vfs: remove dentry of an unliked file from dentry cache

If dentry has elevated reference count during unlink (a file is opened
for instance) it is not destroyed and remains in the dentry hash.
As a result unlinked file is still accessible.

Signed-off-by: Gleb Natapov <gleb@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>

fs/vfs/vfs_syscalls.cc

@@ -839,6 +839,7 @@ sys_unlink(char *path)
 	vn_unlock(ddp->d_vnode);
 
 	vn_unlock(vp);
+	dentry_remove(dp);
 	drele(ddp);
 	drele(dp);
 	return 0;