block: fix deadline elevator drain for zoned block devices

When the deadline scheduler is used with a zoned block device, writes
to a zone will be dispatched one at a time. This causes the warning
message:

deadline: forced dispatching is broken (nr_sorted=X), please report this

to be displayed when switching to another elevator with the legacy I/O
path while write requests to a zone are being retained in the scheduler
queue.

Prevent this message from being displayed when executing
elv_drain_elevator() for a zoned block device. __blk_drain_queue() will
loop until all writes are dispatched and completed, resulting in the
desired elevator queue drain without extensive modifications to the
deadline code itself to handle forced-dispatch calls.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Fixes: 8dc8146f9c92 ("deadline-iosched: Introduce zone locking support")
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/elevator.c b/block/elevator.c
index 6a06b5d..fae58b2 100644 (file)
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -609,7 +609,7 @@ void elv_drain_elevator(struct request_queue *q)
 
        while (e->type->ops.sq.elevator_dispatch_fn(q, 1))
                ;
-       if (q->nr_sorted && printed++ < 10) {
+       if (q->nr_sorted && !blk_queue_is_zoned(q) && printed++ < 10 ) {
                printk(KERN_ERR "%s: forced dispatching is broken "
                       "(nr_sorted=%u), please report this\n",
                       q->elevator->type->elevator_name, q->nr_sorted);