[PATCH] cgroups: don't change release_agent when remount failed

[Li Zefan]

Remount can fail in either case:
  - wrong mount options is specified, or option 'noprefix' is changed.
  - a to-be-added subsys is already mounted/active.

When using remount to change 'release_agent', for the above former failure
case, remount will return errno with release_agent unchanged, but for the
latter case, remount will return EBUSY with relase_agent changed, which is
unexpected I think:

 # mount -t cgroup -o cpu xxx /cgrp1
 # mount -t cgroup -o cpuset,release_agent=agent1 yyy /cgrp2
 # cat /cgrp2/release_agent
 agent1
 # mount -t cgroup -o remount,cpuset,noprefix,release_agent=agent2 yyy /cgrp2
 mount: /cgrp2 not mounted already, or bad option
 # cat /cgrp2/release_agent
 agent1     <-- ok
 # mount -t cgroup -o remount,cpu,cpuset,release_agent=agent2 yyy /cgrp2
 mount: /cgrp2 is busy
 # cat /cgrp2/release_agent
 agent2     <-- unexpected!

Signed-off-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
---
 kernel/cgroup.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index ad10c5d..ebb4a4e 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -915,10 +915,11 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
 	}
 
 	ret = rebind_subsystems(root, opts.subsys_bits);
+	if (ret)
+		goto out_unlock;
 
 	/* (re)populate subsystem files */
-	if (!ret)
-		cgroup_populate_dir(cgrp);
+	cgroup_populate_dir(cgrp);
 
 	if (opts.release_agent)
 		strcpy(root->release_agent_path, opts.release_agent);
-- 
1.5.4.rc3
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