nvme: release namespace SRCU protection before performing controller ioctls

Holding the SRCU critical section protecting the namespace list can
cause deadlocks when using the per-namespace admin passthrough ioctl to
delete as namespace. Release it earlier when performing per-controller
ioctls to avoid that.

Reported-by: Kenneth Heitke <[e-mail]>
Reviewed-by: Chaitanya Kulkarni <[e-mail]>
Reviewed-by: Keith Busch <[e-mail]>
Signed-off-by: Christoph Hellwig <[e-mail]>

drivers/nvme/host/core.c

···
 	if (unlikely(!ns))
 		return -EWOULDBLOCK;
 
+	/*
+	 * Handle ioctls that apply to the controller instead of the namespace
+	 * seperately and drop the ns SRCU reference early.  This avoids a
+	 * deadlock when deleting namespaces using the passthrough interface.
+	 */
+	if (cmd == NVME_IOCTL_ADMIN_CMD || is_sed_ioctl(cmd)) {
+		struct nvme_ctrl *ctrl = ns->ctrl;
+
+		nvme_get_ctrl(ns->ctrl);
+		nvme_put_ns_from_disk(head, srcu_idx);
+
+		if (cmd == NVME_IOCTL_ADMIN_CMD)
+			ret = nvme_user_cmd(ctrl, NULL, argp);
+		else
+			ret = sed_ioctl(ctrl->opal_dev, cmd, argp);
+
+		nvme_put_ctrl(ctrl);
+		return ret;
+	}
+
 	switch (cmd) {
 	case NVME_IOCTL_ID:
 		force_successful_syscall_return();
 		ret = ns->head->ns_id;
-		break;
-	case NVME_IOCTL_ADMIN_CMD:
-		ret = nvme_user_cmd(ns->ctrl, NULL, argp);
 		break;
 	case NVME_IOCTL_IO_CMD:
 		ret = nvme_user_cmd(ns->ctrl, ns, argp);
···
 	default:
 		if (ns->ndev)
 			ret = nvme_nvm_ioctl(ns, cmd, arg);
-		else if (is_sed_ioctl(cmd))
-			ret = sed_ioctl(ns->ctrl->opal_dev, cmd, argp);
 		else
 			ret = -ENOTTY;
 	}