linux-kernel - [PATCH RESEND] cgroup: remove subsystem files when remounting cgroup

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Date:	Mon, 3 Dec 2012 09:28:18 +0800
From:	Gao feng <gaofeng@...fujitsu.com>
To:	tj@...nel.org
Cc:	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, lizefan@...wei.com,
	Gao feng <gaofeng@...fujitsu.com>
Subject: [PATCH RESEND] 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@...fujitsu.com>
---
 kernel/cgroup.c |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index e1293a9..afabd2a 100644
--- 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 job 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);
 
-- 
1.7.7.6

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