| Message ID | 20190710195227.92322-2-josef@toxicpanda.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/2] wait: add wq_has_multiple_sleepers helper | expand |
diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c index 659ccb8b693f..b39b5f3fb01b 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_multiple_sleepers(&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 multiple sleepers after we add ourselves to the list, 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(+)