UBUNTU: SAUCE: Fix non-prefaulted page deadlock (LP: #1754584)

UBUNTU: SAUCE: Fix non-prefaulted page deadlock (LP: #1754584)

BugLink: https://bugs.launchpad.net/bugs/1754584
Fix mmap'd libaio read on non-prefaulted page deadlock. This is a hot fix
from ZFS upstream that ensure pages do not deadlock.

Performing a read with the target data in a mmap'd page that is map'd into
the same blocks that are being read causes a lock on the page and a further
lock on the same page when the page is being faulted in, causing deadlock.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>