nvme: lock NS list changes while handling command effects

If a controller supports the NS Change Notification, the namespace
scan_work is automatically triggered after attaching a new namespace.

Occasionally the namespace scan_work may append the new namespace to the
list before the admin command effects handling is completed. The effects
handling unfreezes namespaces, but if it unfreezes the newly attached
namespace, its request_queue freeze depth will be off and we'll hit the
warning in blk_mq_unfreeze_queue().

On the next namespace add, we will fail to freeze that queue due to the
previous bad accounting and deadlock waiting for frozen.

Fix that by preventing scan work from altering the namespace list while
command effects handling needs to pair freeze with unfreeze.
Reported-by: Wen Xiong <wenxiong@us.ibm.com>
Tested-by: Wen Xiong <wenxiong@us.ibm.com>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/core.c

@@ -1253,6 +1253,7 @@ static u32 nvme_passthru_start(struct nvme_ctrl *ctrl, struct nvme_ns *ns,
 	 * effects say only one namespace is affected.
 	 */
 	if (effects & (NVME_CMD_EFFECTS_LBCC | NVME_CMD_EFFECTS_CSE_MASK)) {
+		mutex_lock(&ctrl->scan_lock);
 		nvme_start_freeze(ctrl);
 		nvme_wait_freeze(ctrl);
 	}
@@ -1281,8 +1282,10 @@ static void nvme_passthru_end(struct nvme_ctrl *ctrl, u32 effects)
 	 */
 	if (effects & NVME_CMD_EFFECTS_LBCC)
 		nvme_update_formats(ctrl);
-	if (effects & (NVME_CMD_EFFECTS_LBCC | NVME_CMD_EFFECTS_CSE_MASK))
+	if (effects & (NVME_CMD_EFFECTS_LBCC | NVME_CMD_EFFECTS_CSE_MASK)) {
 		nvme_unfreeze(ctrl);
+		mutex_unlock(&ctrl->scan_lock);
+	}
 	if (effects & NVME_CMD_EFFECTS_CCC)
 		nvme_init_identify(ctrl);
 	if (effects & (NVME_CMD_EFFECTS_NIC | NVME_CMD_EFFECTS_NCC))
@@ -3401,6 +3404,7 @@ static void nvme_scan_work(struct work_struct *work)
 	if (nvme_identify_ctrl(ctrl, &id))
 		return;
 
+	mutex_lock(&ctrl->scan_lock);
 	nn = le32_to_cpu(id->nn);
 	if (ctrl->vs >= NVME_VS(1, 1, 0) &&
 	    !(ctrl->quirks & NVME_QUIRK_IDENTIFY_CNS)) {
@@ -3409,6 +3413,7 @@ static void nvme_scan_work(struct work_struct *work)
 	}
 	nvme_scan_ns_sequential(ctrl, nn);
 out_free_id:
+	mutex_unlock(&ctrl->scan_lock);
 	kfree(id);
 	down_write(&ctrl->namespaces_rwsem);
 	list_sort(NULL, &ctrl->namespaces, ns_cmp);
@@ -3652,6 +3657,7 @@ int nvme_init_ctrl(struct nvme_ctrl *ctrl, struct device *dev,
 
 	ctrl->state = NVME_CTRL_NEW;
 	spin_lock_init(&ctrl->lock);
+	mutex_init(&ctrl->scan_lock);
 	INIT_LIST_HEAD(&ctrl->namespaces);
 	init_rwsem(&ctrl->namespaces_rwsem);
 	ctrl->dev = dev;

drivers/nvme/host/nvme.h

@@ -154,6 +154,7 @@ struct nvme_ctrl {
 	enum nvme_ctrl_state state;
 	bool identified;
 	spinlock_t lock;
+	struct mutex scan_lock;
 	const struct nvme_ctrl_ops *ops;
 	struct request_queue *admin_q;
 	struct request_queue *connect_q;