[PATCH 11 of 11] mmap sems

[Andrea Arcangeli]

# HG changeset patch
# User Andrea Arcangeli <andrea@xxxxxxxxxxxx>
# 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@xxxxxxx>
Signed-off-by: Andrea Arcangeli <andrea@xxxxxxxxxxxx>

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)
--
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