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@xxxxxxxxxxxxxxx>
Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>
---
block/mq-deadline.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index 5639921dfa92..36374481cb87 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -789,6 +789,18 @@ static void dd_prepare_request(struct request *rq)
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 request *rq)
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);
}
}
--
2.38.1
