cgroup: remove redundant get/put of old css_set from migrate
We can now assume that the css_set reference held by the task
will not go away for an exiting task. PF_EXITING state can be
trusted throughout migration by checking it after locking
threadgroup.
Changes in V4:
* https://lkml.org/lkml/2011/12/20/368 (Tejun Heo)
* Fix typo in commit message
* Undid the rename of css_set_check_fetched
* https://lkml.org/lkml/2011/12/20/427 (Li Zefan)
* Fix comment in cgroup_task_migrate()
Changes in V3:
* https://lkml.org/lkml/2011/12/20/255 (Frederic Weisbecker)
* Fixed to put error in retval
Changes in V2:
* https://lkml.org/lkml/2011/12/19/289 (Tejun Heo)
* Updated commit message
-tj: removed stale patch description about dropped function rename.
Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: containers@lists.linux-foundation.org
Cc: cgroups@vger.kernel.org
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Menage <paul@paulmenage.org>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 4936d88..8228808 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1850,14 +1850,12 @@
struct css_set *newcg;
/*
- * get old css_set. We are synchronized through threadgroup_lock()
- * against PF_EXITING setting such that we can't race against
- * cgroup_exit() changing the css_set to init_css_set and dropping the
- * old one.
+ * We are synchronized through threadgroup_lock() against PF_EXITING
+ * setting such that we can't race against cgroup_exit() changing the
+ * css_set to init_css_set and dropping the old one.
*/
WARN_ON_ONCE(tsk->flags & PF_EXITING);
oldcg = tsk->cgroups;
- get_css_set(oldcg);
/* locate or allocate a new css_set for this task. */
if (guarantee) {
@@ -1872,12 +1870,9 @@
might_sleep();
/* find_css_set will give us newcg already referenced. */
newcg = find_css_set(oldcg, cgrp);
- if (!newcg) {
- put_css_set(oldcg);
+ if (!newcg)
return -ENOMEM;
- }
}
- put_css_set(oldcg);
task_lock(tsk);
rcu_assign_pointer(tsk->cgroups, newcg);
@@ -2186,18 +2181,11 @@
* init_css_set.
*/
oldcg = tc->task->cgroups;
- get_css_set(oldcg);
- /* see if the new one for us is already in the list? */
- if (css_set_check_fetched(cgrp, tc->task, oldcg, &newcg_list)) {
- /* was already there, nothing to do. */
- put_css_set(oldcg);
- } else {
- /* we don't already have it. get new one. */
- retval = css_set_prefetch(cgrp, oldcg, &newcg_list);
- put_css_set(oldcg);
- if (retval)
+
+ /* if we don't already have it in the list get a new one */
+ if (!css_set_check_fetched(cgrp, tc->task, oldcg, &newcg_list))
+ if (retval = css_set_prefetch(cgrp, oldcg, &newcg_list))
goto out_list_teardown;
- }
}
/*