From 1f779fb28aa07350d72976d304591d216ca86f0e Mon Sep 17 00:00:00 2001 From: Li Zefan Date: Wed, 4 Jun 2014 16:48:15 +0800 Subject: [PATCH] cgroup: don't destroy the default root The default root is allocated and initialized at boot phase, so we shouldn't destroy the default root when it's umounted, otherwise it will lead to disaster. Just try mount and then umount the default root, and the kernel will crash immediately. v2: - No need to check for CSS_NO_REF in cgroup_get/put(). (Tejun) - Better call cgroup_put() for the default root in kill_sb(). (Tejun) - Add a comment. Signed-off-by: Li Zefan Signed-off-by: Tejun Heo --- kernel/cgroup.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index a5f75ac4e793..3f46165829a4 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -1780,8 +1780,11 @@ static void cgroup_kill_sb(struct super_block *sb) * If @root doesn't have any mounts or children, start killing it. * This prevents new mounts by disabling percpu_ref_tryget_live(). * cgroup_mount() may wait for @root's release. + * + * And don't kill the default root. */ - if (css_has_online_children(&root->cgrp.self)) + if (css_has_online_children(&root->cgrp.self) || + root == &cgrp_dfl_root) cgroup_put(&root->cgrp); else percpu_ref_kill(&root->cgrp.self.refcnt); -- 2.11.0