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, 10 insertions, 16 deletions

diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index e7bebb7c6c38..e691818d7e45 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -160,7 +160,7 @@ static void freezer_destroy(struct cgroup_subsys *ss,
  */
 static int freezer_can_attach(struct cgroup_subsys *ss,
                               struct cgroup *new_cgroup,
-                              struct task_struct *task, bool threadgroup)
+                              struct task_struct *task)
 {
         struct freezer *freezer;
 
@@ -172,26 +172,17 @@ static int freezer_can_attach(struct cgroup_subsys *ss,
         if (freezer->state != CGROUP_THAWED)
                 return -EBUSY;
 
+        return 0;
+}
+
+static int freezer_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
+{
         rcu_read_lock();
-        if (__cgroup_freezing_or_frozen(task)) {
+        if (__cgroup_freezing_or_frozen(tsk)) {
                 rcu_read_unlock();
                 return -EBUSY;
         }
         rcu_read_unlock();
-
-        if (threadgroup) {
-                struct task_struct *c;
-
-                rcu_read_lock();
-                list_for_each_entry_rcu(c, &task->thread_group, thread_group) {
-                        if (__cgroup_freezing_or_frozen(c)) {
-                                rcu_read_unlock();
-                                return -EBUSY;
-                        }
-                }
-                rcu_read_unlock();
-        }
-
         return 0;
 }
 
@@ -390,6 +381,9 @@ struct cgroup_subsys freezer_subsys = {
         .populate       = freezer_populate,
         .subsys_id      = freezer_subsys_id,
         .can_attach     = freezer_can_attach,
+        .can_attach_task = freezer_can_attach_task,
+        .pre_attach     = NULL,
+        .attach_task    = NULL,
         .attach         = NULL,
         .fork           = freezer_fork,
         .exit           = NULL,