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cgroup: Remove unnecessary task_lock before fetching css_set on migration 

When we fetch the css_set of the tasks on cgroup migration, we don't need
anymore to synchronize against cgroup_exit() that could swap the old one
with init_css_set. Now that we are using threadgroup_lock() during
the migrations, we don't need to worry about it anymore.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: Mandeep Singh Baines <msb@chromium.org>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Containers <containers@lists.linux-foundation.org>
Cc: Cgroups <cgroups@vger.kernel.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Menage <paul@paulmenage.org>
This commit is contained in:
Frederic Weisbecker 2011-12-21 20:03:18 +01:00 committed by Tejun Heo
parent 7e381b0eb1
commit c84cdf75cc
1 changed files with 10 additions and 10 deletions
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20
kernel/cgroup.c
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@ -1850,14 +1850,14 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
struct css_set *newcg;
/*
* get old css_set. we need to take task_lock and refcount it, because
* an exiting task can change its css_set to init_css_set and drop its
* old one without taking cgroup_mutex.
* 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.
*/
task_lock(tsk);
WARN_ON_ONCE(tsk->flags & PF_EXITING);
oldcg = tsk->cgroups;
get_css_set(oldcg);
task_unlock(tsk);
/* locate or allocate a new css_set for this task. */
if (guarantee) {
@ -1879,9 +1879,7 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
}
put_css_set(oldcg);
/* @tsk can't exit as its threadgroup is locked */
task_lock(tsk);
WARN_ON_ONCE(tsk->flags & PF_EXITING);
rcu_assign_pointer(tsk->cgroups, newcg);
task_unlock(tsk);
@ -2182,11 +2180,13 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
/* nothing to do if this task is already in the cgroup */
if (tc->cgrp == cgrp)
continue;
/* get old css_set pointer */
task_lock(tc->task);
/*
* get old css_set pointer. threadgroup is locked so this is
* safe against concurrent cgroup_exit() changing this to
* init_css_set.
*/
oldcg = tc->task->cgroups;
get_css_set(oldcg);
task_unlock(tc->task);
/* 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. */