cgroup: make sure parent won't be destroyed before its children (415cf07a) · Commits · 戴 / test

Suppose we rmdir a cgroup and there're still css refs, this cgroup won't be freed. Then we rmdir the parent cgroup, and the parent is freed immediately due to css ref draining to 0. Now it would be a disaster if the still-alive child cgroup tries to access its parent. Make sure this won't happen. Signed-off-by:

Li Zefan <lizefan@huawei.com> Reviewed-by:

Michal Hocko <mhocko@suse.cz> Acked-by:

KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Signed-off-by:

Tejun Heo <tj@kernel.org>

kernel/cgroup.c

+10 −0

Original line number	Original line	Diff line number	Diff line
	@@ -875,6 +875,13 @@ static void cgroup_free_fn(struct work_struct *work)
	cgrp->root->number_of_cgroups--;		cgrp->root->number_of_cgroups--;
	mutex_unlock(&cgroup_mutex);		mutex_unlock(&cgroup_mutex);

			/*
			* We get a ref to the parent's dentry, and put the ref when
			* this cgroup is being freed, so it's guaranteed that the
			* parent won't be destroyed before its children.
			*/
			dput(cgrp->parent->dentry);

	/*		/*
	* Drop the active superblock reference that we took when we		* Drop the active superblock reference that we took when we
	* created the cgroup		* created the cgroup
	@@ -4164,6 +4171,9 @@ static long cgroup_create(struct cgroup parent, struct dentry dentry,
	for_each_subsys(root, ss)		for_each_subsys(root, ss)
	dget(dentry);		dget(dentry);

			/* hold a ref to the parent's dentry */
			dget(parent->dentry);

	/* creation succeeded, notify subsystems */		/* creation succeeded, notify subsystems */
	for_each_subsys(root, ss) {		for_each_subsys(root, ss) {
	err = online_css(ss, cgrp);		err = online_css(ss, cgrp);

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