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@xxxxxxxx> 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
>
> The same applies to nvme-rdma. so it's a false alarm by lockdep.
>
> Regards!
