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-rw-r--r--include/linux/cgroup.h17
1 files changed, 16 insertions, 1 deletions
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 73d1c730c3c..ce1c1f34c30 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -340,8 +340,23 @@ struct cgroup_subsys {
#define MAX_CGROUP_TYPE_NAMELEN 32
const char *name;
- struct cgroupfs_root *root;
+ /*
+ * Protects sibling/children links of cgroups in this
+ * hierarchy, plus protects which hierarchy (or none) the
+ * subsystem is a part of (i.e. root/sibling). To avoid
+ * potential deadlocks, the following operations should not be
+ * undertaken while holding any hierarchy_mutex:
+ *
+ * - allocating memory
+ * - initiating hotplug events
+ */
+ struct mutex hierarchy_mutex;
+ /*
+ * Link to parent, and list entry in parent's children.
+ * Protected by this->hierarchy_mutex and cgroup_lock()
+ */
+ struct cgroupfs_root *root;
struct list_head sibling;
};