[RFC PATCH 12/12] cgroups: Convert task counter to use the subsys fork callback

[Frederic Weisbecker <fweisbec@gmail.com>]

Instead of using an ad hoc hook on the fork path for the task
counter, use the subsystem fork callback that we can now use
to cancel the fork.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Menage <paul@paulmenage.org>
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>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Tim Hockin <thockin@hockin.org>
Cc: Tejun Heo <tj@kernel.org>
---
 include/linux/cgroup.h       |    9 ---------
 kernel/cgroup_task_counter.c |    3 ++-
 kernel/fork.c                |    4 ----
 3 files changed, 2 insertions(+), 14 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 253543b..7ba9a38 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -663,13 +663,4 @@ static inline int cgroup_attach_task_current_cg(struct task_struct *t)
 
 #endif /* !CONFIG_CGROUPS */
 
-#ifdef CONFIG_CGROUP_TASK_COUNTER
-int cgroup_task_counter_fork(struct task_struct *child);
-#else
-static inline int cgroup_task_counter_fork(struct task_struct *child)
-{
-	return 0;
-}
-#endif /* CONFIG_CGROUP_TASK_COUNTER */
-
 #endif /* _LINUX_CGROUP_H */
diff --git a/kernel/cgroup_task_counter.c b/kernel/cgroup_task_counter.c
index 2ca7f41..dbdb625 100644
--- a/kernel/cgroup_task_counter.c
+++ b/kernel/cgroup_task_counter.c
@@ -168,7 +168,7 @@ static int task_counter_populate(struct cgroup_subsys *ss, struct cgroup *cgrp)
 	return cgroup_add_files(cgrp, ss, files, ARRAY_SIZE(files));
 }
 
-int cgroup_task_counter_fork(struct task_struct *child)
+static int task_counter_fork(struct cgroup_subsys *ss, struct task_struct *child)
 {
 	struct cgroup_subsys_state *css = child->cgroups->subsys[tasks_subsys_id];
 	struct cgroup *cgrp = css->cgroup;
@@ -195,5 +195,6 @@ struct cgroup_subsys tasks_subsys = {
 	.can_attach_task	= task_counter_can_attach_task,
 	.cancel_attach_task	= task_counter_cancel_attach_task,
 	.attach_task		= task_counter_attach_task,
+	.fork			= task_counter_fork,
 	.populate		= task_counter_populate,
 };
diff --git a/kernel/fork.c b/kernel/fork.c
index 989c5a0..ee8abdb 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1310,10 +1310,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	p->group_leader = p;
 	INIT_LIST_HEAD(&p->thread_group);
 
-	retval = cgroup_task_counter_fork(p);
-	if (retval)
-		goto bad_fork_free_pid;
-
 	/* Now that the task is set up, run cgroup callbacks if
 	 * necessary. We need to run them before the task is visible
 	 * on the tasklist. */
-- 
1.7.5.4