[PATCH v2 1/2] blk-mq: add tagset quiesce interface

[Christoph Hellwig]

On Tue, Oct 18, 2022 at 11:39:30AM +0300, Sagi Grimberg wrote:
> The only question in my mind is regarding patch 2/2 with the subtle
> ordering of nvme_set_queue_dying...

I think we need to sort that out as a pre-patch.  There is quite some
history there was a fair amount of dead lock potential earlier, but
I think I sorted quite a lot out there, including a new lock for setting
the gendisk size, which is what the comment refers to.

Something like this:

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 059737c1a2c19..cb7623b5d2c8b 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -5105,21 +5105,21 @@ static void nvme_stop_ns_queue(struct nvme_ns *ns)
 
 /*
  * Prepare a queue for teardown.
- *
- * This must forcibly unquiesce queues to avoid blocking dispatch, and only set
- * the capacity to 0 after that to avoid blocking dispatchers that may be
- * holding bd_butex.  This will end buffered writers dirtying pages that can't
- * be synced.
  */
 static void nvme_set_queue_dying(struct nvme_ns *ns)
 {
 	if (test_and_set_bit(NVME_NS_DEAD, &ns->flags))
 		return;
 
+	/*
+	 * Mark the disk dead to prevent new opens, and set the capacity to 0
+	 * to end buffered writers dirtying pages that can't be synced.
+	 */
 	blk_mark_disk_dead(ns->disk);
-	nvme_start_ns_queue(ns);
-
 	set_capacity_and_notify(ns->disk, 0);
+
+	/* forcibly unquiesce queues to avoid blocking dispatch */
+	nvme_start_ns_queue(ns);
 }
 
 /**