On Wed, Jun 17, 2020 at 02:28:11PM +0300, Leon Romanovsky wrote:

On Wed, Jun 17, 2020 at 04:07:32PM +0530, haris.iqbal@cloud.ionos.com wrote:

quoted

From: Md Haris Iqbal <redacted>

Fixes: 2de6c8de192b ("block/rnbd: server: main functionality")
Reported-by: kernel test robot <redacted>
Signed-off-by: Md Haris Iqbal <redacted>

The rnbd_server module's communication manager initialization depends on the
registration of the "network namespace subsystem" of the RDMA CM agent module.
As such, when the kernel is configured to load the rnbd_server and the RDMA
cma module during initialization; and if the rnbd_server module is initialized
before RDMA cma module, a null ptr dereference occurs during the RDMA bind
operation.
This patch delays the initialization of the rnbd_server module to the
late_initcall level, since RDMA cma module uses module_init which puts it into
the device_initcall level.
 drivers/block/rnbd/rnbd-srv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/rnbd/rnbd-srv.c b/drivers/block/rnbd/rnbd-srv.c
index 86e61523907b..213df05e5994 100644
+++ b/drivers/block/rnbd/rnbd-srv.c

@@ -840,5 +840,5 @@ static void __exit rnbd_srv_cleanup_module(void)
 	rnbd_srv_destroy_sysfs_files();
 }

-module_init(rnbd_srv_init_module);
+late_initcall(rnbd_srv_init_module);

I don't think that this is correct change. Somehow nvme-rdma works:
module_init(nvme_rdma_init_module);
-> nvme_rdma_init_module
 -> nvmf_register_transport(&nvme_rdma_transport);
  -> nvme_rdma_create_ctrl
   -> nvme_rdma_setup_ctrl
    -> nvme_rdma_configure_admin_queue
     -> nvme_rdma_alloc_queue
      -> rdma_create_id

If it does work, it is by luck.

Keep in mind all this only matters for kernels without modules.

Maybe cma should be upgraded to subsystem_init ? That is a bit tricky
too as it needs the ib_client stuff working

Jason