drm/i915: Track all user contexts per client

We soon want to start answering questions like how much GPU time is the
context belonging to a client which exited still using.

To enable this we start tracking all context belonging to a client on a
separate list.
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Aravind Iddamsetty <aravind.iddamsetty@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220401142205.3123159-5-tvrtko.ursulin@linux.intel.com

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

@@ -1490,6 +1490,8 @@ static void set_closed_name(struct i915_gem_context *ctx)
 
 static void context_close(struct i915_gem_context *ctx)
 {
+	struct i915_drm_client *client;
+
 	/* Flush any concurrent set_engines() */
 	mutex_lock(&ctx->engines_mutex);
 	unpin_engines(__context_engines_static(ctx));
@@ -1514,6 +1516,13 @@ static void context_close(struct i915_gem_context *ctx)
 	list_del(&ctx->link);
 	spin_unlock(&ctx->i915->gem.contexts.lock);
 
+	client = ctx->client;
+	if (client) {
+		spin_lock(&client->ctx_lock);
+		list_del_rcu(&ctx->client_link);
+		spin_unlock(&client->ctx_lock);
+	}
+
 	mutex_unlock(&ctx->mutex);
 
 	/*
@@ -1695,6 +1704,10 @@ static void gem_context_register(struct i915_gem_context *ctx,
 	old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL);
 	WARN_ON(old);
 
+	spin_lock(&ctx->client->ctx_lock);
+	list_add_tail_rcu(&ctx->client_link, &ctx->client->ctx_list);
+	spin_unlock(&ctx->client->ctx_lock);
+
 	spin_lock(&i915->gem.contexts.lock);
 	list_add_tail(&ctx->link, &i915->gem.contexts.list);
 	spin_unlock(&i915->gem.contexts.lock);

drivers/gpu/drm/i915/gem/i915_gem_context_types.h

@@ -296,6 +296,9 @@ struct i915_gem_context {
 	/** @client: struct i915_drm_client */
 	struct i915_drm_client *client;
 
+	/** link: &drm_client.context_list */
+	struct list_head client_link;
+
 	/**
 	 * @ref: reference count
 	 *

drivers/gpu/drm/i915/i915_drm_client.c

@@ -38,6 +38,8 @@ struct i915_drm_client *i915_drm_client_add(struct i915_drm_clients *clients)
 		goto err;
 
 	kref_init(&client->kref);
+	spin_lock_init(&client->ctx_lock);
+	INIT_LIST_HEAD(&client->ctx_list);
 	client->clients = clients;
 
 	return client;

drivers/gpu/drm/i915/i915_drm_client.h

@@ -7,6 +7,8 @@
 #define __I915_DRM_CLIENT_H__
 
 #include <linux/kref.h>
+#include <linux/list.h>
+#include <linux/spinlock.h>
 #include <linux/xarray.h>
 
 #include "gt/intel_engine_types.h"
@@ -27,6 +29,9 @@ struct i915_drm_client {
 
 	unsigned int id;
 
+	spinlock_t ctx_lock; /* For add/remove from ctx_list. */
+	struct list_head ctx_list; /* List of contexts belonging to client. */
+
 	struct i915_drm_clients *clients;
 
 	/**