This reverts commit 76d697d1.

The commit 76d697d1 causes general protection fault
reported from Bart Van Assche:

	https://lkml.org/lkml/2015/1/28/334Reported-by: NBart Van Assche <bart.vanassche@sandisk.com>
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>