From: Josef Bacik <jo...@toxicpanda.com> 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. Reviewed-by: Oleg Nesterov <o...@redhat.com> Signed-off-by: Josef Bacik <jo...@toxicpanda.com> Signed-off-by: Jens Axboe <ax...@kernel.dk> Changes when porting to vz7: - original patch is patching block/blk-rq-qos.c:rq_qos_wait, but in vz7 similar hunk is in block/blk-wbt.c:__wbt_wait https://jira.sw.ru/browse/PSBM-141883 (cherry picked from commit 545fbd0775bafcefc8f7bc844291bd13c44b7fdc) Signed-off-by: Pavel Tikhomirov <ptikhomi...@virtuozzo.com> --- block/blk-wbt.c | 1 + 1 file changed, 1 insertion(+) diff --git a/block/blk-wbt.c b/block/blk-wbt.c index 49d11e089c97..5477c3ffe7a7 100644 --- a/block/blk-wbt.c +++ b/block/blk-wbt.c @@ -571,6 +571,7 @@ static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct, 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; -- 2.37.1 _______________________________________________ Devel mailing list Devel@openvz.org https://lists.openvz.org/mailman/listinfo/devel
