[PATCH 05/11] vfs: Add a function to lazily unmount all mounts from any dentry.

[ebiederm@xmission.com (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.
v4: Document the purpose of detach_mounts and why new_mountpoint is
    safe to call.

Signed-off-by: Eric W. Biederman <ebiederman@twitter.com>
---
 fs/mount.h     |    2 ++
 fs/namespace.c |   39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 0 deletions(-)

diff --git a/fs/mount.h b/fs/mount.h
index 50a72d46e7a6..2b470f34e665 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -84,6 +84,8 @@ extern struct mount *__lookup_mnt_last(struct vfsmount *, struct dentry *);
 
 extern bool legitimize_mnt(struct vfsmount *, unsigned);
 
+extern void detach_mounts(struct dentry *dentry);
+
 static inline void get_mnt_ns(struct mnt_namespace *ns)
 {
 	atomic_inc(&ns->count);
diff --git a/fs/namespace.c b/fs/namespace.c
index 33db9e95bd5c..7abbf722ce18 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1359,6 +1359,45 @@ static int do_umount(struct mount *mnt, int flags)
 	return retval;
 }
 
+/*
+ * detach_mounts - lazily unmount all mounts on the specified dentry
+ *
+ * During unlink, rmdir, and d_drop it is possible to loose the path
+ * to an existing mountpoint, and wind up leaking the mount.
+ * detach_mounts allows lazily unmounting those mounts instead of
+ * leaking them.
+ * 
+ * The caller may hold dentry->d_inode->i_mutex.
+ */
+void detach_mounts(struct dentry *dentry)
+{
+	struct mountpoint *mp;
+	struct mount *mnt;
+
+	namespace_lock();
+	if (!d_mountpoint(dentry))
+		goto out_unlock;
+
+	/* 
+	 * The namespace lock and d_mountpoint being set guarantees
+	 * that new_mountpoint will just be a lookup of the existing
+	 * mountpoint structure.
+	 */
+	mp = new_mountpoint(dentry);
+	if (IS_ERR(mp))
+		goto out_unlock;
+
+	lock_mount_hash();
+	while (!list_empty(&mp->m_list)) {
+		mnt = list_first_entry(&mp->m_list, struct mount, mnt_mp_list);
+		umount_tree(mnt, 1);
+	}
+	unlock_mount_hash();
+	put_mountpoint(mp);
+out_unlock:
+	namespace_unlock();
+}
+
 /* 
  * Is the caller allowed to modify his namespace?
  */
-- 
1.7.5.4