cpuset: cleanup cpuset[_can]_attach()

cpuset_can_attach() prepare global variables cpus_attach and
cpuset_attach_nodemask_{to|from} which are used by cpuset_attach().
There is no reason to prepare in cpuset_can_attach().  The same
information can be accessed from cpuset_attach().

Move the prepartion logic from cpuset_can_attach() to cpuset_attach()
and make the global variables static ones inside cpuset_attach().

With this change, there's no reason to keep
cpuset_attach_nodemask_{from|to} global.  Move them inside
cpuset_attach().  Unfortunately, we need to keep cpus_attach global as
it can't be allocated from cpuset_attach().

v2: cpus_attach not converted to cpumask_t as per Li Zefan and Rusty
    Russell.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 18 insertions, 17 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 4b054b9faf3d..c5edc6b3eb28 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1395,15 +1395,6 @@ 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 *cgrp, struct cgroup_taskset *tset)
 {
@@ -1430,19 +1421,21 @@ static int cpuset_can_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
                         return ret;
         }
 
-        /* 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;
 }
 
+/*
+ * Protected by cgroup_mutex.  cpus_attach is used only by cpuset_attach()
+ * but we can't allocate it dynamically there.  Define it global and
+ * allocate from cpuset_init().
+ */
+static cpumask_var_t cpus_attach;
+
 static void cpuset_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
 {
+        /* static bufs protected by cgroup_mutex */
+        static nodemask_t cpuset_attach_nodemask_from;
+        static nodemask_t cpuset_attach_nodemask_to;
         struct mm_struct *mm;
         struct task_struct *task;
         struct task_struct *leader = cgroup_taskset_first(tset);
@@ -1450,6 +1443,14 @@ static void cpuset_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
         struct cpuset *cs = cgroup_cs(cgrp);
         struct cpuset *oldcs = cgroup_cs(oldcgrp);
 
+        /* 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);
+
         cgroup_taskset_for_each(task, cgrp, tset) {
                 /*
                  * can_attach beforehand should guarantee that this doesn't