| Message ID | 20190716201929.79142-3-josef@toxicpanda.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | rq-qos memory barrier shenanigans | expand |
diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c index 659ccb8b693f..67a0a4c07060 100644 --- a/block/blk-rq-qos.c +++ b/block/blk-rq-qos.c @@ -244,6 +244,7 @@ void rq_qos_wait(struct rq_wait *rqw, void *private_data, return; prepare_to_wait_exclusive(&rqw->wait, &data.wq, TASK_UNINTERRUPTIBLE); + has_sleeper = !wq_has_single_sleeper(&rqw->wait); do { if (data.got_token) break;
We saw a hang in production with WBT where there was only one waiter in the throttle path and no outstanding IO. This is because of the has_sleepers optimization that is used to make sure we don't steal an inflight counter for new submitters when there are people already on the list. We can race with our check to see if the waitqueue has any waiters (this is done locklessly) and the time we actually add ourselves to the waitqueue. If this happens we'll go to sleep and never be woken up because nobody is doing IO to wake us up. Fix this by checking if the waitqueue has a single sleeper on the list after we add ourselves, that way we have an uptodate view of the list. Signed-off-by: Josef Bacik <josef@toxicpanda.com> --- block/blk-rq-qos.c | 1 + 1 file changed, 1 insertion(+)