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cgroup: remove redundant get/put of old css_set from migrate

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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>
This commit is contained in:
Mandeep Singh Baines 2011-12-21 20:18:35 -08:00 committed by Tejun Heo
parent c84cdf75cc
commit 026085ef5a
1 changed files with 8 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
kernel/cgroup.c
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@ -1850,14 +1850,12 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
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 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
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 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
* 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;
}
}
/*