[PATCH 2/4] ublk: drop QUIESCE_DEV's wait for an idle command

[Josef Bacik]

ublk_wait_for_idle_io() is meant to wait until every queue has a command
whose request is not with the server, so that canceling it tells the
server about the quiesce. It never waits: blk_mq_tagset_busy_iter()
only calls ublk_count_busy_req() for started requests, and the callback
counts a request only when it is not started, so nr_busy is always 0
and every queue looks idle.

Making it count would not help either. It runs with ub->mutex held, so
a server which keeps every tag busy would hold up STOP_DEV, recovery
and its own release work for as long as the QUIESCE_DEV timeout, which
is forever by default. Drop it; nothing changes, since it never waited,
and a later patch has QUIESCE_DEV keep canceling until the server has
been told, without ub->mutex held.

The QUIESCE_DEV timeout in data[0] is unused until then.

Fixes: b465ae7b2524 ("ublk: add feature UBLK_F_QUIESCE")
Assisted-by: LLM
Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
---
 drivers/block/ublk_drv.c | 75 ----------------------------------------
 1 file changed, 75 deletions(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 0bd0b95b3217..bd7126dcf92f 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -5338,80 +5338,9 @@ static int ublk_ctrl_set_size(struct ublk_device *ub, const struct ublksrv_ctrl_
 	return ret;
 }
 
-struct count_busy {
-	const struct ublk_queue *ubq;
-	u16 nr_busy;
-};
-
-static bool ublk_count_busy_req(struct request *rq, void *data)
-{
-	struct count_busy *idle = data;
-
-	if (!blk_mq_request_started(rq) && rq->mq_hctx->driver_data == idle->ubq)
-		idle->nr_busy += 1;
-	return true;
-}
-
-/* uring_cmd is guaranteed to be active if the associated request is idle */
-static bool ubq_has_idle_io(const struct ublk_queue *ubq)
-{
-	struct count_busy data = {
-		.ubq = ubq,
-	};
-
-	blk_mq_tagset_busy_iter(&ubq->dev->tag_set, ublk_count_busy_req, &data);
-	return data.nr_busy < ubq->q_depth;
-}
-
-/* Wait until each hw queue has at least one idle IO */
-static int ublk_wait_for_idle_io(struct ublk_device *ub,
-				 unsigned int timeout_ms)
-{
-	unsigned int elapsed = 0;
-	int ret;
-
-	/*
-	 * For UBLK_F_BATCH_IO ublk server can get notified with existing
-	 * or new fetch command, so needn't wait any more
-	 */
-	if (ublk_dev_support_batch_io(ub))
-		return 0;
-
-	while (elapsed < timeout_ms && !signal_pending(current)) {
-		u16 i, queues_cancelable = 0;
-
-		for (i = 0; i < ub->dev_info.nr_hw_queues; i++) {
-			struct ublk_queue *ubq = ublk_get_queue(ub, i);
-
-			queues_cancelable += !!ubq_has_idle_io(ubq);
-		}
-
-		/*
-		 * Each queue needs at least one active command for
-		 * notifying ublk server
-		 */
-		if (queues_cancelable == ub->dev_info.nr_hw_queues)
-			break;
-
-		msleep(UBLK_REQUEUE_DELAY_MS);
-		elapsed += UBLK_REQUEUE_DELAY_MS;
-	}
-
-	if (signal_pending(current))
-		ret = -EINTR;
-	else if (elapsed >= timeout_ms)
-		ret = -EBUSY;
-	else
-		ret = 0;
-
-	return ret;
-}
-
 static int ublk_ctrl_quiesce_dev(struct ublk_device *ub,
 				 const struct ublksrv_ctrl_cmd *header)
 {
-	/* zero means wait forever */
-	u64 timeout_ms = header->data[0];
 	struct gendisk *disk;
 	bool live = true;
 	int ret = -ENODEV;
@@ -5445,10 +5374,6 @@ static int ublk_ctrl_quiesce_dev(struct ublk_device *ub,
 	blk_mq_unquiesce_queue(disk->queue);
 	mutex_unlock(&ub->cancel_mutex);
 
-	if (!timeout_ms)
-		timeout_ms = UINT_MAX;
-	ret = ublk_wait_for_idle_io(ub, timeout_ms);
-
 put_disk:
 	ublk_put_disk(disk);
 unlock:
-- 
2.55.0