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: <[email protected]>
Reviewed-by: Mike Marciniszyn <[email protected]>
Signed-off-by: Jan Kara <[email protected]>
Signed-off-by: Roland Dreier <[email protected]>

0 files changed, 0 insertions, 0 deletions