ovl: narrow locking in ovl_cleanup_whiteouts()

Rather than lock the directory for the whole operation, use
ovl_lookup_upper_unlocked() and ovl_cleanup_unlocked() to take the lock
only when needed.

This makes way for future changes where locks are taken on individual
dentries rather than the whole directory.

Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: NeilBrown <neil@brown.name>
Link: https://lore.kernel.org/20250716004725.1206467-11-neil@brown.name
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: neilbrown

fs/overlayfs/readdir.c

@@ -1034,25 +1034,23 @@ void ovl_cleanup_whiteouts(struct ovl_fs *ofs, struct dentry *upper,
 {
 	struct ovl_cache_entry *p;
 
-	inode_lock_nested(upper->d_inode, I_MUTEX_CHILD);
 	list_for_each_entry(p, list, l_node) {
 		struct dentry *dentry;
 
 		if (WARN_ON(!p->is_whiteout || !p->is_upper))
 			continue;
 
-		dentry = ovl_lookup_upper(ofs, p->name, upper, p->len);
+		dentry = ovl_lookup_upper_unlocked(ofs, p->name, upper, p->len);
 		if (IS_ERR(dentry)) {
 			pr_err("lookup '%s/%.*s' failed (%i)\n",
 			       upper->d_name.name, p->len, p->name,
 			       (int) PTR_ERR(dentry));
 			continue;
 		}
 		if (dentry->d_inode)
-			ovl_cleanup(ofs, upper->d_inode, dentry);
+			ovl_cleanup_unlocked(ofs, upper, dentry);
 		dput(dentry);
 	}
-	inode_unlock(upper->d_inode);
 }
 
 static bool ovl_check_d_type(struct dir_context *ctx, const char *name,