- lock = cl_lock_request(env, io, descr, CEF_ASYNC,
- "glimpse", cfs_current());
+ /*
+ * CEF_ASYNC is used because glimpse sub-locks cannot
+ * deadlock (because they never conflict with other
+ * locks) and, hence, can be enqueued out-of-order.
+ *
+ * CEF_MUST protects glimpse lock from conversion into
+ * a lockless mode.
+ */
+ lock = cl_lock_request(env, io, descr, "glimpse",
+ cfs_current());