cgroup: remove subsystem files when remounting cgroup

cgroup_clear_directroy is called by cgroup_d_remove_dir
and cgroup_remount.

when we call cgroup_remount to remount the cgroup,the subsystem
may be unlinked from cgroupfs_root->subsys_list in rebind_subsystem,this
subsystem's files will not be removed in cgroup_clear_directroy.
And the system will panic when we try to access these files.

this patch removes subsystems's files before rebind_subsystems,
if rebind_subsystems failed, repopulate these removed files.

With help from Tejun.

Signed-off-by: Gao feng <gaofeng@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index e1293a9189b6f6835de7f622073fa51e09c007f6..5cc37241a6fb78851c65f51e2c87bf9b93afd0b6 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1349,14 +1349,21 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
                goto out_unlock;
        }
 
+       /*
+        * Clear out the files of subsystems that should be removed, do
+        * this before rebind_subsystems, since rebind_subsystems may
+        * change this hierarchy's subsys_list.
+        */
+       cgroup_clear_directory(cgrp->dentry, false, removed_mask);
+
        ret = rebind_subsystems(root, opts.subsys_mask);
        if (ret) {
+               /* rebind_subsystems failed, re-populate the removed files */
+               cgroup_populate_dir(cgrp, false, removed_mask);
                drop_parsed_module_refcounts(opts.subsys_mask);
                goto out_unlock;
        }
 
-       /* clear out any existing files and repopulate subsystem files */
-       cgroup_clear_directory(cgrp->dentry, false, removed_mask);
        /* re-populate subsystem files */
        cgroup_populate_dir(cgrp, false, added_mask);