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cgroup: make sure a parent css isn't freed before its children

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There are three subsystem callbacks in css shutdown path -
css_offline(), css_released() and css_free().  Except for
css_released(), cgroup core didn't guarantee the order of invocation.
css_offline() or css_free() could be called on a parent css before its
children.  This behavior is unexpected and led to bugs in cpu and
memory controller.

The previous patch updated ordering for css_offline() which fixes the
cpu controller issue.  While there currently isn't a known bug caused
by misordering of css_free() invocations, let's fix it too for
consistency.

css_free() ordering can be trivially fixed by moving putting of the
parent css below css_free() invocation.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
This commit is contained in:
Tejun Heo 2016-01-21 15:32:15 -05:00
parent aa226ff4a1
commit 8bb5ef79bc
1 changed files with 4 additions and 3 deletions
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7
kernel/cgroup.c
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@ -4657,14 +4657,15 @@ static void css_free_work_fn(struct work_struct *work)
if (ss) {
/* css free path */
struct cgroup_subsys_state *parent = css->parent;
int id = css->id;
if (css->parent)
css_put(css->parent);
ss->css_free(css);
cgroup_idr_remove(&ss->css_idr, id);
cgroup_put(cgrp);
if (parent)
css_put(parent);
} else {
/* cgroup free path */
atomic_dec(&cgrp->root->nr_cgrps);