cgroup, cpuset: don't use ss->pre_attach()

->pre_attach() is supposed to be called before migration, which is
observed during process migration but task migration does it the other
way around.  The only ->pre_attach() user is cpuset which can do the
same operaitons in ->can_attach().  Collapse cpuset_pre_attach() into
cpuset_can_attach().

-v2: Patch contamination from later patch removed.  Spotted by Paul
     Menage.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Paul Menage <paul@paulmenage.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>

1 files changed, 12 insertions, 17 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 9a8a61301524..42e568306382 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1370,6 +1370,15 @@ static int fmeter_getrate(struct fmeter *fmp)
         return val;
 }
 
+/*
+ * Protected by cgroup_lock. The nodemasks must be stored globally because
+ * dynamically allocating them is not allowed in can_attach, and they must
+ * persist until attach.
+ */
+static cpumask_var_t cpus_attach;
+static nodemask_t cpuset_attach_nodemask_from;
+static nodemask_t cpuset_attach_nodemask_to;
+
 /* Called by cgroups to determine if a cpuset is usable; cgroup_mutex held */
 static int cpuset_can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
                              struct cgroup_taskset *tset)
@@ -1396,29 +1405,16 @@ static int cpuset_can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
                 if ((ret = security_task_setscheduler(task)))
                         return ret;
         }
-        return 0;
-}
-
-/*
- * 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, and attach.
- */
-static cpumask_var_t cpus_attach;
-static nodemask_t cpuset_attach_nodemask_from;
-static nodemask_t cpuset_attach_nodemask_to;
-
-/* Set-up work for before attaching each task. */
-static void cpuset_pre_attach(struct cgroup *cont)
-{
-        struct cpuset *cs = cgroup_cs(cont);
 
+        /* prepare for attach */
         if (cs == &top_cpuset)
                 cpumask_copy(cpus_attach, cpu_possible_mask);
         else
                 guarantee_online_cpus(cs, cpus_attach);
 
         guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
+
+        return 0;
 }
 
 static void cpuset_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
@@ -1904,7 +1900,6 @@ struct cgroup_subsys cpuset_subsys = {
         .create = cpuset_create,
         .destroy = cpuset_destroy,
         .can_attach = cpuset_can_attach,
-        .pre_attach = cpuset_pre_attach,
         .attach = cpuset_attach,
         .populate = cpuset_populate,
         .post_clone = cpuset_post_clone,