From: Jan Kara <jack@suse.cz>
Date: Fri, 4 Oct 2013 13:29:12 +0000 (-0400)
Subject: IB/qib: Convert qib_user_sdma_pin_pages() to use get_user_pages_fast()
X-Git-Tag: v3.2.54~141
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=434700a29d1e1b0a31dd03dc8b5d0f5424a09bca;p=pandora-kernel.git

IB/qib: Convert qib_user_sdma_pin_pages() to use get_user_pages_fast()

commit 603e7729920e42b3c2f4dbfab9eef4878cb6e8fa upstream.

qib_user_sdma_queue_pkts() gets called with mmap_sem held for
writing. Except for get_user_pages() deep down in
qib_user_sdma_pin_pages() we don't seem to need mmap_sem at all.  Even
more interestingly the function qib_user_sdma_queue_pkts() (and also
qib_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 qib_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.

Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Roland Dreier <roland@purestorage.com>
[bwh: Backported to 3.2:
 - Adjust context
 - Adjust indentation and nr_pages argument in qib_user_sdma_pin_pages()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

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