Extend walk_tg_tree to accept a positional argument

static int walk_tg_tree_from(struct task_group *from,
			     tg_visitor down, tg_visitor up, void *data)

Existing semantics are preserved, caller must hold rcu_lock() or sufficient
analogue.

Signed-off-by: Paul Turner <pjt@google.com>
---
 kernel/sched.c |   34 +++++++++++++++++++++++-----------
 1 file changed, 23 insertions(+), 11 deletions(-)

Index: tip/kernel/sched.c
===================================================================
--- tip.orig/kernel/sched.c
+++ tip/kernel/sched.c
@@ -1430,21 +1430,19 @@ static inline void dec_cpu_load(struct r
 #if (defined(CONFIG_SMP) && defined(CONFIG_FAIR_GROUP_SCHED)) || defined(CONFIG_RT_GROUP_SCHED)
 typedef int (*tg_visitor)(struct task_group *, void *);
 
-/*
- * Iterate the full tree, calling @down when first entering a node and @up when
- * leaving it for the final time.
- */
-static int walk_tg_tree(tg_visitor down, tg_visitor up, void *data)
+/* Iterate task_group tree rooted at *from */
+static int walk_tg_tree_from(struct task_group *from,
+			     tg_visitor down, tg_visitor up, void *data)
 {
 	struct task_group *parent, *child;
 	int ret;
 
-	rcu_read_lock();
-	parent = &root_task_group;
+	parent = from;
+
 down:
 	ret = (*down)(parent, data);
 	if (ret)
-		goto out_unlock;
+		goto out;
 	list_for_each_entry_rcu(child, &parent->children, siblings) {
 		parent = child;
 		goto down;
@@ -1453,14 +1451,28 @@ up:
 		continue;
 	}
 	ret = (*up)(parent, data);
-	if (ret)
-		goto out_unlock;
+	if (ret || parent == from)
+		goto out;
 
 	child = parent;
 	parent = parent->parent;
 	if (parent)
 		goto up;
-out_unlock:
+out:
+	return ret;
+}
+
+/*
+ * Iterate the full tree, calling @down when first entering a node and @up when
+ * leaving it for the final time.
+ */
+
+static inline int walk_tg_tree(tg_visitor down, tg_visitor up, void *data)
+{
+	int ret;
+
+	rcu_read_lock();
+	ret = walk_tg_tree_from(&root_task_group, down, up, data);
 	rcu_read_unlock();
 
 	return ret;


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