cgroups: add per-thread subsystem callbacks

Add cgroup subsystem callbacks for per-thread attachment in atomic contexts

Add can_attach_task(), pre_attach(), and attach_task() as new callbacks
for cgroups's subsystem interface.  Unlike can_attach and attach, these
are for per-thread operations, to be called potentially many times when
attaching an entire threadgroup.

Also, the old "bool threadgroup" interface is removed, as replaced by
this.  All subsystems are modified for the new interface - of note is
cpuset, which requires from/to nodemasks for attach to be globally scoped
(though per-cpuset would work too) to persist from its pre_attach to
attach_task and attach.

This is a pre-patch for cgroup-procs-writable.patch.

Signed-off-by: Ben Blum <bblum@andrew.cmu.edu>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Reviewed-by: Paul Menage <menage@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 35 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 2d12893b8b0f..5e43e9dc65d1 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -8764,42 +8764,10 @@ cpu_cgroup_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
         return 0;
 }
 
-static int
-cpu_cgroup_can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
-                      struct task_struct *tsk, bool threadgroup)
-{
-        int retval = cpu_cgroup_can_attach_task(cgrp, tsk);
-        if (retval)
-                return retval;
-        if (threadgroup) {
-                struct task_struct *c;
-                rcu_read_lock();
-                list_for_each_entry_rcu(c, &tsk->thread_group, thread_group) {
-                        retval = cpu_cgroup_can_attach_task(cgrp, c);
-                        if (retval) {
-                                rcu_read_unlock();
-                                return retval;
-                        }
-                }
-                rcu_read_unlock();
-        }
-        return 0;
-}
-
 static void
-cpu_cgroup_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
-                  struct cgroup *old_cont, struct task_struct *tsk,
-                  bool threadgroup)
+cpu_cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
 {
         sched_move_task(tsk);
-        if (threadgroup) {
-                struct task_struct *c;
-                rcu_read_lock();
-                list_for_each_entry_rcu(c, &tsk->thread_group, thread_group) {
-                        sched_move_task(c);
-                }
-                rcu_read_unlock();
-        }
 }
 
 static void
@@ -8887,8 +8855,8 @@ struct cgroup_subsys cpu_cgroup_subsys = {
         .name           = "cpu",
         .create         = cpu_cgroup_create,
         .destroy        = cpu_cgroup_destroy,
-        .can_attach     = cpu_cgroup_can_attach,
-        .attach         = cpu_cgroup_attach,
+        .can_attach_task = cpu_cgroup_can_attach_task,
+        .attach_task    = cpu_cgroup_attach_task,
         .exit           = cpu_cgroup_exit,
         .populate       = cpu_cgroup_populate,
         .subsys_id      = cpu_cgroup_subsys_id,