[PATCH] nvme: core: freeze multipath queue early in nvme_update_ns_info()

[Martin Wilck]

For multipath devices, nvme_update_ns_info() needs to freeze both
the queue of the path and the queue of the multipath device. For
both operations, it waits for one RCU grace period to pass, ~25ms
on my test system. By calling blk_freeze_queue_start() for the
multipath queue early, we avoid waiting twice; tests using ftrace
have shown that the second blk_mq_freeze_queue_wait() call finishes
in just a few microseconds. The path queue is unfrozen before
calling blk_mq_freeze_queue_wait() on the multipath queue, so that
possibly outstanding IO in the multipath queue can be flushed.

I tested this using the "controller rescan under I/O load" test
I submitted recently [1].

[1] https://lore.kernel.org/linux-nvme/20240822193814.106111-3-mwilck@suse.com/T/#u

Signed-off-by: Martin Wilck <mwilck at suse.com>
---
 drivers/nvme/host/core.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 33fa01c599ad..e2454398c660 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -2217,6 +2217,9 @@ static int nvme_update_ns_info(struct nvme_ns *ns, struct nvme_ns_info *info)
 	bool unsupported = false;
 	int ret;
 
+	if (nvme_ns_head_multipath(ns->head))
+		blk_freeze_queue_start(ns->head->disk->queue);
+
 	switch (info->ids.csi) {
 	case NVME_CSI_ZNS:
 		if (!IS_ENABLED(CONFIG_BLK_DEV_ZONED)) {
@@ -2254,7 +2257,7 @@ static int nvme_update_ns_info(struct nvme_ns *ns, struct nvme_ns_info *info)
 		struct queue_limits *ns_lim = &ns->disk->queue->limits;
 		struct queue_limits lim;
 
-		blk_mq_freeze_queue(ns->head->disk->queue);
+		blk_mq_freeze_queue_wait(ns->head->disk->queue);
 		/*
 		 * queue_limits mixes values that are the hardware limitations
 		 * for bio splitting with what is the device configuration.
@@ -2288,7 +2291,8 @@ static int nvme_update_ns_info(struct nvme_ns *ns, struct nvme_ns_info *info)
 		nvme_mpath_revalidate_paths(ns);
 
 		blk_mq_unfreeze_queue(ns->head->disk->queue);
-	}
+	} else if (nvme_ns_head_multipath(ns->head))
+		blk_mq_unfreeze_queue(ns->head->disk->queue);
 
 	return ret;
 }
-- 
2.35.3