IB/qib: Convert qib_user_sdma_pin_pages() to use get_user_pages_fast()
authorJan Kara <jack@suse.cz>
Fri, 4 Oct 2013 13:29:12 +0000 (09:29 -0400)
committerRoland Dreier <roland@purestorage.com>
Fri, 8 Nov 2013 22:43:11 +0000 (14:43 -0800)
commit603e7729920e42b3c2f4dbfab9eef4878cb6e8fa
tree447d2329598d102375c38230f01396662ef57443
parent4adcf7fb6783e354aab38824d803fa8c4f8e8a27
IB/qib: Convert qib_user_sdma_pin_pages() to use get_user_pages_fast()

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.

Cc: <stable@vger.kernel.org>
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Roland Dreier <roland@purestorage.com>
drivers/infiniband/hw/qib/qib_user_sdma.c