[PATCH 01/12] ovl: use is_subdir() for testing if one thing is a subdir of another

[NeilBrown <neil@brown.name>]

Rather than using lock_rename(), use the more obvious is_subdir() for
ensuring that neither upper nor workdir contain the other.
Also be explicit in the comment that the two directories cannot be the
same.

Signed-off-by: NeilBrown <neil@brown.name>
---
 fs/overlayfs/super.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index cf99b276fdfb..db046b0d6a68 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -438,18 +438,12 @@ static int ovl_lower_dir(const char *name, struct path *path,
 	return 0;
 }
 
-/* Workdir should not be subdir of upperdir and vice versa */
+/* Workdir should not be subdir of upperdir and vice versa, and
+ * they should not be the same.
+ */
 static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
 {
-	bool ok = false;
-
-	if (workdir != upperdir) {
-		struct dentry *trap = lock_rename(workdir, upperdir);
-		if (!IS_ERR(trap))
-			unlock_rename(workdir, upperdir);
-		ok = (trap == NULL);
-	}
-	return ok;
+	return !is_subdir(workdir, upperdir) && !is_subdir(upperdir, workdir);
 }
 
 static int ovl_setup_trap(struct super_block *sb, struct dentry *dir,
-- 
2.49.0