[REVIEW][PATCH 3/4] vfs: Add a function to lazily unmount all mounts from any dentry. v3

[ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman)]

v2: Always drop the lock when exiting early.
v3: Make detach_mounts robust about freeing several
    mounts on the same mountpoint at one time, and remove
    the unneeded mnt_list list test.

Signed-off-by: Eric W. Biederman <ebiederman-1v8oiQdgUNlBDgjK7y7TUQ@public.gmane.org>
---
 fs/mount.h     |    1 +
 fs/namespace.c |   24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+), 0 deletions(-)

diff --git a/fs/mount.h b/fs/mount.h
index e4342b8dfab1..7a6a2bb3f290 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -79,6 +79,7 @@ static inline int is_mounted(struct vfsmount *mnt)
 }
 
 extern struct mount *__lookup_mnt(struct vfsmount *, struct dentry *, int);
+extern void detach_mounts(struct dentry *dentry);
 
 static inline void get_mnt_ns(struct mnt_namespace *ns)
 {
diff --git a/fs/namespace.c b/fs/namespace.c
index e4fe22c23e00..78f7c5c9e673 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1295,6 +1295,30 @@ static int do_umount(struct mount *mnt, int flags)
 	return retval;
 }
 
+void detach_mounts(struct dentry *dentry)
+{
+	struct mountpoint *mp;
+	struct mount *mnt;
+
+	namespace_lock();
+	if (!d_mountpoint(dentry))
+		goto out_unlock;
+
+	mp = new_mountpoint(dentry);
+	if (IS_ERR(mp))
+		goto out_unlock;
+
+	br_write_lock(&vfsmount_lock);
+	while (!list_empty(&mp->m_list)) {
+		mnt = list_first_entry(&mp->m_list, struct mount, mnt_mp_list);
+		umount_tree(mnt, 1);
+	}
+	br_write_unlock(&vfsmount_lock);
+	put_mountpoint(mp);
+out_unlock:
+	namespace_unlock();
+}
+
 /* 
  * Is the caller allowed to modify his namespace?
  */
-- 
1.7.5.4