From 0ecfc95da4f159e3a773bf1c0554e5f064bda491 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Fri, 4 Oct 2013 09:29:06 -0400
Subject: [PATCH] IB/ipath: Convert ipath_user_sdma_pin_pages() to use
 get_user_pages_fast()

commit 4adcf7fb6783e354aab38824d803fa8c4f8e8a27 upstream.

ipath_user_sdma_queue_pkts() gets called with mmap_sem held for
writing.  Except for get_user_pages() deep down in
ipath_user_sdma_pin_pages() we don't seem to need mmap_sem at all.

Even more interestingly the function ipath_user_sdma_queue_pkts() (and
also ipath_user_sdma_coalesce() called somewhat later) call
copy_from_user() which can hit a page fault and we deadlock on trying
to get mmap_sem when handling that fault.  So just make
ipath_user_sdma_pin_pages() use get_user_pages_fast() and leave
mmap_sem locking for mm.

This deadlock has actually been observed in the wild when the node
is under memory pressure.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>

[ Merged in fix for call to get_user_pages_fast from Tetsuo Handa
  <penguin-kernel@I-love.SAKURA.ne.jp>.  - Roland ]

Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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