My main purpose of this patch is for memory controller..

This patch adds a handler "pre_destroy" to cgroup_subsys.
It is called before cgroup_rmdir() checks all subsys's refcnt.

I think this is useful for subsyses which have some extra refs
even if there are no tasks in cgroup.

Signed-off-by: KAMEZAWA Hiroyuki <[EMAIL PROTECTED]>

 include/linux/cgroup.h |    1 +
 kernel/cgroup.c        |    7 +++++++
 2 files changed, 8 insertions(+)

Index: devel-2.6.23-mm1/include/linux/cgroup.h
===================================================================
--- devel-2.6.23-mm1.orig/include/linux/cgroup.h
+++ devel-2.6.23-mm1/include/linux/cgroup.h
@@ -233,6 +233,7 @@ int cgroup_is_descendant(const struct cg
 struct cgroup_subsys {
        struct cgroup_subsys_state *(*create)(struct cgroup_subsys *ss,
                                                  struct cgroup *cont);
+       void (*pre_destroy)(struct cgroup_subsys *ss, struct cgroup *cont);
        void (*destroy)(struct cgroup_subsys *ss, struct cgroup *cont);
        int (*can_attach)(struct cgroup_subsys *ss,
                          struct cgroup *cont, struct task_struct *tsk);
Index: devel-2.6.23-mm1/kernel/cgroup.c
===================================================================
--- devel-2.6.23-mm1.orig/kernel/cgroup.c
+++ devel-2.6.23-mm1/kernel/cgroup.c
@@ -2158,6 +2158,13 @@ static int cgroup_rmdir(struct inode *un
        parent = cont->parent;
        root = cont->root;
        sb = root->sb;
+       /*
+        * Notify subsyses that rmdir() request comes.
+        */
+       for_each_subsys(root, ss) {
+               if ((cont->subsys[ss->subsys_id]) && ss->pre_destroy)
+                       ss->pre_destroy(ss, cont);
+       }
 
        if (cgroup_has_css_refs(cont)) {
                mutex_unlock(&cgroup_mutex);

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