There are three subsystem callbacks in css shutdown path -
css_offline(), css_released() and css_free(). Except for
css_released(), cgroup core didn't use to 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
use-after-free in cpu 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@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
---
kernel/cgroup.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4657,14 +4657,15 @@ static void css_free_work_fn(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);
--
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