[PATCH 3/4] nvmet: prevent max_qid changes for discovered subsystems

[Max Gurtovoy]

Disallow updates to the max_qid attribute via configfs after a
subsystem has been discovered. This prevents invalid configuration
and avoids races during controller setup. The maximal queue
identifier can now only be set on non-discovered subsystems,
ensuring consistent configuration state.

Signed-off-by: Max Gurtovoy <mgurtovoy at nvidia.com>
---
 drivers/nvme/target/configfs.c | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/drivers/nvme/target/configfs.c b/drivers/nvme/target/configfs.c
index 979eb184756a..ac12326e036c 100644
--- a/drivers/nvme/target/configfs.c
+++ b/drivers/nvme/target/configfs.c
@@ -1673,12 +1673,27 @@ static ssize_t nvmet_subsys_attr_qid_max_show(struct config_item *item,
 	return snprintf(page, PAGE_SIZE, "%u\n", to_subsys(item)->max_qid);
 }
 
+static ssize_t
+nvmet_subsys_attr_qid_max_store_locked(struct nvmet_subsys *subsys,
+		u16 qid_max, size_t cnt)
+{
+	if (subsys->subsys_discovered) {
+		pr_err("Can't set maximal qid. %u is already assigned\n",
+		       subsys->max_qid);
+		return -EINVAL;
+	}
+
+	subsys->max_qid = qid_max;
+
+	return cnt;
+}
+
 static ssize_t nvmet_subsys_attr_qid_max_store(struct config_item *item,
 					       const char *page, size_t cnt)
 {
 	struct nvmet_subsys *subsys = to_subsys(item);
-	struct nvmet_ctrl *ctrl;
 	u16 qid_max;
+	ssize_t ret;
 
 	if (sscanf(page, "%hu\n", &qid_max) != 1)
 		return -EINVAL;
@@ -1687,14 +1702,12 @@ static ssize_t nvmet_subsys_attr_qid_max_store(struct config_item *item,
 		return -EINVAL;
 
 	down_write(&nvmet_config_sem);
-	subsys->max_qid = qid_max;
-
-	/* Force reconnect */
-	list_for_each_entry(ctrl, &subsys->ctrls, subsys_entry)
-		ctrl->ops->delete_ctrl(ctrl);
+	mutex_lock(&subsys->lock);
+	ret = nvmet_subsys_attr_qid_max_store_locked(subsys, qid_max, cnt);
+	mutex_unlock(&subsys->lock);
 	up_write(&nvmet_config_sem);
 
-	return cnt;
+	return ret;
 }
 CONFIGFS_ATTR(nvmet_subsys_, attr_qid_max);
 
-- 
2.18.1