[patch 08/10] xpmem: Locking rules for taking multiple mmap_sem locks.

[Christoph Lameter <clameter@sgi.com>]

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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>

---
 mm/filemap.c |    3 +++
 1 file changed, 3 insertions(+)

Index: linux-2.6/mm/filemap.c
===================================================================
--- linux-2.6.orig/mm/filemap.c	2008-04-01 13:02:41.374608387 -0700
+++ linux-2.6/mm/filemap.c	2008-04-01 13:05:02.777015782 -0700
@@ -80,6 +80,9 @@ 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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