cgroup: use cgroup_lock_live_group(parent) in cgroup_create() (976c06bc) · Commits · 戴 / test

This patch makes cgroup_create() fail if @parent is marked removed. This is to prepare for further updates to cgroup_rmdir() path. Note that this change isn't strictly necessary. cgroup can only be created via mkdir and the removed marking and dentry removal happen without releasing cgroup_mutex, so cgroup_create() can never race with cgroup_rmdir(). Even after the scheduled updates to cgroup_rmdir(), cgroup_mkdir() and cgroup_rmdir() are synchronized by i_mutex rendering the added liveliness check unnecessary. Do it anyway such that locking is contained inside cgroup proper and we don't get nasty surprises if we ever grow another caller of cgroup_create(). Signed-off-by:

Tejun Heo <tj@kernel.org> Reviewed-by:

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

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

Li Zefan <lizefan@huawei.com>

kernel/cgroup.c

+13 −3

Original line number	Diff line number	Diff line
		@@ -3927,6 +3927,18 @@ static long cgroup_create(struct cgroup parent, struct dentry dentry,
		if (!cgrp)
		return -ENOMEM;

		/*
		* Only live parents can have children. Note that the liveliness
		* check isn't strictly necessary because cgroup_mkdir() and
		* cgroup_rmdir() are fully synchronized by i_mutex; however, do it
		* anyway so that locking is contained inside cgroup proper and we
		* don't get nasty surprises if we ever grow another caller.
		*/
		if (!cgroup_lock_live_group(parent)) {
		err = -ENODEV;
		goto err_free;
		}

		/* Grab a reference on the superblock so the hierarchy doesn't
		* get deleted on unmount if there are child cgroups. This
		* can be done outside cgroup_mutex, since the sb can't
		@@ -3934,8 +3946,6 @@ static long cgroup_create(struct cgroup parent, struct dentry dentry,
		* fs */
		atomic_inc(&sb->s_active);

		mutex_lock(&cgroup_mutex);

		init_cgroup_housekeeping(cgrp);

		cgrp->parent = parent;
		@@ -4006,7 +4016,7 @@ static long cgroup_create(struct cgroup parent, struct dentry dentry,

		/* Release the reference count that we took on the superblock */
		deactivate_super(sb);

		err_free:
		kfree(cgrp);
		return err;
		}

Admin message