cgroup: don't use subsys->can_attach_task() or ->attach_task()

Now that subsys->can_attach() and attach() take @tset instead of
@task, they can handle per-task operations.  Convert
->can_attach_task() and ->attach_task() users to use ->can_attach()
and attach() instead.  Most converions are straight-forward.
Noteworthy changes are,

* In cgroup_freezer, remove unnecessary NULL assignments to unused
  methods.  It's useless and very prone to get out of sync, which
  already happened.

* In cpuset, PF_THREAD_BOUND test is checked for each task.  This
  doesn't make any practical difference but is conceptually cleaner.

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: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <paul@paulmenage.org>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: James Morris <jmorris@namei.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>

1 files changed, 28 insertions, 17 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 8f630cec906e..b8c143d68ee0 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -30,8 +30,10 @@ EXPORT_SYMBOL_GPL(blkio_root_cgroup);
 
 static struct cgroup_subsys_state *blkiocg_create(struct cgroup_subsys *,
                                                   struct cgroup *);
-static int blkiocg_can_attach_task(struct cgroup *, struct task_struct *);
-static void blkiocg_attach_task(struct cgroup *, struct task_struct *);
+static int blkiocg_can_attach(struct cgroup_subsys *, struct cgroup *,
+                              struct cgroup_taskset *);
+static void blkiocg_attach(struct cgroup_subsys *, struct cgroup *,
+                           struct cgroup_taskset *);
 static void blkiocg_destroy(struct cgroup_subsys *, struct cgroup *);
 static int blkiocg_populate(struct cgroup_subsys *, struct cgroup *);
 
@@ -44,8 +46,8 @@ static int blkiocg_populate(struct cgroup_subsys *, struct cgroup *);
 struct cgroup_subsys blkio_subsys = {
         .name = "blkio",
         .create = blkiocg_create,
-        .can_attach_task = blkiocg_can_attach_task,
-        .attach_task = blkiocg_attach_task,
+        .can_attach = blkiocg_can_attach,
+        .attach = blkiocg_attach,
         .destroy = blkiocg_destroy,
         .populate = blkiocg_populate,
 #ifdef CONFIG_BLK_CGROUP
@@ -1626,30 +1628,39 @@ done:
  * of the main cic data structures.  For now we allow a task to change
  * its cgroup only if it's the only owner of its ioc.
  */
-static int blkiocg_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
+static int blkiocg_can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
+                              struct cgroup_taskset *tset)
 {
+        struct task_struct *task;
         struct io_context *ioc;
         int ret = 0;
 
         /* task_lock() is needed to avoid races with exit_io_context() */
-        task_lock(tsk);
-        ioc = tsk->io_context;
-        if (ioc && atomic_read(&ioc->nr_tasks) > 1)
-                ret = -EINVAL;
-        task_unlock(tsk);
-
+        cgroup_taskset_for_each(task, cgrp, tset) {
+                task_lock(task);
+                ioc = task->io_context;
+                if (ioc && atomic_read(&ioc->nr_tasks) > 1)
+                        ret = -EINVAL;
+                task_unlock(task);
+                if (ret)
+                        break;
+        }
         return ret;
 }
 
-static void blkiocg_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
+static void blkiocg_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
+                           struct cgroup_taskset *tset)
 {
+        struct task_struct *task;
         struct io_context *ioc;
 
-        task_lock(tsk);
-        ioc = tsk->io_context;
-        if (ioc)
-                ioc->cgroup_changed = 1;
-        task_unlock(tsk);
+        cgroup_taskset_for_each(task, cgrp, tset) {
+                task_lock(task);
+                ioc = task->io_context;
+                if (ioc)
+                        ioc->cgroup_changed = 1;
+                task_unlock(task);
+        }
 }
 
 void blkio_policy_register(struct blkio_policy_type *blkiop)