[PATCH 4/8] cgroups: New cancel_attach_task subsystem callback

[Frederic Weisbecker <fweisbec@gmail.com>]

To cancel a process attachment on a subsystem, we only call the
cancel_attach() callback once on the leader but we have no
way to cancel the attachment individually for each member of
the process group.

This is going to be needed for the max number of tasks susbystem
that is coming.

To prepare for this integration, call a new cancel_attach_task()
callback on each task of the group until we reach the member that
failed to attach.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Paul Menage <menage@google.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Aditya Kali <adityakali@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
---
 include/linux/cgroup.h |    1 +
 kernel/cgroup.c        |   15 ++++++++++++---
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index e8288a0..94454143 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -472,6 +472,7 @@ struct cgroup_subsys {
 			       struct task_struct *tsk);
 	void (*cancel_attach)(struct cgroup_subsys *ss, struct cgroup *cgrp,
 			      struct task_struct *tsk);
+	void (*cancel_attach_task)(struct cgroup *cgrp, struct task_struct *tsk);
 	void (*pre_attach)(struct cgroup *cgrp);
 	void (*attach_task)(struct cgroup *cgrp, struct cgroup *old_cgrp, struct task_struct *tsk);
 	void (*attach)(struct cgroup_subsys *ss, struct cgroup *cgrp,
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index c3ee4cf..210dc05 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1989,7 +1989,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
 {
 	int retval, i, group_size;
 	struct cgroup_subsys *ss, *failed_ss = NULL;
-	bool cancel_failed_ss = false;
+	struct task_struct *failed_task = NULL;
 	/* guaranteed to be initialized later, but the compiler needs this */
 	struct cgroup *oldcgrp = NULL;
 	struct css_set *oldcg;
@@ -2077,7 +2077,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
 				retval = ss->can_attach_task(cgrp, oldcgrp, tsk);
 				if (retval) {
 					failed_ss = ss;
-					cancel_failed_ss = true;
+					failed_task = tsk;
 					goto out_cancel_attach;
 				}
 			}
@@ -2172,8 +2172,17 @@ out_cancel_attach:
 	/* same deal as in cgroup_attach_task */
 	if (retval) {
 		for_each_subsys(root, ss) {
+			if (ss->cancel_attach_task && (ss != failed_ss || failed_task)) {
+				for (i = 0; i < group_size; i++) {
+					tsk = flex_array_get_ptr(group, i);
+					if (tsk == failed_task)
+						break;
+					ss->cancel_attach_task(cgrp, tsk);
+				}
+			}
+
 			if (ss == failed_ss) {
-				if (cancel_failed_ss && ss->cancel_attach)
+				if (failed_task && ss->cancel_attach)
 					ss->cancel_attach(ss, cgrp, leader);
 				break;
 			}
-- 
1.7.5.4