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

[Jason Gunthorpe <jgg@ziepe.ca>]

On Tue, Jun 23, 2020 at 07:15:03PM +0530, Haris Iqbal wrote:
> On Tue, Jun 23, 2020 at 5:47 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> >
> > On Tue, Jun 23, 2020 at 03:20:27PM +0530, Haris Iqbal wrote:
> > > Hi Jason and Leon,
> > >
> > > Did you get a chance to look into my previous email?
> >
> > Was there a question?
> 
> Multiple actually :)
> 
> >
> > Jason
> 
> In response to your emails,
> 
> > Somehow nvme-rdma works:
> 
> I think that's because the callchain during the nvme_rdma_init_module
> initialization stops at "nvmf_register_transport()". Here only the
> "struct nvmf_transport_ops nvme_rdma_transport" is registered, which
> contains the function "nvme_rdma_create_ctrl()". I tested this in my
> local setup and during kernel boot, that's the extent of the
> callchain.
> The ".create_ctrl"; which now points to "nvme_rdma_create_ctrl()" is
> called later from "nvmf_dev_write()". I am not sure when this is
> called, probably when the "discover" happens from the client side or
> during the server config.
> 
> It seems that the "rdma_bind_addr()" is called by the nvme rdma
> module; but during the following events
> 1) When a discover happens from the client side. Call trace for that looks like,
> [ 1098.409398] nvmf_dev_write
> [ 1098.409403] nvmf_create_ctrl
> [ 1098.414568] nvme_rdma_create_ctrl
> [ 1098.415009] nvme_rdma_setup_ctrl
> [ 1098.415010] nvme_rdma_configure_admin_queue
> [ 1098.415010] nvme_rdma_alloc_queue
> [ 1098.415032] rdma_resolve_addr
> [ 1098.415032] cma_bind_addr
> [ 1098.415033] rdma_bind_addr
> 
> 2) When a connect happens from the client side. Call trace is the same
> as above, plus "nvme_rdma_alloc_queue()" is called n number of times;
> n being the number of IO queues being created.
> 
> On the server side, when an nvmf port is enabled, that also triggers a
> call to "rdma_bind_addr()", but that is not from the nvme rdma module.
> may be nvme target rdma? (not sure).
> 
> Does this make sense or am I missing something here?

It make sense, delaying creating and CM ID's until user space starts
will solve this init time problme

> 
> > If the rdma_create_id() is not on a callchain from module_init then you don't have a problem.
> 
> I am a little confused. I thought the problem occurs from a call to
> either "rdma_resolve_addr()" which calls "rdma_bind_addr()",
> or a direct call to "rdma_bind_addr()" as in rtrs case.
> In both the cases, a call to "rdma_create_id()" is needed before this.

Right rdma_create_id() must precede anything that has problems, and it
should not be done from module_init.

Jason