If the requested I/O scheduler is already in place, elevator_switch simply
leaves the queue alone, and returns.  However, it forgets to call
elevator_put, so

'echo [current_sched] > /sys/block/[dev]/queue/scheduler'

will leak a reference, causing the current_sched module to be permanently
pinned in memory.

Signed-off-by: Nate Diller <nate@namesys.com>
Acked-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>