msm: kgsl: Keep the context alive until its fences signal

The context is currently kept alive until all its fences are
released. This means that we do not destroy a context until all
the fence fds associated with it are closed by userspace, which may
be a long time. Instead, remove the timeline's refcount on its
context when it is detached. This permits the context to be freed
once all its fences signal.

Change-Id: Ifc5dd55980358ddbb4d3f6220d8b5d9f725aed1b
Signed-off-by: Lynus Vaz <lvaz@codeaurora.org>
Signed-off-by: Hareesh Gundu <hareeshg@codeaurora.org>

drivers/gpu/msm/kgsl.c

@@ -758,8 +758,7 @@ void kgsl_context_detach(struct kgsl_context *context)
 	/* Remove the event group from the list */
 	kgsl_del_event_group(device, &context->events);
 
-	kgsl_sync_timeline_put(context->ktimeline);
-
+	kgsl_sync_timeline_detach(context->ktimeline);
 	kgsl_context_put(context);
 }
 
@@ -778,6 +777,8 @@ kgsl_context_destroy(struct kref *kref)
 	 */
 	BUG_ON(!kgsl_context_detached(context));
 
+	kgsl_sync_timeline_put(context->ktimeline);
+
 	write_lock(&device->context_lock);
 	if (context->id != KGSL_CONTEXT_INVALID) {
 
@@ -801,7 +802,6 @@ kgsl_context_destroy(struct kref *kref)
 		context->id = KGSL_CONTEXT_INVALID;
 	}
 	write_unlock(&device->context_lock);
-	kgsl_sync_timeline_destroy(context);
 	kgsl_process_private_put(context->proc_priv);
 
 	device->ftbl->drawctxt_destroy(context);

drivers/gpu/msm/kgsl_sync.c

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0-only
 /*
- * Copyright (c) 2012-2019, The Linux Foundation. All rights reserved.
+ * Copyright (c) 2012-2019, 2021, The Linux Foundation. All rights reserved.
  */
 
 #include <linux/file.h>
@@ -249,27 +249,41 @@ static void kgsl_sync_timeline_value_str(struct dma_fence *fence,
 {
 	struct kgsl_sync_fence *kfence = (struct kgsl_sync_fence *)fence;
 	struct kgsl_sync_timeline *ktimeline = kfence->parent;
+	struct kgsl_context *context = NULL;
+	unsigned long flags;
+	int ret = 0;
 
-	unsigned int timestamp_retired = 0;
-	unsigned int timestamp_queued = 0;
+	unsigned int timestamp_retired;
+	unsigned int timestamp_queued;
 
 	if (!kref_get_unless_zero(&ktimeline->kref))
 		return;
+	if (!ktimeline->device)
+		goto put_timeline;
 
-	/*
-	 * ktimeline->device might be NULL here but kgsl_readtimestamp()
-	 * will handle that correctly
-	 */
-	kgsl_readtimestamp(ktimeline->device, ktimeline->context,
-		KGSL_TIMESTAMP_RETIRED, &timestamp_retired);
+	spin_lock_irqsave(&ktimeline->lock, flags);
+	ret = _kgsl_context_get(ktimeline->context);
+	context = ret ? ktimeline->context : NULL;
+	spin_unlock_irqrestore(&ktimeline->lock, flags);
 
-	kgsl_readtimestamp(ktimeline->device, ktimeline->context,
-		KGSL_TIMESTAMP_QUEUED, &timestamp_queued);
+	/* Get the last signaled timestamp if the context is not valid */
+	timestamp_queued = ktimeline->last_timestamp;
+	timestamp_retired = timestamp_queued;
+	if (context) {
+		kgsl_readtimestamp(ktimeline->device, context,
+			KGSL_TIMESTAMP_RETIRED, &timestamp_retired);
+
+		kgsl_readtimestamp(ktimeline->device, context,
+			KGSL_TIMESTAMP_QUEUED, &timestamp_queued);
+
+		kgsl_context_put(context);
+	}
 
 	snprintf(str, size, "%u queued:%u retired:%u",
 		ktimeline->last_timestamp,
 		timestamp_queued, timestamp_retired);
 
+put_timeline:
 	kgsl_sync_timeline_put(ktimeline);
 }
 
@@ -298,7 +312,7 @@ int kgsl_sync_timeline_create(struct kgsl_context *context)
 {
 	struct kgsl_sync_timeline *ktimeline;
 
-	/* Put context when timeline is released */
+	/* Put context at detach time */
 	if (!_kgsl_context_get(context))
 		return -ENOENT;
 
@@ -320,6 +334,11 @@ int kgsl_sync_timeline_create(struct kgsl_context *context)
 	INIT_LIST_HEAD(&ktimeline->child_list_head);
 	spin_lock_init(&ktimeline->lock);
 	ktimeline->device = context->device;
+
+	/*
+	 * The context pointer is valid till detach time, where we put the
+	 * refcount on the context
+	 */
 	ktimeline->context = context;
 
 	context->ktimeline = ktimeline;
@@ -352,27 +371,30 @@ static void kgsl_sync_timeline_signal(struct kgsl_sync_timeline *ktimeline,
 	kgsl_sync_timeline_put(ktimeline);
 }
 
-void kgsl_sync_timeline_destroy(struct kgsl_context *context)
+void kgsl_sync_timeline_detach(struct kgsl_sync_timeline *ktimeline)
 {
-	kfree(context->ktimeline);
+	unsigned long flags;
+	struct kgsl_context *context = ktimeline->context;
+
+	/* Set context pointer to NULL and drop our refcount on the context */
+	spin_lock_irqsave(&ktimeline->lock, flags);
+	ktimeline->context = NULL;
+	spin_unlock_irqrestore(&ktimeline->lock, flags);
+	kgsl_context_put(context);
 }
 
-static void kgsl_sync_timeline_release(struct kref *kref)
+static void kgsl_sync_timeline_destroy(struct kref *kref)
 {
 	struct kgsl_sync_timeline *ktimeline =
 		container_of(kref, struct kgsl_sync_timeline, kref);
 
-	/*
-	 * Only put the context refcount here. The context destroy function
-	 * will call kgsl_sync_timeline_destroy() to kfree it
-	 */
-	kgsl_context_put(ktimeline->context);
+	kfree(ktimeline);
 }
 
 void kgsl_sync_timeline_put(struct kgsl_sync_timeline *ktimeline)
 {
 	if (ktimeline)
-		kref_put(&ktimeline->kref, kgsl_sync_timeline_release);
+		kref_put(&ktimeline->kref, kgsl_sync_timeline_destroy);
 }
 
 static const struct dma_fence_ops kgsl_sync_fence_ops = {

drivers/gpu/msm/kgsl_sync.h

@@ -1,6 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 /*
- * Copyright (c) 2012-2014,2018-2019 The Linux Foundation. All rights reserved.
+ * Copyright (c) 2012-2014,2018-2019, 2021, The Linux Foundation. All rights reserved.
  */
 #ifndef __KGSL_SYNC_H
 #define __KGSL_SYNC_H
@@ -9,7 +9,8 @@
 
 /**
  * struct kgsl_sync_timeline - A sync timeline associated with a kgsl context
- * @kref: Refcount to keep the struct alive until all its fences are released
+ * @kref: Refcount to keep the struct alive until all its fences are signaled,
+	  and as long as the context exists
  * @name: String to describe this timeline
  * @fence_context: Used by the fence driver to identify fences belonging to
  *		   this context
@@ -80,7 +81,7 @@ int kgsl_add_fence_event(struct kgsl_device *device,
 
 int kgsl_sync_timeline_create(struct kgsl_context *context);
 
-void kgsl_sync_timeline_destroy(struct kgsl_context *context);
+void kgsl_sync_timeline_detach(struct kgsl_sync_timeline *ktimeline);
 
 void kgsl_sync_timeline_put(struct kgsl_sync_timeline *ktimeline);
 
@@ -118,7 +119,7 @@ static inline int kgsl_sync_timeline_create(struct kgsl_context *context)
 	return 0;
 }
 
-static inline void kgsl_sync_timeline_destroy(struct kgsl_context *context)
+static inline void kgsl_sync_timeline_detach(struct kgsl_sync_timeline *ktimeline)
 {
 }