[PATCH RFC v2 3/7] cgroup: Add interface to allow drivers to lookup process cgroup membership

[Matt Roper <matthew.d.roper@intel.com>]

Drivers will need to save/restore the appropriate cgroup data for the process
submitting a driver request.  Add an interface for drivers to determine the
cgroup for the userspace process submitting a driver request.

Cc: Tejun Heo <tj@kernel.org>
Cc: cgroups@vger.kernel.org
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
---
 include/linux/cgroup.h        |  6 ++++++
 kernel/cgroup/cgroup_driver.c | 24 ++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 0ba1374122c7..05ebfb97bcde 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -842,6 +842,7 @@ void cgroup_driver_release(struct cgroup_driver *drv);
 struct cgroup_driver_data * cgroup_driver_get_data(struct cgroup_driver *drv,
 						   struct cgroup *cgrp,
 						   bool *is_new);
+struct cgroup *cgroup_for_driver_process(struct pid *pid);
 
 #else /* !CONFIG_CGROUP_DRIVER */
 
@@ -857,6 +858,11 @@ cgroup_driver_get_data(struct cgroup_driver *drv,
 {
 	return ERR_PTR(-EINVAL);
 }
+static inline struct cgroup *
+cgroup_for_driver_process(struct pid *pid)
+{
+	return NULL;
+}
 
 #endif /* !CONFIG_CGROUP_DRIVER */
 
diff --git a/kernel/cgroup/cgroup_driver.c b/kernel/cgroup/cgroup_driver.c
index 0d893395dc7b..4f870cbb9212 100644
--- a/kernel/cgroup/cgroup_driver.c
+++ b/kernel/cgroup/cgroup_driver.c
@@ -128,3 +128,27 @@ cgroup_driver_get_data(struct cgroup_driver *drv,
 	return data;
 }
 EXPORT_SYMBOL(cgroup_driver_get_data);
+
+/**
+ * cgroup_for_driver_process - return the cgroup for a process
+ * @pid: process to lookup cgroup for
+ *
+ * Returns the cgroup from the v2 hierarchy that a process belongs to.
+ * This function is intended to be called from drivers and will obtain
+ * the necessary cgroup locks.
+ *
+ * RETURNS:
+ * Process' cgroup in the default (v2) hierarchy
+ */
+struct cgroup *
+cgroup_for_driver_process(struct pid *pid)
+{
+	struct task_struct *task = pid_task(pid, PIDTYPE_PID);
+
+	mutex_lock(&cgroup_mutex);
+	spin_lock_irq(&css_set_lock);
+	task_cgroup_from_root(task, &cgrp_dfl_root);
+	spin_unlock_irq(&css_set_lock);
+	mutex_unlock(&cgroup_mutex);
+}
+EXPORT_SYMBOL(cgroup_for_driver_process);
-- 
2.14.3

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