 +121,6 @@ struct intel_engine_hangcheck {
 	unsigned long action_timestamp;
 	int deadlock;
 	struct intel_instdone instdone;
-	struct i915_request *active_request;
 	bool stalled:1;
 	bool wedged:1;
 };
@@ -446,9 +445,8 @@ struct intel_engine_cs {
 	int		(*init_hw)(struct intel_engine_cs *engine);
 
 	struct {
-		struct i915_request *(*prepare)(struct intel_engine_cs *engine);
-		void (*reset)(struct intel_engine_cs *engine,
-			      struct i915_request *rq);
+		void (*prepare)(struct intel_engine_cs *engine);
+		void (*reset)(struct intel_engine_cs *engine, bool stalled);
 		void (*finish)(struct intel_engine_cs *engine);
 	} reset;
 
@@ -1070,6 +1068,13 @@ gen8_emit_ggtt_write(u32 *cs, u32 value, u32 gtt_offset)
 	return cs;
 }
 
+static inline void intel_engine_reset(struct intel_engine_cs *engine,
+				      bool stalled)
+{
+	if (engine->reset.reset)
+		engine->reset.reset(engine, stalled);
+}
+
 void intel_engines_sanitize(struct drm_i915_private *i915);
 
 bool intel_engine_is_idle(struct intel_engine_cs *engine);
diff --git a/drivers/gpu/drm/i915/selftests/intel_hangcheck.c b/drivers/gpu/drm/i915/selftests/intel_hangcheck.c
index e11df2743704..e522a02343d5 100644
--- a/drivers/gpu/drm/i915/selftests/intel_hangcheck.c
+++ b/drivers/gpu/drm/i915/selftests/intel_hangcheck.c
@@ -390,7 +390,6 @@ static int igt_global_reset(void *arg)
 	/* Check that we can issue a global GPU reset */
 
 	global_reset_lock(i915);
-	set_bit(I915_RESET_HANDOFF, &i915->gpu_error.flags);
 
 	mutex_lock(&i915->drm.struct_mutex);
 	reset_count = i915_reset_count(&i915->gpu_error);
@@ -403,7 +402,6 @@ static int igt_global_reset(void *arg)
 	}
 	mutex_unlock(&i915->drm.struct_mutex);
 
-	GEM_BUG_ON(test_bit(I915_RESET_HANDOFF, &i915->gpu_error.flags));
 	global_reset_unlock(i915);
 
 	if (i915_terminally_wedged(&i915->gpu_error))
@@ -513,7 +511,7 @@ static int __igt_reset_engine(struct drm_i915_private *i915, bool active)
 				break;
 			}
 
-			if (!wait_for_idle(engine)) {
+			if (!i915_reset_flush(i915)) {
 				struct drm_printer p =
 					drm_info_printer(i915->drm.dev);
 
@@ -905,20 +903,13 @@ static int igt_reset_engines(void *arg)
 	return 0;
 }
 
-static u32 fake_hangcheck(struct i915_request *rq, u32 mask)
+static u32 fake_hangcheck(struct drm_i915_private *i915, u32 mask)
 {
-	struct i915_gpu_error *error = &rq->i915->gpu_error;
-	u32 reset_count = i915_reset_count(error);
+	u32 count = i915_reset_count(&i915->gpu_error);
 
-	error->stalled_mask = mask;
+	i915_reset(i915, mask, NULL);
 
-	/* set_bit() must be after we have setup the backchannel (mask) */
-	smp_mb__before_atomic();
-	set_bit(I915_RESET_HANDOFF, &error->flags);
-
-	wake_up_all(&error->wait_queue);
-
-	return reset_count;
+	return count;
 }
 
 static int igt_wait_reset(void *arg)
@@ -964,7 +955,7 @@ static int igt_wait_reset(void *arg)
 		goto out_rq;
 	}
 
-	reset_count = fake_hangcheck(rq, ALL_ENGINES);
+	reset_count = fake_hangcheck(i915, ALL_ENGINES);
 
 	timeout = i915_request_wait(rq, I915_WAIT_LOCKED, 10);
 	if (timeout < 0) {
@@ -974,7 +965,6 @@ static int igt_wait_reset(void *arg)
 		goto out_rq;
 	}
 
-	GEM_BUG_ON(test_bit(I915_RESET_HANDOFF, &i915->gpu_error.flags));
 	if (i915_reset_count(&i915->gpu_error) == reset_count) {
 		pr_err("No GPU reset recorded!\n");
 		err = -EINVAL;
@@ -1100,12 +1090,7 @@ static int igt_reset_queue(void *arg)
 				goto fini;
 			}
 
-			reset_count = fake_hangcheck(prev, ENGINE_MASK(id));
-
-			i915_reset(i915, ENGINE_MASK(id), NULL);
-
-			GEM_BUG_ON(test_bit(I915_RESET_HANDOFF,
-					    &i915->gpu_error.flags));
+			reset_count = fake_hangcheck(i915, ENGINE_MASK(id));
 
 			if (prev->fence.error != -EIO) {
 				pr_err("GPU reset not recorded on hanging request [fence.error=%d]!\n",
-- 
2.18.0



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