cgroups: fix lockdep subclasses overflow

[deliverable/linux.git] / include / linux / cgroup.h

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 08b78c09b09a111867b68b443225f53ece341093..499900d0cee7110748229ee3898b50734352e5e4 100644 (file)
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -52,9 +52,9 @@ struct cgroup_subsys_state {
         * hierarchy structure */
        struct cgroup *cgroup;
 
-       /* State maintained by the cgroup system to allow
-        * subsystems to be "busy". Should be accessed via css_get()
-        * and css_put() */
+       /* State maintained by the cgroup system to allow subsystems
+        * to be "busy". Should be accessed via css_get(),
+        * css_tryget() and and css_put(). */
 
        atomic_t refcnt;
 
@@ -64,11 +64,14 @@ struct cgroup_subsys_state {
 /* bits in struct cgroup_subsys_state flags field */
 enum {
        CSS_ROOT, /* This CSS is the root of the subsystem */
+       CSS_REMOVED, /* This CSS is dead */
 };
 
 /*
- * Call css_get() to hold a reference on the cgroup;
- *
+ * Call css_get() to hold a reference on the css; it can be used
+ * for a reference obtained via:
+ * - an existing ref-counted reference to the css
+ * - task->cgroups for a locked task
  */
 
 static inline void css_get(struct cgroup_subsys_state *css)
@@ -77,9 +80,33 @@ static inline void css_get(struct cgroup_subsys_state *css)
        if (!test_bit(CSS_ROOT, &css->flags))
                atomic_inc(&css->refcnt);
 }
+
+static inline bool css_is_removed(struct cgroup_subsys_state *css)
+{
+       return test_bit(CSS_REMOVED, &css->flags);
+}
+
+/*
+ * Call css_tryget() to take a reference on a css if your existing
+ * (known-valid) reference isn't already ref-counted. Returns false if
+ * the css has been destroyed.
+ */
+
+static inline bool css_tryget(struct cgroup_subsys_state *css)
+{
+       if (test_bit(CSS_ROOT, &css->flags))
+               return true;
+       while (!atomic_inc_not_zero(&css->refcnt)) {
+               if (test_bit(CSS_REMOVED, &css->flags))
+                       return false;
+               cpu_relax();
+       }
+       return true;
+}
+
 /*
  * css_put() should be called to release a reference taken by
- * css_get()
+ * css_get() or css_tryget()
  */
 
 extern void __css_put(struct cgroup_subsys_state *css);
@@ -116,7 +143,7 @@ struct cgroup {
        struct list_head children;      /* my children */
 
        struct cgroup *parent;  /* my parent */
-       struct dentry *dentry;          /* cgroup fs entry */
+       struct dentry *dentry;          /* cgroup fs entry, RCU protected */
 
        /* Private pointers for each registered subsystem */
        struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
@@ -145,6 +172,9 @@ struct cgroup {
        int pids_use_count;
        /* Length of the current tasks_pids array */
        int pids_length;
+
+       /* For RCU-protected deletion */
+       struct rcu_head rcu_head;
 };
 
 /* A css_set is a structure holding pointers to a set of
@@ -337,9 +367,24 @@ struct cgroup_subsys {
 #define MAX_CGROUP_TYPE_NAMELEN 32
        const char *name;
 
-       /* Protected by RCU */
-       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;
+       struct lock_class_key subsys_key;
 
+       /*
+        * 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;
 };