[RFC 09/12] cgroup/drm: Client exit hook

[Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>]

From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

We need the ability for DRM core to inform the cgroup controller when a
client has closed a DRM file descriptor. This will allow us not needing
to keep state relating to GPU time usage by tasks sets in the cgroup
controller itself.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
 drivers/gpu/drm/drm_cgroup.c |  9 +++++++++
 include/linux/cgroup_drm.h   |  4 ++++
 kernel/cgroup/drm.c          | 13 +++++++++++++
 3 files changed, 26 insertions(+)

diff --git a/drivers/gpu/drm/drm_cgroup.c b/drivers/gpu/drm/drm_cgroup.c
index 09249f795af3..ea1479d05355 100644
--- a/drivers/gpu/drm/drm_cgroup.c
+++ b/drivers/gpu/drm/drm_cgroup.c
@@ -3,6 +3,8 @@
  * Copyright © 2022 Intel Corporation
  */
 
+#include <linux/cgroup_drm.h>
+
 #include <drm/drm_drv.h>
 #include <drm/drm_clients.h>
 #include <drm/drm_print.h>
@@ -32,6 +34,7 @@ void drm_clients_close(struct drm_file *file_priv)
 {
 	struct drm_device *dev = file_priv->minor->dev;
 	struct drm_pid_clients *clients;
+	struct task_struct *task;
 	struct pid *pid;
 
 	lockdep_assert_held(&dev->filelist_mutex);
@@ -44,6 +47,12 @@ void drm_clients_close(struct drm_file *file_priv)
 	if (drm_WARN_ON_ONCE(dev, !clients))
 		return;
 
+	task = get_pid_task(pid, PIDTYPE_PID);
+	if (task) {
+		drmcgroup_client_exited(task);
+		put_task_struct(task);
+	}
+
 	__del_clients(clients, file_priv, (unsigned long)pid);
 }
 
diff --git a/include/linux/cgroup_drm.h b/include/linux/cgroup_drm.h
index bf8abc6b8ebf..2f755b896136 100644
--- a/include/linux/cgroup_drm.h
+++ b/include/linux/cgroup_drm.h
@@ -6,4 +6,8 @@
 #ifndef _CGROUP_DRM_H
 #define _CGROUP_DRM_H
 
+struct task_struct;
+
+void drmcgroup_client_exited(struct task_struct *task);
+
 #endif	/* _CGROUP_DRM_H */
diff --git a/kernel/cgroup/drm.c b/kernel/cgroup/drm.c
index 48a8d646a094..3e7f165806de 100644
--- a/kernel/cgroup/drm.c
+++ b/kernel/cgroup/drm.c
@@ -22,6 +22,11 @@ css_to_drmcs(struct cgroup_subsys_state *css)
 	return container_of(css, struct drm_cgroup_state, css);
 }
 
+static inline struct drm_cgroup_state *get_task_drmcs(struct task_struct *task)
+{
+	return css_to_drmcs(task_get_css(task, drm_cgrp_id));
+}
+
 static struct drm_root_cgroup_state root_drmcs;
 
 static void drmcs_free(struct cgroup_subsys_state *css)
@@ -46,6 +51,14 @@ drmcs_alloc(struct cgroup_subsys_state *parent_css)
 	return &drmcs->css;
 }
 
+void drmcgroup_client_exited(struct task_struct *task)
+{
+	struct drm_cgroup_state *drmcs = get_task_drmcs(task);
+
+	css_put(&drmcs->css);
+}
+EXPORT_SYMBOL_GPL(drmcgroup_client_exited);
+
 struct cftype files[] = {
 	{ } /* Zero entry terminates. */
 };
-- 
2.34.1