[PATCH RFC 1/4] cgroup, perf: Add ability to connect to perf cgroup from other cgroup controller

[Kenny Ho <Kenny.Ho@xxxxxxx>]

This provides the ability to allocate cgroup specific perf_event by
bpf-cgroup in later patch

Change-Id: I13aa7f3dfc2883ba3663c0b94744a6169504bbd8
Signed-off-by: Kenny Ho <Kenny.Ho@xxxxxxx>
---
 include/linux/cgroup.h     |  2 ++
 include/linux/perf_event.h |  2 ++
 kernel/cgroup/cgroup.c     |  4 ++--
 kernel/events/core.c       | 17 +++++++++++++++++
 4 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 75c151413fda..1754e33cfe5e 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -97,6 +97,8 @@ extern struct css_set init_css_set;
 
 bool css_has_online_children(struct cgroup_subsys_state *css);
 struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss);
+struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgroup,
+					      struct cgroup_subsys *ss);
 struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgroup,
 					 struct cgroup_subsys *ss);
 struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgroup,
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 0cbc5dfe1110..9c440db65c18 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -926,6 +926,8 @@ struct perf_cgroup {
 	struct perf_cgroup_info	__percpu *info;
 };
 
+extern struct perf_cgroup *cgroup_tryget_perf_cgroup(struct cgroup *cgrp);
+
 /*
  * Must ensure cgroup is pinned (css_get) before calling
  * this function. In other words, we cannot call this function
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 570b0c97392a..a645b212b69b 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -495,8 +495,8 @@ static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
  * Find and get @cgrp's css associated with @ss.  If the css doesn't exist
  * or is offline, %NULL is returned.
  */
-static struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgrp,
-						     struct cgroup_subsys *ss)
+struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgrp,
+					      struct cgroup_subsys *ss)
 {
 	struct cgroup_subsys_state *css;
 
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 20367196fa9a..d34e00749c9b 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -941,6 +941,18 @@ static int perf_cgroup_ensure_storage(struct perf_event *event,
 	return ret;
 }
 
+struct perf_cgroup *cgroup_tryget_perf_cgroup(struct cgroup *cgrp)
+{
+	struct cgroup_subsys_state *css;
+
+	css = cgroup_tryget_css(cgrp, &perf_event_cgrp_subsys);
+
+	if (!css)
+		return NULL;
+
+	return container_of(css, struct perf_cgroup, css);
+}
+
 static inline int perf_cgroup_connect(int fd, struct perf_event *event,
 				      struct perf_event_attr *attr,
 				      struct perf_event *group_leader)
@@ -1080,6 +1092,11 @@ static inline void perf_cgroup_sched_in(struct task_struct *prev,
 {
 }
 
+struct perf_cgroup *cgroup_tryget_perf_cgroup(struct cgroup *cgrp)
+{
+	return NULL;
+}
+
 static inline int perf_cgroup_connect(pid_t pid, struct perf_event *event,
 				      struct perf_event_attr *attr,
 				      struct perf_event *group_leader)
-- 
2.25.1