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Subject: [PATCH 11 of 11] mmap sems
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Date: Fri, 02 May 2008 17:05:14 +0200
From: Andrea Arcangeli <andrea@qumranet.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Lameter <clameter@sgi.com>, Jack Steiner <steiner@sgi.com>,
       Robin Holt <holt@sgi.com>, Nick Piggin <npiggin@suse.de>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       kvm-devel@lists.sourceforge.net, Kanoj Sarcar <kanojsarcar@yahoo.com>,
       Roland Dreier <rdreier@cisco.com>,
       Steve Wise <swise@opengridcomputing.com>, linux-kernel@vger.kernel.org,
       Avi Kivity <avi@qumranet.com>, linux-mm@kvack.org,
       general@lists.openfabrics.org, Hugh Dickins <hugh@veritas.com>,
       akpm@linux-foundation.org, Rusty Russell <rusty@rustcorp.com.au>,
       Anthony Liguori <aliguori@us.ibm.com>, Chris Wright <chrisw@redhat.com>,
       Marcelo Tosatti <marcelo@kvack.org>, Eric Dumazet <dada1@cosmosbay.com>,
       "Paul E. McKenney" <paulmck@us.ibm.com>
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# 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)