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>

4 files changed, 63 insertions, 65 deletions

diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index e95c6fb65cc0..0e748059ba87 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -162,10 +162,14 @@ static int freezer_can_attach(struct cgroup_subsys *ss,
                               struct cgroup_taskset *tset)
 {
         struct freezer *freezer;
+        struct task_struct *task;
 
         /*
          * Anything frozen can't move or be moved to/from.
          */
+        cgroup_taskset_for_each(task, new_cgroup, tset)
+                if (cgroup_freezing(task))
+                        return -EBUSY;
 
         freezer = cgroup_freezer(new_cgroup);
         if (freezer->state != CGROUP_THAWED)
@@ -174,11 +178,6 @@ static int freezer_can_attach(struct cgroup_subsys *ss,
         return 0;
 }
 
-static int freezer_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
-{
-        return cgroup_freezing(tsk) ? -EBUSY : 0;
-}
-
 static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
 {
         struct freezer *freezer;
@@ -374,10 +373,5 @@ 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,
 };
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 512bd59e8627..9a8a61301524 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1375,33 +1375,34 @@ static int cpuset_can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
                              struct cgroup_taskset *tset)
 {
         struct cpuset *cs = cgroup_cs(cgrp);
+        struct task_struct *task;
+        int ret;
 
         if (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))
                 return -ENOSPC;
 
-        /*
-         * Kthreads bound to specific cpus cannot be moved to a new cpuset; we
-         * cannot change their cpu affinity and isolating such threads by their
-         * set of allowed nodes is unnecessary.  Thus, cpusets are not
-         * applicable for such threads.  This prevents checking for success of
-         * set_cpus_allowed_ptr() on all attached tasks before cpus_allowed may
-         * be changed.
-         */
-        if (cgroup_taskset_first(tset)->flags & PF_THREAD_BOUND)
-                return -EINVAL;
-
+        cgroup_taskset_for_each(task, cgrp, tset) {
+                /*
+                 * Kthreads bound to specific cpus cannot be moved to a new
+                 * cpuset; we cannot change their cpu affinity and
+                 * isolating such threads by their set of allowed nodes is
+                 * unnecessary.  Thus, cpusets are not applicable for such
+                 * threads.  This prevents checking for success of
+                 * set_cpus_allowed_ptr() on all attached tasks before
+                 * cpus_allowed may be changed.
+                 */
+                if (task->flags & PF_THREAD_BOUND)
+                        return -EINVAL;
+                if ((ret = security_task_setscheduler(task)))
+                        return ret;
+        }
         return 0;
 }
 
-static int cpuset_can_attach_task(struct cgroup *cgrp, struct task_struct *task)
-{
-        return security_task_setscheduler(task);
-}
-
 /*
  * Protected by cgroup_lock. The nodemasks must be stored globally because
  * dynamically allocating them is not allowed in pre_attach, and they must
- * persist among pre_attach, attach_task, and attach.
+ * persist among pre_attach, and attach.
  */
 static cpumask_var_t cpus_attach;
 static nodemask_t cpuset_attach_nodemask_from;
@@ -1420,39 +1421,34 @@ static void cpuset_pre_attach(struct cgroup *cont)
         guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
 }
 
-/* Per-thread attachment work. */
-static void cpuset_attach_task(struct cgroup *cont, struct task_struct *tsk)
-{
-        int err;
-        struct cpuset *cs = cgroup_cs(cont);
-
-        /*
-         * can_attach beforehand should guarantee that this doesn't fail.
-         * TODO: have a better way to handle failure here
-         */
-        err = set_cpus_allowed_ptr(tsk, cpus_attach);
-        WARN_ON_ONCE(err);
-
-        cpuset_change_task_nodemask(tsk, &cpuset_attach_nodemask_to);
-        cpuset_update_task_spread_flag(cs, tsk);
-}
-
 static void cpuset_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
                           struct cgroup_taskset *tset)
 {
         struct mm_struct *mm;
-        struct task_struct *tsk = cgroup_taskset_first(tset);
+        struct task_struct *task;
+        struct task_struct *leader = cgroup_taskset_first(tset);
         struct cgroup *oldcgrp = cgroup_taskset_cur_cgroup(tset);
         struct cpuset *cs = cgroup_cs(cgrp);
         struct cpuset *oldcs = cgroup_cs(oldcgrp);
 
+        cgroup_taskset_for_each(task, cgrp, tset) {
+                /*
+                 * can_attach beforehand should guarantee that this doesn't
+                 * fail.  TODO: have a better way to handle failure here
+                 */
+                WARN_ON_ONCE(set_cpus_allowed_ptr(task, cpus_attach));
+
+                cpuset_change_task_nodemask(task, &cpuset_attach_nodemask_to);
+                cpuset_update_task_spread_flag(cs, task);
+        }
+
         /*
          * Change mm, possibly for multiple threads in a threadgroup. This is
          * expensive and may sleep.
          */
         cpuset_attach_nodemask_from = oldcs->mems_allowed;
         cpuset_attach_nodemask_to = cs->mems_allowed;
-        mm = get_task_mm(tsk);
+        mm = get_task_mm(leader);
         if (mm) {
                 mpol_rebind_mm(mm, &cpuset_attach_nodemask_to);
                 if (is_memory_migrate(cs))
@@ -1908,9 +1904,7 @@ struct cgroup_subsys cpuset_subsys = {
         .create = cpuset_create,
         .destroy = cpuset_destroy,
         .can_attach = cpuset_can_attach,
-        .can_attach_task = cpuset_can_attach_task,
         .pre_attach = cpuset_pre_attach,
-        .attach_task = cpuset_attach_task,
         .attach = cpuset_attach,
         .populate = cpuset_populate,
         .post_clone = cpuset_post_clone,
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 0e8457da6f95..3b8e0edbe693 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7044,10 +7044,13 @@ static int __perf_cgroup_move(void *info)
         return 0;
 }
 
-static void
-perf_cgroup_attach_task(struct cgroup *cgrp, struct task_struct *task)
+static void perf_cgroup_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
+                               struct cgroup_taskset *tset)
 {
-        task_function_call(task, __perf_cgroup_move, task);
+        struct task_struct *task;
+
+        cgroup_taskset_for_each(task, cgrp, tset)
+                task_function_call(task, __perf_cgroup_move, task);
 }
 
 static void perf_cgroup_exit(struct cgroup_subsys *ss, struct cgroup *cgrp,
@@ -7061,7 +7064,7 @@ static void perf_cgroup_exit(struct cgroup_subsys *ss, struct cgroup *cgrp,
         if (!(task->flags & PF_EXITING))
                 return;
 
-        perf_cgroup_attach_task(cgrp, task);
+        task_function_call(task, __perf_cgroup_move, task);
 }
 
 struct cgroup_subsys perf_subsys = {
@@ -7070,6 +7073,6 @@ struct cgroup_subsys perf_subsys = {
         .create         = perf_cgroup_create,
         .destroy        = perf_cgroup_destroy,
         .exit           = perf_cgroup_exit,
-        .attach_task    = perf_cgroup_attach_task,
+        .attach         = perf_cgroup_attach,
 };
 #endif /* CONFIG_CGROUP_PERF */
diff --git a/kernel/sched.c b/kernel/sched.c
index 0e9344a71be3..161184da7b81 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -9127,24 +9127,31 @@ cpu_cgroup_destroy(struct cgroup_subsys *ss, struct cgroup *cgrp)
         sched_destroy_group(tg);
 }
 
-static int
-cpu_cgroup_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
+static int cpu_cgroup_can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
+                                 struct cgroup_taskset *tset)
 {
+        struct task_struct *task;
+
+        cgroup_taskset_for_each(task, cgrp, tset) {
 #ifdef CONFIG_RT_GROUP_SCHED
-        if (!sched_rt_can_attach(cgroup_tg(cgrp), tsk))
-                return -EINVAL;
+                if (!sched_rt_can_attach(cgroup_tg(cgrp), task))
+                        return -EINVAL;
 #else
-        /* We don't support RT-tasks being in separate groups */
-        if (tsk->sched_class != &fair_sched_class)
-                return -EINVAL;
+                /* We don't support RT-tasks being in separate groups */
+                if (task->sched_class != &fair_sched_class)
+                        return -EINVAL;
 #endif
+        }
         return 0;
 }
 
-static void
-cpu_cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
+static void cpu_cgroup_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
+                              struct cgroup_taskset *tset)
 {
-        sched_move_task(tsk);
+        struct task_struct *task;
+
+        cgroup_taskset_for_each(task, cgrp, tset)
+                sched_move_task(task);
 }
 
 static void
@@ -9480,8 +9487,8 @@ struct cgroup_subsys cpu_cgroup_subsys = {
         .name           = "cpu",
         .create         = cpu_cgroup_create,
         .destroy        = cpu_cgroup_destroy,
-        .can_attach_task = cpu_cgroup_can_attach_task,
-        .attach_task    = cpu_cgroup_attach_task,
+        .can_attach     = cpu_cgroup_can_attach,
+        .attach         = cpu_cgroup_attach,
         .exit           = cpu_cgroup_exit,
         .populate       = cpu_cgroup_populate,
         .subsys_id      = cpu_cgroup_subsys_id,