[ofa-general] [PATCH 12 of 12] This patch adds a lock ordering rule to avoid a potential deadlock when

[Andrea Arcangeli]

# HG changeset patch
# User Andrea Arcangeli <andrea at qumranet.com>
# Date 1208872187 -7200
# Node ID e847039ee2e815088661933b7195584847dc7540
# Parent  128d705f38c8a774ac11559db445787ce6e91c77
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 at sgi.com>

diff --git a/mm/filemap.c b/mm/filemap.c
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -79,6 +79,9 @@
  *
  *  ->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)