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cgroup: factor out cgroup_drain_offline() from cgroup_subtree_control_write()

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Factor out async css offline draining into cgroup_drain_offline().

* Nest subsystem walk inside child walk.  The child walk will later be
  converted to subtree walk which is a bit more expensive.

* Relocate the draining above subsystem mask preparation, which
  doesn't create any behavior differences but helps further
  refactoring.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Zefan Li <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2016-03-03 09:57:59 -05:00
parent 5531dc915b
commit 1b9b96a12b
1 changed files with 52 additions and 25 deletions
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77
kernel/cgroup.c
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@ -2965,6 +2965,53 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
return ret;
}
/**
* cgroup_drain_offline - wait for previously offlined csses to go away
* @cgrp: parent of the target cgroups
*
* Because css offlining is asynchronous, userland may try to re-enable a
* controller while the previous css is still around. This function drains
* the previous css instances of @cgrp's children.
*
* Must be called with cgroup_mutex held. Returns %false if there were no
* dying css instances. Returns %true if there were one or more and this
* function waited. On %true return, cgroup_mutex has been dropped and
* re-acquired inbetween which anything could have happened. The caller
* typically would have to start over.
*/
static bool cgroup_drain_offline(struct cgroup *cgrp)
{
struct cgroup *dsct;
struct cgroup_subsys *ss;
int ssid;
lockdep_assert_held(&cgroup_mutex);
cgroup_for_each_live_child(dsct, cgrp) {
for_each_subsys(ss, ssid) {
struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
DEFINE_WAIT(wait);
if (!css)
continue;
cgroup_get(dsct);
prepare_to_wait(&dsct->offline_waitq, &wait,
TASK_UNINTERRUPTIBLE);
mutex_unlock(&cgroup_mutex);
schedule();
finish_wait(&dsct->offline_waitq, &wait);
mutex_lock(&cgroup_mutex);
cgroup_put(dsct);
return true;
}
}
return false;
}
/* change the enabled child controllers for a cgroup in the default hierarchy */
static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
char *buf, size_t nbytes,
@ -3050,6 +3097,11 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
goto out_unlock;
}
if (cgroup_drain_offline(cgrp)) {
cgroup_kn_unlock(of->kn);
return restart_syscall();
}
/*
* Update subsys masks and calculate what needs to be done. More
* subsystems than specified may need to be enabled or disabled
@ -3065,31 +3117,6 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
enable |= css_enable;
disable |= css_disable;
/*
* Because css offlining is asynchronous, userland might try to
* re-enable the same controller while the previous instance is
* still around. In such cases, wait till it's gone using
* offline_waitq.
*/
do_each_subsys_mask(ss, ssid, css_enable) {
cgroup_for_each_live_child(child, cgrp) {
DEFINE_WAIT(wait);
if (!cgroup_css(child, ss))
continue;
cgroup_get(child);
prepare_to_wait(&child->offline_waitq, &wait,
TASK_UNINTERRUPTIBLE);
cgroup_kn_unlock(of->kn);
schedule();
finish_wait(&child->offline_waitq, &wait);
cgroup_put(child);
return restart_syscall();
}
} while_each_subsys_mask();
cgrp->subtree_control = new_sc;
cgrp->subtree_ss_mask = new_ss;