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cgroup: fix top cgroup refcnt leak

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As mount() and kill_sb() is not a one-to-one match, If we mount the same
cgroupfs in serveral mount points, and then umount all of them, kill_sb()
will be called only once.

Try:
        # mount -t cgroup -o cpuacct xxx /cgroup
        # mount -t cgroup -o cpuacct xxx /cgroup2
        # cat /proc/cgroups | grep cpuacct
        cpuacct 2       1       1
        # umount /cgroup
        # umount /cgroup2
        # cat /proc/cgroups | grep cpuacct
        cpuacct 2       1       1

You'll see cgroupfs will never be freed.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Li Zefan
2014-04-04 17:14:41 +08:00
committed by Tejun Heo
parent 4a4389abdd
commit c6b3d5bcd6
1 changed files with 3 additions and 2 deletions
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kernel/cgroup.c
+3 -2
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@@ -1487,6 +1487,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
struct cgroup_sb_opts opts;
struct dentry *dentry;
int ret;
bool new_sb;
/*
* The first time anyone tries to mount a cgroup, enable the list
@@ -1603,8 +1604,8 @@ out_unlock:
if (ret)
return ERR_PTR(ret);
dentry = kernfs_mount(fs_type, flags, root->kf_root, NULL);
if (IS_ERR(dentry))
dentry = kernfs_mount(fs_type, flags, root->kf_root, &new_sb);
if (IS_ERR(dentry) || !new_sb)
cgroup_put(&root->cgrp);
return dentry;
}