Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 4.4 108/163] cgroup: make sure a parent css isnt freed before its children | Date | Mon, 2 May 2016 17:12:16 -0700 |
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4.4-stable review patch. If anyone has any objections, please let me know.
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From: Tejun Heo <tj@kernel.org>
commit 8bb5ef79bc0f4016ecf79e8dce6096a3c63603e4 upstream.
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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- kernel/cgroup.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
--- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4692,14 +4692,15 @@ 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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