[PATCH v3] nvmet: force reconnect when number of queue changes

[Daniel Wagner <dwagner@suse.de>]

In order to test queue number changes we need to make sure that the
host reconnects. Because only when the host disconnects from the
target the number of queues are allowed to change according the spec.

The initial idea was to disable and re-enable the ports and have the
host wait until the KATO timer expires, triggering error
recovery. Though the host would see a DNR reply when trying to
reconnect. Because of the DNR bit the connection is dropped
completely. There is no point in trying to reconnect with the same
parameters according the spec.

We can force to reconnect the host is by deleting all controllers. The
host will observe any newly posted request to fail and thus starts the
error recovery but this time without the DNR bit set.

Also, the item passed into nvmet_subsys_attr_qid_max_show is not a
member of struct nvmet_port, it is part of nvmet_subsys. Hence,
don't try to dereference it as struct nvme_ctrl pointer.

Fixes: 3e980f5995e0 ("nvmet: Expose max queues to configfs")
Reported-by: Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Link: https://lore.kernel.org/r/20220913064203.133536-1-dwagner@suse.de
Signed-off-by: Daniel Wagner <dwagner@suse.de>
---
v3:
  - Updated Fixes tag
  - Updated commit message with some additional information
    from the v2 discussion

v2:
  - instead preventing changes, force reconnect by delete ctrls
  - renamed patch
  - https://lore.kernel.org/linux-nvme/20220927143157.3659-1-dwagner@suse.de/

v1:
  - initial verison
  - https://lore.kernel.org/linux-nvme/20220913064203.133536-1-dwagner@suse.de/

 drivers/nvme/target/configfs.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/nvme/target/configfs.c b/drivers/nvme/target/configfs.c
index e34a2896fedb..051a420d818e 100644
--- a/drivers/nvme/target/configfs.c
+++ b/drivers/nvme/target/configfs.c
@@ -1290,12 +1290,10 @@ static ssize_t nvmet_subsys_attr_qid_max_show(struct config_item *item,
 static ssize_t nvmet_subsys_attr_qid_max_store(struct config_item *item,
 					       const char *page, size_t cnt)
 {
-	struct nvmet_port *port = to_nvmet_port(item);
+	struct nvmet_subsys *subsys = to_subsys(item);
+	struct nvmet_ctrl *ctrl;
 	u16 qid_max;
 
-	if (nvmet_is_port_enabled(port, __func__))
-		return -EACCES;
-
 	if (sscanf(page, "%hu\n", &qid_max) != 1)
 		return -EINVAL;
 
@@ -1303,8 +1301,13 @@ static ssize_t nvmet_subsys_attr_qid_max_store(struct config_item *item,
 		return -EINVAL;
 
 	down_write(&nvmet_config_sem);
-	to_subsys(item)->max_qid = qid_max;
+	subsys->max_qid = qid_max;
+
+	/* Force reconnect */
+	list_for_each_entry(ctrl, &subsys->ctrls, subsys_entry)
+		ctrl->ops->delete_ctrl(ctrl);
 	up_write(&nvmet_config_sem);
+
 	return cnt;
 }
 CONFIGFS_ATTR(nvmet_subsys_, attr_qid_max);
-- 
2.37.3