[REVIEW][PATCH 1/2] mnt: Fix propagate_mount_busy to notice all cases of busy mounts.

[ebiederm@xmission.com (Eric W. Biederman)]

When I look at what propagate_mount_busy is trying to do and I look
at the code closely I discover there is a great disconnect between the
two.  In the ordinary non-propagation case propagate_mount_busy has
been verifying that there are no submounts and that there are no
extraneous references on the mount.

For mounts that the unmount would propagate to propagate_mount_busy has
been verifying that there are no extraneous references only if there
are no submounts.  Which is nonsense.

Thefore rework the logic in propgate_mount_busy so that for each
mount it examines it considers that mount busy if that mount has
children or if there are extraneous references to that mount.

While this check was incorrect we could leak mounts instead of simply
failing umount.

Cc: stable@vger.kernel.org
Fixes: a05964f3917c ("[PATCH] shared mounts handling: umount")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---

If you don't figure this fix is worth it after all of this time please
let me know.  This feels like the proper thing to do, and I don't expect
it will break anyone to fix this.

 fs/pnode.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/fs/pnode.c b/fs/pnode.c
index 06a793f4ae38..12fafa711114 100644
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -344,7 +344,6 @@ int propagate_mount_busy(struct mount *mnt, int refcnt)
 {
 	struct mount *m, *child;
 	struct mount *parent = mnt->mnt_parent;
-	int ret = 0;
 
 	if (mnt == parent)
 		return do_refcount_check(mnt, refcnt);
@@ -360,11 +359,13 @@ int propagate_mount_busy(struct mount *mnt, int refcnt)
 	for (m = propagation_next(parent, parent); m;
 	     		m = propagation_next(m, parent)) {
 		child = __lookup_mnt_last(&m->mnt, mnt->mnt_mountpoint);
-		if (child && list_empty(&child->mnt_mounts) &&
-		    (ret = do_refcount_check(child, 1)))
-			break;
+		if (!child)
+			continue;
+		if (!list_empty(&child->mnt_mounts) ||
+		    do_refcount_check(child, 1))
+			return 1;
 	}
-	return ret;
+	return 0;
 }
 
 /*
-- 
2.10.1