tree e73fa24015b0a494fbe9dab8a1e9b3460c935b87
parent d8f429e1669b9709f5b669aac9d734dbe0640891
author Jens Axboe <axboe@fb.com> 1412692760 -0600
committer Jens Axboe <axboe@fb.com> 1412692760 -0600

blk-mq: fix potential hang if rolling wakeup depth is too high

We currently divide the queue depth by 4 as our batch wakeup
count, but we split the wakeups over BT_WAIT_QUEUES number of
wait queues. This defaults to 8. If the product of the resulting
batch wake count and BT_WAIT_QUEUES is higher than the device
queue depth, we can get into a situation where a task goes to
sleep waiting for a request, but never gets woken up.

Reported-by: Bart Van Assche <bvanassche@acm.org>
Fixes: 4bb659b156996
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <axboe@fb.com>