locking rules:
-========== ============= ================= =========
+====================== ============= ================= =========
ops inode->i_lock blocked_lock_lock may block
-========== ============= ================= =========
+====================== ============= ================= =========
lm_notify: yes yes no
lm_grant: no no no
lm_break: yes no no
lm_change yes no no
lm_breaker_owns_lease: no no no
-========== ============= ================= =========
+====================== ============= ================= =========
buffer_head
===========
locking rules:
-============= ======== ===========================
+============= ========= ===========================
ops mmap_lock PageLocked(page)
-============= ======== ===========================
+============= ========= ===========================
open: yes
close: yes
fault: yes can return with page locked
page_mkwrite: yes can return with page locked
pfn_mkwrite: yes
access: yes
-============= ======== ===========================
+============= ========= ===========================
->fault() is called when a previously not present pte is about
to be faulted in. The filesystem must find and return the page associated