linux-kernel - [PATCH 11 of 11] mmap sems

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Date:	Fri, 02 May 2008 17:05:14 +0200
From:	Andrea Arcangeli <andrea@...ranet.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Christoph Lameter <clameter@....com>,
	Jack Steiner <steiner@....com>, Robin Holt <holt@....com>,
	Nick Piggin <npiggin@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	kvm-devel@...ts.sourceforge.net,
	Kanoj Sarcar <kanojsarcar@...oo.com>,
	Roland Dreier <rdreier@...co.com>,
	Steve Wise <swise@...ngridcomputing.com>,
	linux-kernel@...r.kernel.org, Avi Kivity <avi@...ranet.com>,
	linux-mm@...ck.org, general@...ts.openfabrics.org,
	Hugh Dickins <hugh@...itas.com>, akpm@...ux-foundation.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Anthony Liguori <aliguori@...ibm.com>,
	Chris Wright <chrisw@...hat.com>,
	Marcelo Tosatti <marcelo@...ck.org>,
	Eric Dumazet <dada1@...mosbay.com>,
	"Paul E. McKenney" <paulmck@...ibm.com>
Subject: [PATCH 11 of 11] mmap sems

# HG changeset patch
# User Andrea Arcangeli <andrea@...ranet.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@....com>
Signed-off-by: Andrea Arcangeli <andrea@...ranet.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)
--
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