1 files changed, 34 insertions, 9 deletions

diff --git a/include/linux/nsproxy.h b/include/linux/nsproxy.h
index f1eca68751a9..0e66b57631fc 100644
--- a/include/linux/nsproxy.h
+++ b/include/linux/nsproxy.h
@@ -32,8 +32,39 @@ struct nsproxy {
 };
 extern struct nsproxy init_nsproxy;
 
+/*
+ * the namespaces access rules are:
+ *
+ *  1. only current task is allowed to change tsk->nsproxy pointer or
+ *     any pointer on the nsproxy itself
+ *
+ *  2. when accessing (i.e. reading) current task's namespaces - no
+ *     precautions should be taken - just dereference the pointers
+ *
+ *  3. the access to other task namespaces is performed like this
+ *     rcu_read_lock();
+ *     nsproxy = task_nsproxy(tsk);
+ *     if (nsproxy != NULL) {
+ *             / *
+ *               * work with the namespaces here
+ *               * e.g. get the reference on one of them
+ *               * /
+ *     } / *
+ *         * NULL task_nsproxy() means that this task is
+ *         * almost dead (zombie)
+ *         * /
+ *     rcu_read_unlock();
+ *
+ */
+
+static inline struct nsproxy *task_nsproxy(struct task_struct *tsk)
+{
+        return rcu_dereference(tsk->nsproxy);
+}
+
 int copy_namespaces(unsigned long flags, struct task_struct *tsk);
-void get_task_namespaces(struct task_struct *tsk);
+void exit_task_namespaces(struct task_struct *tsk);
+void switch_task_namespaces(struct task_struct *tsk, struct nsproxy *new);
 void free_nsproxy(struct nsproxy *ns);
 int unshare_nsproxy_namespaces(unsigned long, struct nsproxy **,
         struct fs_struct *);
@@ -45,15 +76,9 @@ static inline void put_nsproxy(struct nsproxy *ns)
         }
 }
 
-static inline void exit_task_namespaces(struct task_struct *p)
+static inline void get_nsproxy(struct nsproxy *ns)
 {
-        struct nsproxy *ns = p->nsproxy;
-        if (ns) {
-                task_lock(p);
-                p->nsproxy = NULL;
-                task_unlock(p);
-                put_nsproxy(ns);
-        }
+        atomic_inc(&ns->count);
 }
 
 #ifdef CONFIG_CGROUP_NS