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    Subject[patch 7/9] Locking rules for taking multiple mmap_sem locks.
    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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