cgroup: add tracepoints for basic operations

Debugging what goes wrong with cgroup setup can get hairy.  Add
tracepoints for cgroup hierarchy mount, cgroup creation/destruction
and task migration operations for better visibility.

Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/cgroup.c

@@ -64,6 +64,9 @@
 #include <linux/file.h>
 #include <net/sock.h>
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/cgroup.h>
+
 /*
  * pidlists linger the following amount before being destroyed.  The goal
  * is avoiding frequent destruction in the middle of consecutive read calls
@@ -1176,6 +1179,8 @@ static void cgroup_destroy_root(struct cgroup_root *root)
 	struct cgroup *cgrp = &root->cgrp;
 	struct cgrp_cset_link *link, *tmp_link;
 
+	trace_cgroup_destroy_root(root);
+
 	cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
 
 	BUG_ON(atomic_read(&root->nr_cgrps));
@@ -1874,6 +1879,9 @@ static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
 		strcpy(root->release_agent_path, opts.release_agent);
 		spin_unlock(&release_agent_path_lock);
 	}
+
+	trace_cgroup_remount(root);
+
  out_unlock:
 	kfree(opts.release_agent);
 	kfree(opts.name);
@@ -2031,6 +2039,8 @@ static int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
 	if (ret)
 		goto destroy_root;
 
+	trace_cgroup_setup_root(root);
+
 	/*
 	 * There must be no failure case after here, since rebinding takes
 	 * care of subsystems' refcounts, which are explicitly dropped in
@@ -2825,6 +2835,10 @@ static int cgroup_attach_task(struct cgroup *dst_cgrp,
 		ret = cgroup_migrate(leader, threadgroup, dst_cgrp->root);
 
 	cgroup_migrate_finish(&preloaded_csets);
+
+	if (!ret)
+		trace_cgroup_attach_task(dst_cgrp, leader, threadgroup);
+
 	return ret;
 }
 
@@ -3587,6 +3601,8 @@ static int cgroup_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
 	mutex_lock(&cgroup_mutex);
 
 	ret = kernfs_rename(kn, new_parent, new_name_str);
+	if (!ret)
+		trace_cgroup_rename(cgrp);
 
 	mutex_unlock(&cgroup_mutex);
 
@@ -4355,6 +4371,8 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
 
 		if (task) {
 			ret = cgroup_migrate(task, false, to->root);
+			if (!ret)
+				trace_cgroup_transfer_tasks(to, task, false);
 			put_task_struct(task);
 		}
 	} while (task && !ret);
@@ -5020,6 +5038,8 @@ static void css_release_work_fn(struct work_struct *work)
 			ss->css_released(css);
 	} else {
 		/* cgroup release path */
+		trace_cgroup_release(cgrp);
+
 		cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
 		cgrp->id = -1;
 
@@ -5306,6 +5326,8 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
 	if (ret)
 		goto out_destroy;
 
+	trace_cgroup_mkdir(cgrp);
+
 	/* let's create and online css's */
 	kernfs_activate(kn);
 
@@ -5481,6 +5503,9 @@ static int cgroup_rmdir(struct kernfs_node *kn)
 
 	ret = cgroup_destroy_locked(cgrp);
 
+	if (!ret)
+		trace_cgroup_rmdir(cgrp);
+
 	cgroup_kn_unlock(kn);
 	return ret;
 }