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, 10 insertions, 8 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 9fe58c46a42..512bd59e862 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1371,10 +1371,10 @@ static int fmeter_getrate(struct fmeter *fmp)
 }
 
 /* Called by cgroups to determine if a cpuset is usable; cgroup_mutex held */
-static int cpuset_can_attach(struct cgroup_subsys *ss, struct cgroup *cont,
-                             struct task_struct *tsk)
+static int cpuset_can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
+                             struct cgroup_taskset *tset)
 {
-        struct cpuset *cs = cgroup_cs(cont);
+        struct cpuset *cs = cgroup_cs(cgrp);
 
         if (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))
                 return -ENOSPC;
@@ -1387,7 +1387,7 @@ static int cpuset_can_attach(struct cgroup_subsys *ss, struct cgroup *cont,
          * set_cpus_allowed_ptr() on all attached tasks before cpus_allowed may
          * be changed.
          */
-        if (tsk->flags & PF_THREAD_BOUND)
+        if (cgroup_taskset_first(tset)->flags & PF_THREAD_BOUND)
                 return -EINVAL;
 
         return 0;
@@ -1437,12 +1437,14 @@ static void cpuset_attach_task(struct cgroup *cont, struct task_struct *tsk)
         cpuset_update_task_spread_flag(cs, tsk);
 }
 
-static void cpuset_attach(struct cgroup_subsys *ss, struct cgroup *cont,
-                          struct cgroup *oldcont, struct task_struct *tsk)
+static void cpuset_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
+                          struct cgroup_taskset *tset)
 {
         struct mm_struct *mm;
-        struct cpuset *cs = cgroup_cs(cont);
-        struct cpuset *oldcs = cgroup_cs(oldcont);
+        struct task_struct *tsk = cgroup_taskset_first(tset);
+        struct cgroup *oldcgrp = cgroup_taskset_cur_cgroup(tset);
+        struct cpuset *cs = cgroup_cs(cgrp);
+        struct cpuset *oldcs = cgroup_cs(oldcgrp);
 
         /*
          * Change mm, possibly for multiple threads in a threadgroup. This is