cgroup: introduce cancel_attach()

Add cancel_attach() operation to struct cgroup_subsys.  cancel_attach()
can be used when can_attach() operation prepares something for the subsys,
but we should rollback what can_attach() operation has prepared if attach
task fails after we've succeeded in can_attach().

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Reviewed-by: Paul Menage <menage@google.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 33 insertions, 7 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 4fd90e129772..be45d2f6008a 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1554,7 +1554,7 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
 int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
 {
         int retval = 0;
-        struct cgroup_subsys *ss;
+        struct cgroup_subsys *ss, *failed_ss = NULL;
         struct cgroup *oldcgrp;
         struct css_set *cg;
         struct css_set *newcg;
@@ -1568,8 +1568,16 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
         for_each_subsys(root, ss) {
                 if (ss->can_attach) {
                         retval = ss->can_attach(ss, cgrp, tsk, false);
-                        if (retval)
-                                return retval;
+                        if (retval) {
+                                /*
+                                 * Remember on which subsystem the can_attach()
+                                 * failed, so that we only call cancel_attach()
+                                 * against the subsystems whose can_attach()
+                                 * succeeded. (See below)
+                                 */
+                                failed_ss = ss;
+                                goto out;
+                        }
                 }
         }
 
@@ -1583,14 +1591,17 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
          */
         newcg = find_css_set(cg, cgrp);
         put_css_set(cg);
-        if (!newcg)
-                return -ENOMEM;
+        if (!newcg) {
+                retval = -ENOMEM;
+                goto out;
+        }
 
         task_lock(tsk);
         if (tsk->flags & PF_EXITING) {
                 task_unlock(tsk);
                 put_css_set(newcg);
-                return -ESRCH;
+                retval = -ESRCH;
+                goto out;
         }
         rcu_assign_pointer(tsk->cgroups, newcg);
         task_unlock(tsk);
@@ -1616,7 +1627,22 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
          * is no longer empty.
          */
         cgroup_wakeup_rmdir_waiter(cgrp);
-        return 0;
+out:
+        if (retval) {
+                for_each_subsys(root, ss) {
+                        if (ss == failed_ss)
+                                /*
+                                 * This subsystem was the one that failed the
+                                 * can_attach() check earlier, so we don't need
+                                 * to call cancel_attach() against it or any
+                                 * remaining subsystems.
+                                 */
+                                break;
+                        if (ss->cancel_attach)
+                                ss->cancel_attach(ss, cgrp, tsk, false);
+                }
+        }
+        return retval;
 }
 
 /*