[PATCH RFC v2 4/7] drm: Add helper to obtain cgroup of drm_file's owning process

[Matt Roper <matthew.d.roper@xxxxxxxxx>]

Signed-off-by: Matt Roper <matthew.d.roper@xxxxxxxxx>
---
 include/drm/drm_file.h        | 20 ++++++++++++++++++++
 kernel/cgroup/cgroup_driver.c | 12 ++++++++++--
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
index 0e0c868451a5..72ac40530ad3 100644
--- a/include/drm/drm_file.h
+++ b/include/drm/drm_file.h
@@ -32,6 +32,7 @@
 
 #include <linux/types.h>
 #include <linux/completion.h>
+#include <linux/cgroup.h>
 
 #include <uapi/drm/drm.h>
 
@@ -378,4 +379,23 @@ void drm_event_cancel_free(struct drm_device *dev,
 void drm_send_event_locked(struct drm_device *dev, struct drm_pending_event *e);
 void drm_send_event(struct drm_device *dev, struct drm_pending_event *e);
 
+#ifdef CONFIG_CGROUPS
+/**
+ * drm_file_get_cgroup - obtain cgroup for drm_file's owning process
+ * @file_priv: DRM file
+ *
+ * Obtains the cgroup from a specific hierarchy that the drm_file's owning
+ * process belongs to.  The cgroup may be used to set driver-specific
+ * policy (priority, vram usage, etc.).
+ */
+static inline struct cgroup *
+drm_file_get_cgroup(struct drm_file *file_priv)
+{
+	return cgroup_for_driver_process(file_priv->pid);
+}
+#else
+static inline struct cgroup *
+drm_file_get_cgroup(struct drm_file *file_priv) { return NULL; }
+#endif
+
 #endif /* _DRM_FILE_H_ */
diff --git a/kernel/cgroup/cgroup_driver.c b/kernel/cgroup/cgroup_driver.c
index 4f870cbb9212..db0e268b9546 100644
--- a/kernel/cgroup/cgroup_driver.c
+++ b/kernel/cgroup/cgroup_driver.c
@@ -4,6 +4,7 @@
 
 #include <linux/hashtable.h>
 #include <linux/mm.h>
+#include <linux/sched/task.h>
 
 /*
  * General data structure returned by cgroup_driver_init() and used as a
@@ -143,12 +144,19 @@ EXPORT_SYMBOL(cgroup_driver_get_data);
 struct cgroup *
 cgroup_for_driver_process(struct pid *pid)
 {
-	struct task_struct *task = pid_task(pid, PIDTYPE_PID);
+	struct task_struct *task;
+	struct cgroup *cgrp;
+
+	read_lock(&tasklist_lock);
+	task = pid_task(pid, PIDTYPE_PID);
+	read_unlock(&tasklist_lock);
 
 	mutex_lock(&cgroup_mutex);
 	spin_lock_irq(&css_set_lock);
-	task_cgroup_from_root(task, &cgrp_dfl_root);
+	cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
 	spin_unlock_irq(&css_set_lock);
 	mutex_unlock(&cgroup_mutex);
+
+	return cgrp;
 }
 EXPORT_SYMBOL(cgroup_for_driver_process);
-- 
2.14.3

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