Re: [PATCH for-next 02/18] RMDA/rtrs-srv: Occasionally flush ongoing session closing

[Jinpu Wang <jinpu.wang@cloud.ionos.com>]

On Sun, Dec 27, 2020 at 10:01 AM Leon Romanovsky <leon@kernel.org> wrote:
>
> On Wed, Dec 16, 2020 at 05:42:17PM +0100, Jinpu Wang wrote:
> > On Fri, Dec 11, 2020 at 5:29 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> > >
> > > On Fri, Dec 11, 2020 at 05:17:36PM +0100, Jack Wang wrote:
> > > >    En, the lockdep was complaining about the new conn_id, I will
> > > >    post the full log if needed next week.  let’s skip this patch for
> > > >    now, will double check!
> > >
> > > That is even more worrysome as the new conn_id already has a different
> > > lock class.
> > >
> > > Jason
> > This is the dmesg of the LOCKDEP warning, it's on kernel 5.4.77, but
> > the latest 5.10 behaves the same.
> >
> > [  500.071552] ======================================================
> > [  500.071648] WARNING: possible circular locking dependency detected
> > [  500.071869] 5.4.77-storage+ #35 Tainted: G           O
> > [  500.071959] ------------------------------------------------------
> > [  500.072054] kworker/1:1/28 is trying to acquire lock:
> > [  500.072200] ffff99653a624390 (&id_priv->handler_mutex){+.+.}, at:
> > rdma_destroy_id+0x55/0x230 [rdma_cm]
> > [  500.072837]
> >                but task is already holding lock:
> > [  500.072938] ffff9d18800f7e80
> > ((work_completion)(&sess->close_work)){+.+.}, at:
> > process_one_work+0x223/0x600
> > [  500.075642]
> >                which lock already depends on the new lock.
> >
> > [  500.075759]
> >                the existing dependency chain (in reverse order) is:
> > [  500.075880]
> >                -> #3 ((work_completion)(&sess->close_work)){+.+.}:
> > [  500.076062]        process_one_work+0x278/0x600
> > [  500.076154]        worker_thread+0x2d/0x3d0
> > [  500.076225]        kthread+0x111/0x130
> > [  500.076290]        ret_from_fork+0x24/0x30
> > [  500.076370]
> >                -> #2 ((wq_completion)rtrs_server_wq){+.+.}:
> > [  500.076482]        flush_workqueue+0xab/0x4b0
> > [  500.076565]        rtrs_srv_rdma_cm_handler+0x71d/0x1500 [rtrs_server]
> > [  500.076674]        cma_ib_req_handler+0x8c4/0x14f0 [rdma_cm]
> > [  500.076770]        cm_process_work+0x22/0x140 [ib_cm]
> > [  500.076857]        cm_req_handler+0x900/0xde0 [ib_cm]
> > [  500.076944]        cm_work_handler+0x136/0x1af2 [ib_cm]
> > [  500.077025]        process_one_work+0x29f/0x600
> > [  500.077097]        worker_thread+0x2d/0x3d0
> > [  500.077164]        kthread+0x111/0x130
> > [  500.077224]        ret_from_fork+0x24/0x30
> > [  500.077294]
> >                -> #1 (&id_priv->handler_mutex/1){+.+.}:
> > [  500.077409]        __mutex_lock+0x7e/0x950
> > [  500.077488]        cma_ib_req_handler+0x787/0x14f0 [rdma_cm]
> > [  500.077582]        cm_process_work+0x22/0x140 [ib_cm]
> > [  500.077669]        cm_req_handler+0x900/0xde0 [ib_cm]
> > [  500.077755]        cm_work_handler+0x136/0x1af2 [ib_cm]
> > [  500.077835]        process_one_work+0x29f/0x600
> > [  500.077907]        worker_thread+0x2d/0x3d0
> > [  500.077973]        kthread+0x111/0x130
> > [  500.078034]        ret_from_fork+0x24/0x30
> > [  500.078095]
> >                -> #0 (&id_priv->handler_mutex){+.+.}:
> > [  500.078196]        __lock_acquire+0x1166/0x1440
> > [  500.078267]        lock_acquire+0x90/0x170
> > [  500.078335]        __mutex_lock+0x7e/0x950
> > [  500.078410]        rdma_destroy_id+0x55/0x230 [rdma_cm]
> > [  500.078498]        rtrs_srv_close_work+0xf2/0x2d0 [rtrs_server]
> > [  500.078586]        process_one_work+0x29f/0x600
> > [  500.078662]        worker_thread+0x2d/0x3d0
> > [  500.078732]        kthread+0x111/0x130
> > [  500.078793]        ret_from_fork+0x24/0x30
> > [  500.078859]
> >                other info that might help us debug this:
> >
> > [  500.078984] Chain exists of:
> >                  &id_priv->handler_mutex -->
> > (wq_completion)rtrs_server_wq --> (work_completion)(&sess->close_work)
> >
> > [  500.079207]  Possible unsafe locking scenario:
> >
> > [  500.079293]        CPU0                    CPU1
> > [  500.079358]        ----                    ----
> > [  500.079358]   lock((work_completion)(&sess->close_work));
> > [  500.079358]
> > lock((wq_completion)rtrs_server_wq);
> > [  500.079358]
> > lock((work_completion)(&sess->close_work));
> > [  500.079358]   lock(&id_priv->handler_mutex);
> > [  500.079358]
> >                 *** DEADLOCK ***
> >
> > [  500.079358] 2 locks held by kworker/1:1/28:
> > [  500.079358]  #0: ffff99652d281f28
> > ((wq_completion)rtrs_server_wq){+.+.}, at:
> > process_one_work+0x223/0x600
> > [  500.079358]  #1: ffff9d18800f7e80
> > ((work_completion)(&sess->close_work)){+.+.}, at:
> > process_one_work+0x223/0x600
> > [  500.079358]
> >                stack backtrace:
> > [  500.079358] CPU: 1 PID: 28 Comm: kworker/1:1 Tainted: G           O
> >      5.4.77-storage+ #35
> > [  500.079358] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> > BIOS 1.10.2-1ubuntu1 04/01/2014
> > [  500.079358] Workqueue: rtrs_server_wq rtrs_srv_close_work [rtrs_server]
> > [  500.079358] Call Trace:
> > [  500.079358]  dump_stack+0x71/0x9b
> > [  500.079358]  check_noncircular+0x17d/0x1a0
> > [  500.079358]  ? __lock_acquire+0x1166/0x1440
> > [  500.079358]  __lock_acquire+0x1166/0x1440
> > [  500.079358]  lock_acquire+0x90/0x170
> > [  500.079358]  ? rdma_destroy_id+0x55/0x230 [rdma_cm]
> > [  500.079358]  ? rdma_destroy_id+0x55/0x230 [rdma_cm]
> > [  500.079358]  __mutex_lock+0x7e/0x950
> > [  500.079358]  ? rdma_destroy_id+0x55/0x230 [rdma_cm]
> > [  500.079358]  ? find_held_lock+0x2d/0x90
> > [  500.079358]  ? mark_held_locks+0x49/0x70
> > [  500.079358]  ? rdma_destroy_id+0x55/0x230 [rdma_cm]
> > [  500.079358]  rdma_destroy_id+0x55/0x230 [rdma_cm]
> > [  500.079358]  rtrs_srv_close_work+0xf2/0x2d0 [rtrs_server]
> > [  500.079358]  process_one_work+0x29f/0x600
> > [  500.079358]  worker_thread+0x2d/0x3d0
> > [  500.079358]  ? process_one_work+0x600/0x600
> > [  500.079358]  kthread+0x111/0x130
> > [  500.079358]  ? kthread_park+0x90/0x90
> > [  500.079358]  ret_from_fork+0x24/0x30
> >
> > According to my understanding
> > in cma_ib_req_handler, the conn_id is newly created in
> > https://elixir.bootlin.com/linux/latest/source/drivers/infiniband/core/cma.c#L2222.
> > And the rdma_cm_id associated with conn_id is passed to
> > rtrs_srv_rdma_cm_handler->rtrs_rdma_connect.
> >
> > In rtrs_rdma_connect, we do flush_workqueue will only flush close_work
> > for any other cm_id, but
> > not the newly created one conn_id, it has not associated with anything yet.
>
> How did you come to this conclusion that rtrs handler was called before
> cma_cm_event_handler()? I'm not so sure about that and it will explain
> the lockdep.
>
> Thanks
Hi Leon,
I never said that, the call chain here is:
cma_ib_req_handler->cma_cm_event_handler->rtrs_srv_rdma_cm_handler->rtrs_rdma_connect.
Repeat myself in last email:
in cma_ib_req_handler, the conn_id is newly created in
 https://elixir.bootlin.com/linux/latest/source/drivers/infiniband/core/cma.c#L2222.
And the rdma_cm_id associated with conn_id is passed to
rtrs_rdma_connect.

In rtrs_rdma_connect, we do flush_workqueue will only flush close_work
for any other cm_id, but
not the newly created one conn_id, the rdma_cm_id passed in
rtrs_rdma_connect has not associated with anything yet.

Hope this is now clear.

Happy New Year!