nvme: do not let the user delete a ctrl before a complete initialization

If a userspace application performes a "delete_controller" command
early during the ctrl initialization, the delete operation
may race against the init code and the kernel will crash.

nvme nvme5: Connect command failed: host path error
nvme nvme5: failed to connect queue: 0 ret=880
PF: supervisor write access in kernel mode
PF: error_code(0x0002) - not-present page
 blk_mq_quiesce_queue+0x18/0x90
 nvme_tcp_delete_ctrl+0x24/0x40 [nvme_tcp]
 nvme_do_delete_ctrl+0x7f/0x8b [nvme_core]
 nvme_sysfs_delete.cold+0x8/0xd [nvme_core]
 kernfs_fop_write_iter+0x124/0x1b0
 new_sync_write+0xff/0x190
 vfs_write+0x1ef/0x280

Fix the crash by checking the NVME_CTRL_STARTED_ONCE bit;
if it's not set it means that the nvme controller is still
in the process of getting initialized and the kernel
will return an -EBUSY error to userspace.
Set the NVME_CTRL_STARTED_ONCE later in the nvme_start_ctrl()
function, after the controller start operation is completed.
Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>

drivers/nvme/host/core.c

@@ -3574,6 +3574,9 @@ static ssize_t nvme_sysfs_delete(struct device *dev,
 {
 	struct nvme_ctrl *ctrl = dev_get_drvdata(dev);
 
+	if (!test_bit(NVME_CTRL_STARTED_ONCE, &ctrl->flags))
+		return -EBUSY;
+
 	if (device_remove_file_self(dev, attr))
 		nvme_delete_ctrl_sync(ctrl);
 	return count;
@@ -5034,7 +5037,7 @@ void nvme_start_ctrl(struct nvme_ctrl *ctrl)
 	 * that were missed. We identify persistent discovery controllers by
 	 * checking that they started once before, hence are reconnecting back.
 	 */
-	if (test_and_set_bit(NVME_CTRL_STARTED_ONCE, &ctrl->flags) &&
+	if (test_bit(NVME_CTRL_STARTED_ONCE, &ctrl->flags) &&
 	    nvme_discovery_ctrl(ctrl))
 		nvme_change_uevent(ctrl, "NVME_EVENT=rediscover");
 
@@ -5045,6 +5048,7 @@ void nvme_start_ctrl(struct nvme_ctrl *ctrl)
 	}
 
 	nvme_change_uevent(ctrl, "NVME_EVENT=connected");
+	set_bit(NVME_CTRL_STARTED_ONCE, &ctrl->flags);
 }
 EXPORT_SYMBOL_GPL(nvme_start_ctrl);