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cgroup: move css_set_rwsem locking outside of cgroup_task_migrate()

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Instead of repeatedly locking and unlocking css_set_rwsem inside
cgroup_task_migrate(), update cgroup_attach_task() to grab it outside
of the loop and update cgroup_task_migrate() to use
put_css_set_locked().

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2014-02-13 06:58:41 -05:00
parent 89c5509b0d
commit cb0f1fe9ba
1 changed files with 11 additions and 5 deletions
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16
kernel/cgroup.c
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@ -1715,10 +1715,13 @@ int cgroup_taskset_size(struct cgroup_taskset *tset)
EXPORT_SYMBOL_GPL(cgroup_taskset_size);
/*
/**
* cgroup_task_migrate - move a task from one cgroup to another.
* @old_cgrp; the cgroup @tsk is being migrated from
* @tsk: the task being migrated
* @new_cset: the new css_set @tsk is being attached to
*
* Must be called with cgroup_mutex and threadgroup locked.
* Must be called with cgroup_mutex, threadgroup and css_set_rwsem locked.
*/
static void cgroup_task_migrate(struct cgroup *old_cgrp,
struct task_struct *tsk,
@ -1726,6 +1729,9 @@ static void cgroup_task_migrate(struct cgroup *old_cgrp,
{
struct css_set *old_cset;
lockdep_assert_held(&cgroup_mutex);
lockdep_assert_held(&css_set_rwsem);
/*
* We are synchronized through threadgroup_lock() against PF_EXITING
* setting such that we can't race against cgroup_exit() changing the
@ -1738,9 +1744,7 @@ static void cgroup_task_migrate(struct cgroup *old_cgrp,
rcu_assign_pointer(tsk->cgroups, new_cset);
task_unlock(tsk);
down_write(&css_set_rwsem);
list_move(&tsk->cg_list, &new_cset->tasks);
up_write(&css_set_rwsem);
/*
* We just gained a reference on old_cset by taking it from the
@ -1748,7 +1752,7 @@ static void cgroup_task_migrate(struct cgroup *old_cgrp,
* we're safe to drop it here; it will be freed under RCU.
*/
set_bit(CGRP_RELEASABLE, &old_cgrp->flags);
put_css_set(old_cset, false);
put_css_set_locked(old_cset, false);
}
/**
@ -1871,10 +1875,12 @@ static int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk,
* proceed to move all tasks to the new cgroup. There are no
* failure cases after here, so this is the commit point.
*/
down_write(&css_set_rwsem);
for (i = 0; i < group_size; i++) {
tc = flex_array_get(group, i);
cgroup_task_migrate(tc->cgrp, tc->task, tc->cset);
}
up_write(&css_set_rwsem);
/* nothing is sensitive to fork() after this point. */
/*