nvme: fix use after free when disconnecting a reconnecting ctrl

A crash happens when trying to disconnect a reconnecting ctrl:

 1) The network was cut off when the connection was just established,
    scan work hang there waiting for some IOs complete.  Those I/Os were
    retried because we return BLK_STS_RESOURCE to blk in reconnecting.
 2) After a while, I tried to disconnect this connection.  This
    procedure also hangs because it tried to obtain ctrl->scan_lock.
    It should be noted that now we have switched the controller state
    to NVME_CTRL_DELETING.
 3) In nvme_check_ready(), we always return true when ctrl->state is
    NVME_CTRL_DELETING, so those retrying I/Os were issued to the bottom
    device which was already freed.

To fix this, when ctrl->state is NVME_CTRL_DELETING, issue cmd to bottom
device only when queue state is live.  If not, return host path error to
the block layer
Signed-off-by: Ruozhu Li <liruozhu@huawei.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/core.c

@@ -666,6 +666,7 @@ blk_status_t nvme_fail_nonready_command(struct nvme_ctrl *ctrl,
 		struct request *rq)
 {
 	if (ctrl->state != NVME_CTRL_DELETING_NOIO &&
+	    ctrl->state != NVME_CTRL_DELETING &&
 	    ctrl->state != NVME_CTRL_DEAD &&
 	    !test_bit(NVME_CTRL_FAILFAST_EXPIRED, &ctrl->flags) &&
 	    !blk_noretry_request(rq) && !(rq->cmd_flags & REQ_NVME_MPATH))

drivers/nvme/host/nvme.h

@@ -709,7 +709,7 @@ static inline bool nvme_check_ready(struct nvme_ctrl *ctrl, struct request *rq,
 		return true;
 	if (ctrl->ops->flags & NVME_F_FABRICS &&
 	    ctrl->state == NVME_CTRL_DELETING)
-		return true;
+		return queue_live;
 	return __nvme_check_ready(ctrl, rq, queue_live);
 }
 int nvme_submit_sync_cmd(struct request_queue *q, struct nvme_command *cmd,