[PATCH 38/41] union-mount: Make pivot_root work with union mounts

[Valerie Aurora]

When moving a union mount, follow it down to the bottom layer and move
that instead of just the top layer.

Signed-off-by: Valerie Aurora <vaurora@xxxxxxxxxx>
---
 fs/namespace.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 9b71743..6ac5fc1 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2282,6 +2282,15 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
 	if (d_unlinked(old.dentry))
 		goto out2;
 	error = -EBUSY;
+	/*
+	 * follow_union_down() only goes one layer down.  We want the
+	 * bottom-most layer here - if we move that around, all the
+	 * layers on top move with it.  But if we ever allow more than
+	 * two layers, the below two will both need to be in while()
+	 * loops.
+	 */
+	follow_union_down(&new.mnt, &new.dentry);
+	follow_union_down(&root.mnt, &root.dentry);
 	if (new.mnt == root.mnt ||
 	    old.mnt == root.mnt)
 		goto out2; /* loop, on the same file system  */
-- 
1.6.3.3

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