On Mon, Jan 4, 2021 at 9:25 AM Leon Romanovsky <leon@xxxxxxxxxx> wrote:
>
> On Mon, Jan 04, 2021 at 09:06:13AM +0100, Jinpu Wang wrote:
> > On Sun, Dec 27, 2020 at 10:01 AM Leon Romanovsky <leon@xxxxxxxxxx> 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@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
> > 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.
>
> This is exactly why I'm not so sure, after rdma_cm_id returns from
> RDMA/core, it will be in that flush_workqueue queue.
In rtrs_rdma_connect, we do flush_workqueue(rtrs_wq) in the
beginning before we associate rdma_cm_id (conn_id) to rtrs_srv_con in
by rtrs_srv_rdma_cm_handler -> rtrs_rdma_connect -> create_con ->
con->c.cm_id = cm_id. And in rtrs_srv_close_work we do
rdma_destroy_id(con->c.cm_id);
so the rdma_cm_id is not in the flush_workqueue queue yet.
Thanks!
>
> >
> > Hope this is now clear.
> >
> > Happy New Year!
>
> Happy New Year too :)
