Re: [PATCH] Delay the initialization of rnbd_server module to late_initcall level

[Jason Gunthorpe <jgg@ziepe.ca>]

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:
> > From: Md Haris Iqbal <haris.iqbal@cloud.ionos.com>
> >
> > Fixes: 2de6c8de192b ("block/rnbd: server: main functionality")
> > Reported-by: kernel test robot <rong.a.chen@intel.com>
> > Signed-off-by: Md Haris Iqbal <haris.iqbal@cloud.ionos.com>
> >
> > 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