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cgroup: only need to check oldcgrp==newgrp once

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In cgroup_attach_proc it is now sufficient to only check that
oldcgrp==newcgrp once. Now that we are using threadgroup_lock()
during the migrations, oldcgrp will not change.

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 20:18:37 -08:00 committed by Tejun Heo
parent b07ef77411
commit 892a2b90ba
1 changed files with 6 additions and 16 deletions
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22
kernel/cgroup.c
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@ -2067,7 +2067,7 @@ static int css_set_prefetch(struct cgroup *cgrp, struct css_set *cg,
*/
int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
{
int retval, i, group_size, nr_migrating_tasks;
int retval, i, group_size;
struct cgroup_subsys *ss, *failed_ss = NULL;
/* guaranteed to be initialized later, but the compiler needs this */
struct css_set *oldcg;
@ -2118,7 +2118,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
}
tsk = leader;
i = nr_migrating_tasks = 0;
i = 0;
do {
struct task_and_cgroup ent;
@ -2134,11 +2134,12 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
*/
ent.task = tsk;
ent.cgrp = task_cgroup_from_root(tsk, root);
/* nothing to do if this task is already in the cgroup */
if (ent.cgrp == cgrp)
continue;
retval = flex_array_put(group, i, &ent, GFP_ATOMIC);
BUG_ON(retval != 0);
i++;
if (ent.cgrp != cgrp)
nr_migrating_tasks++;
} while_each_thread(leader, tsk);
/* remember the number of threads in the array for later. */
group_size = i;
@ -2148,7 +2149,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
/* methods shouldn't be called if no task is actually migrating */
retval = 0;
if (!nr_migrating_tasks)
if (!group_size)
goto out_free_group_list;
/*
@ -2171,14 +2172,6 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
INIT_LIST_HEAD(&newcg_list);
for (i = 0; i < group_size; i++) {
tc = flex_array_get(group, i);
/* nothing to do if this task is already in the cgroup */
if (tc->cgrp == cgrp)
continue;
/*
* 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;
/* if we don't already have it in the list get a new one */
@ -2194,9 +2187,6 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
*/
for (i = 0; i < group_size; i++) {
tc = flex_array_get(group, i);
/* leave current thread as it is if it's already there */
if (tc->cgrp == cgrp)
continue;
retval = cgroup_task_migrate(cgrp, tc->cgrp, tc->task, true);
BUG_ON(retval);
}