Re: [PATCH v2] RDMA/rtrs-srv: Incorporate ib_register_client into rtrs server init

[Leon Romanovsky <leon@kernel.org>]

On Wed, Aug 05, 2020 at 07:23:58PM +0530, Haris Iqbal wrote:
> On Wed, Aug 5, 2020 at 6:42 PM Leon Romanovsky <leon@kernel.org> wrote:
> >
> > On Wed, Aug 05, 2020 at 04:39:16PM +0530, Haris Iqbal wrote:
> > > On Wed, Aug 5, 2020 at 2:34 PM Leon Romanovsky <leon@kernel.org> wrote:
> > > >
> > > > On Wed, Aug 05, 2020 at 01:20:09PM +0530, Haris Iqbal wrote:
> > > > > On Wed, Aug 5, 2020 at 11:27 AM Leon Romanovsky <leon@kernel.org> wrote:
> > > > > >
> > > > > > On Tue, Aug 04, 2020 at 07:07:58PM +0530, Md Haris Iqbal wrote:
> > > > > > > The rnbd_server module's communication manager (cm) 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.
> > > > > > >
> > > > > > > Call trace below,
> > > > > > >
> > > > > > > [    1.904782] Call Trace:
> > > > > > > [    1.904782]  ? xas_load+0xd/0x80
> > > > > > > [    1.904782]  xa_load+0x47/0x80
> > > > > > > [    1.904782]  cma_ps_find+0x44/0x70
> > > > > > > [    1.904782]  rdma_bind_addr+0x782/0x8b0
> > > > > > > [    1.904782]  ? get_random_bytes+0x35/0x40
> > > > > > > [    1.904782]  rtrs_srv_cm_init+0x50/0x80
> > > > > > > [    1.904782]  rtrs_srv_open+0x102/0x180
> > > > > > > [    1.904782]  ? rnbd_client_init+0x6e/0x6e
> > > > > > > [    1.904782]  rnbd_srv_init_module+0x34/0x84
> > > > > > > [    1.904782]  ? rnbd_client_init+0x6e/0x6e
> > > > > > > [    1.904782]  do_one_initcall+0x4a/0x200
> > > > > > > [    1.904782]  kernel_init_freeable+0x1f1/0x26e
> > > > > > > [    1.904782]  ? rest_init+0xb0/0xb0
> > > > > > > [    1.904782]  kernel_init+0xe/0x100
> > > > > > > [    1.904782]  ret_from_fork+0x22/0x30
> > > > > > > [    1.904782] Modules linked in:
> > > > > > > [    1.904782] CR2: 0000000000000015
> > > > > > > [    1.904782] ---[ end trace c42df88d6c7b0a48 ]---
> > > > > > >
> > > > > > > All this happens cause the cm init is in the call chain of the module init,
> > > > > > > which is not a preferred practice.
> > > > > > >
> > > > > > > So remove the call to rdma_create_id() from the module init call chain.
> > > > > > > Instead register rtrs-srv as an ib client, which makes sure that the
> > > > > > > rdma_create_id() is called only when an ib device is added.
> > > > > > >
> > > > > > > Fixes: 9cb837480424 ("RDMA/rtrs: server: main functionality")
> > > > > > > Reported-by: kernel test robot <rong.a.chen@intel.com>
> > > > > > > Signed-off-by: Md Haris Iqbal <haris.iqbal@cloud.ionos.com>
> > > > > > > ---
> > > > > > >  drivers/infiniband/ulp/rtrs/rtrs-srv.c | 77 +++++++++++++++++++++++++-
> > > > > > >  drivers/infiniband/ulp/rtrs/rtrs-srv.h |  7 +++
> > > > > > >  2 files changed, 81 insertions(+), 3 deletions(-)
> > > > > >
> > > > > > Please don't send vX patches as reply-to in "git send-email" command.
> > > > > >
> > > > > > >
> > > > > > > diff --git a/drivers/infiniband/ulp/rtrs/rtrs-srv.c b/drivers/infiniband/ulp/rtrs/rtrs-srv.c
> > > > > > > index 0d9241f5d9e6..916f99464d09 100644
> > > > > > > --- a/drivers/infiniband/ulp/rtrs/rtrs-srv.c
> > > > > > > +++ b/drivers/infiniband/ulp/rtrs/rtrs-srv.c
> > > > > > > @@ -16,6 +16,7 @@
> > > > > > >  #include "rtrs-srv.h"
> > > > > > >  #include "rtrs-log.h"
> > > > > > >  #include <rdma/ib_cm.h>
> > > > > > > +#include <rdma/ib_verbs.h>
> > > > > > >
> > > > > > >  MODULE_DESCRIPTION("RDMA Transport Server");
> > > > > > >  MODULE_LICENSE("GPL");
> > > > > > > @@ -31,6 +32,7 @@ MODULE_LICENSE("GPL");
> > > > > > >  static struct rtrs_rdma_dev_pd dev_pd;
> > > > > > >  static mempool_t *chunk_pool;
> > > > > > >  struct class *rtrs_dev_class;
> > > > > > > +static struct rtrs_srv_ib_ctx ib_ctx;
> > > > > > >
> > > > > > >  static int __read_mostly max_chunk_size = DEFAULT_MAX_CHUNK_SIZE;
> > > > > > >  static int __read_mostly sess_queue_depth = DEFAULT_SESS_QUEUE_DEPTH;
> > > > > > > @@ -2033,6 +2035,62 @@ static void free_srv_ctx(struct rtrs_srv_ctx *ctx)
> > > > > > >       kfree(ctx);
> > > > > > >  }
> > > > > > >
> > > > > > > +static int rtrs_srv_add_one(struct ib_device *device)
> > > > > > > +{
> > > > > > > +     struct rtrs_srv_ctx *ctx;
> > > > > > > +     int ret;
> > > > > > > +
> > > > > > > +     /*
> > > > > > > +      * Keep a track on the number of ib devices added
> > > > > > > +      */
> > > > > > > +     ib_ctx.ib_dev_count++;
> > > > > > > +
> > > > > > > +     if (!ib_ctx.rdma_init) {
> > > > > > > +             /*
> > > > > > > +              * Since our CM IDs are NOT bound to any ib device we will create them
> > > > > > > +              * only once
> > > > > > > +              */
> > > > > > > +             ctx = ib_ctx.srv_ctx;
> > > > > > > +             ret = rtrs_srv_rdma_init(ctx, ib_ctx.port);
> > > > > > > +             if (ret) {
> > > > > > > +                     /*
> > > > > > > +                      * We errored out here.
> > > > > > > +                      * According to the ib code, if we encounter an error here then the
> > > > > > > +                      * error code is ignored, and no more calls to our ops are made.
> > > > > > > +                      */
> > > > > > > +                     pr_err("Failed to initialize RDMA connection");
> > > > > > > +                     return ret;
> > > > > > > +             }
> > > > > > > +             ib_ctx.rdma_init = true;
> > > > > >
> > > > > > This rdma_init == false is equal to ib_ctx.ib_dev_count == 0 and the
> > > > > > logic can be simplified.
> > > > >
> > > > > Yes, this was the first logic in my head. But I have few thoughts,
> > > > > The below suggestions uses "ib_ctx.ib_dev_count" as a marker for
> > > > > successful execution of rtrs_srv_rdma_init() and not really an IB
> > > > > device count. Meaning if we have multiple calls to add, due to
> > > > > multiple devices, our count would stay 1. And while removal we might
> > > > > end up calling rdma_destroy_id() on our first remove call even though
> > > > > another device is still remaining.
> > > > >
> > > > > If we increment "ib_ctx.ib_dev_count" every time add is called, even
> > > > > before we call rtrs_srv_rdma_init() and irrespective of whether
> > > > > rtrs_srv_rdma_init() succeeds or not, then we are keeping a count of
> > > > > IB devices added. However, when remove is called, we now know the
> > > > > number of devices added, but not whether rtrs_srv_rdma_init() was
> > > > > successful or not. We may end up calling rdma_destroy_id() on NULL
> > > > > cm_ids
> > > > >
> > > > > Does this make sense or am I missing something?
> > > > >
> > > > >
> > > > > >
> > > > > > if (ib_ctx.ib_dev_count)
> > > > > >         return 0;
> > >
> > > My understanding is, with the above 2 lines, after one add in which
> > > rtrs_srv_rdma_init() succeeds, we won't even go below this, and hence
> > > subsequent increments will not happen.
> >
> > Is it better?
> >
> > if (ib_ctx.ib_dev_count)
> >   goto out;
> >
> > ....
> >
> > out:
> >   ib_ctx.ib_dev_count++;
> >   return 0;
> >
> > You don't need to take the code proposed in the ML as is.
>
> Yes, hence I posted a theoretical scenario which discussed 2 possible scenarios.
>
> case 1, single variable tracking only number of devices added.
> when remove is called, we now know the
> number of devices added, but not whether rtrs_srv_rdma_init() was
> successful or not. We may end up calling rdma_destroy_id() on NULL
> cm_ids

If rtrs_srv_rdma_init() fails to initialize on first attempt, why do you
want to continue to load rtrs?

>
> case 2, single variable tracking success of rtrs_srv_rdma_init()
> If we have multiple IB devices added, while removal we won't know when
> to call rdma_destroy_id(),

Your code doesn't know it either, it calls to destroy on last ib_dev.

>
> >
> > >
> > > > > >
> > > > > > ctx = ib_ctx.srv_ctx;
> > > > > > ret = rtrs_srv_rdma_init(ctx, ib_ctx.port);
> > > > > > if (ret)
> > > > > >         return ret;
> > >
> > > Also here, when rtrs_srv_rdma_init() fails, we return without
> > > incrementing. IMHO, in this logic, we are not using
> > > "ib_ctx.ib_dev_count" to track the number of devices, but to mark
> > > successful execution of rtrs_srv_rdma_init()
> >
> > Of course, you should increment in success only.
>
> I am confused again. What exactly are you suggesting we track with
> "ib_ctx.ib_dev_count"?
> According to my understanding, we can't possibly track both "number of
> devices added" and "success of rtrs_srv_rdma_init()".

Why don't you ask your colleagues? They will guide you.

Thanks