Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Tejun Heo , Peter Zijlstra 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 Message-Id: <20160503000512.051650879@linuxfoundation.org> In-Reply-To: <20160503000508.556845508@linuxfoundation.org> References: <20160503000508.556845508@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tejun Heo 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 Cc: Peter Zijlstra Signed-off-by: Greg Kroah-Hartman --- 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);