From: Damien Le Moal damien.lemoal@opensource.wdc.com
commit 2820e5d0820ac4daedff1272616a53d9c7682fd2 upstream.
dd_finish_request() tests if the per prio fifo_list is not empty to determine if request dispatching must be restarted for handling blocked write requests to zoned devices with a call to blk_mq_sched_mark_restart_hctx(). While simple, this implementation has 2 problems:
1) Only the priority level of the completed request is considered. However, writes to a zone may be blocked due to other writes to the same zone using a different priority level. While this is unlikely to happen in practice, as writing a zone with different IO priorirites does not make sense, nothing in the code prevents this from happening. 2) The use of list_empty() is dangerous as dd_finish_request() does not take dd->lock and may run concurrently with the insert and dispatch code.
Fix these 2 problems by testing the write fifo list of all priority levels using the new helper dd_has_write_work(), and by testing each fifo list using list_empty_careful().
Fixes: c807ab520fc3 ("block/mq-deadline: Add I/O priority support") Cc: stable@vger.kernel.org Signed-off-by: Damien Le Moal damien.lemoal@opensource.wdc.com Reviewed-by: Johannes Thumshirn johannes.thumshirn@wdc.com Link: https://lore.kernel.org/r/20221124021208.242541-2-damien.lemoal@opensource.w... Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- block/mq-deadline.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-)
--- a/block/mq-deadline.c +++ b/block/mq-deadline.c @@ -789,6 +789,18 @@ static void dd_prepare_request(struct re rq->elv.priv[0] = NULL; }
+static bool dd_has_write_work(struct blk_mq_hw_ctx *hctx) +{ + struct deadline_data *dd = hctx->queue->elevator->elevator_data; + enum dd_prio p; + + for (p = 0; p <= DD_PRIO_MAX; p++) + if (!list_empty_careful(&dd->per_prio[p].fifo_list[DD_WRITE])) + return true; + + return false; +} + /* * Callback from inside blk_mq_free_request(). * @@ -828,9 +840,10 @@ static void dd_finish_request(struct req
spin_lock_irqsave(&dd->zone_lock, flags); blk_req_zone_write_unlock(rq); - if (!list_empty(&per_prio->fifo_list[DD_WRITE])) - blk_mq_sched_mark_restart_hctx(rq->mq_hctx); spin_unlock_irqrestore(&dd->zone_lock, flags); + + if (dd_has_write_work(rq->mq_hctx)) + blk_mq_sched_mark_restart_hctx(rq->mq_hctx); } }