[PATCH 11 of 11] mmap sems

Andrea Arcangeli
2008-05-02T15:17:42Z

# HG changeset patch
# User Andrea Arcangeli <andrea@qumranet.com>
# Date 1209740229 -7200
# Node ID b4bf6df98bc00bfbef9423b0dd31cfdba63a5eeb
# Parent 4f462fb3dff614cd7d971219c3feaef0b43359c1
mmap sems

This patch adds a lock ordering rule to avoid a potential deadlock when
multiple mmap_sems need to be locked.

Signed-off-by: Dean Nelson <dcn@sgi.com>
Signed-off-by: Andrea Arcangeli <andrea@qumranet.com>

diff --git a/mm/filemap.c b/mm/filemap.c
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -79,6 +79,9 @@ generic_file_direct_IO(int rw, struct ki
*
* ->i_mutex (generic_file_buffered_write)
* ->mmap_sem (fault_in_pages_readable->do_page_fault)
+ *
+ * When taking multiple mmap_sems, one should lock the lowest-addressed
+ * one first proceeding on up to the highest-addressed one.
*
* ->i_mutex
* ->i_alloc_sem (various)