cgroup: introduce cgroup_taskset and use it in subsys->can_attach(), cancel_attach() and attach()

Currently, there's no way to pass multiple tasks to cgroup_subsys
methods necessitating the need for separate per-process and per-task
methods.  This patch introduces cgroup_taskset which can be used to
pass multiple tasks and their associated cgroups to cgroup_subsys
methods.

Three methods - can_attach(), cancel_attach() and attach() - are
converted to use cgroup_taskset.  This unifies passed parameters so
that all methods have access to all information.  Conversions in this
patchset are identical and don't introduce any behavior change.

-v2: documentation updated as per Paul Menage's suggestion.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Paul Menage <paul@paulmenage.org>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: James Morris <jmorris@namei.org>

1 files changed, 8 insertions, 8 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6aff93c98aca..81640e74a709 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5298,8 +5298,9 @@ static void mem_cgroup_clear_mc(void)
 
 static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
                                 struct cgroup *cgroup,
-                                struct task_struct *p)
+                                struct cgroup_taskset *tset)
 {
+        struct task_struct *p = cgroup_taskset_first(tset);
         int ret = 0;
         struct mem_cgroup *memcg = mem_cgroup_from_cont(cgroup);
 
@@ -5337,7 +5338,7 @@ static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
 
 static void mem_cgroup_cancel_attach(struct cgroup_subsys *ss,
                                 struct cgroup *cgroup,
-                                struct task_struct *p)
+                                struct cgroup_taskset *tset)
 {
         mem_cgroup_clear_mc();
 }
@@ -5454,9 +5455,9 @@ retry:
 
 static void mem_cgroup_move_task(struct cgroup_subsys *ss,
                                 struct cgroup *cont,
-                                struct cgroup *old_cont,
-                                struct task_struct *p)
+                                struct cgroup_taskset *tset)
 {
+        struct task_struct *p = cgroup_taskset_first(tset);
         struct mm_struct *mm = get_task_mm(p);
 
         if (mm) {
@@ -5471,19 +5472,18 @@ static void mem_cgroup_move_task(struct cgroup_subsys *ss,
 #else   /* !CONFIG_MMU */
 static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
                                 struct cgroup *cgroup,
-                                struct task_struct *p)
+                                struct cgroup_taskset *tset)
 {
         return 0;
 }
 static void mem_cgroup_cancel_attach(struct cgroup_subsys *ss,
                                 struct cgroup *cgroup,
-                                struct task_struct *p)
+                                struct cgroup_taskset *tset)
 {
 }
 static void mem_cgroup_move_task(struct cgroup_subsys *ss,
                                 struct cgroup *cont,
-                                struct cgroup *old_cont,
-                                struct task_struct *p)
+                                struct cgroup_taskset *tset)
 {
 }
 #endif