On Fri, 2022-09-16 at 14:28 -0400, Olga Kornievskaia wrote:
> On Thu, Sep 15, 2022 at 11:56 AM Olga Kornievskaia <aglo@xxxxxxxxx>
> wrote:
> >
> > On Tue, Sep 6, 2022 at 12:25 PM Chuck Lever
> > <chuck.lever@xxxxxxxxxx> wrote:
> > >
> > > While setting up a new lab, I accidentally misconfigured the
> > > Ethernet port for a system that tried an NFS mount using RoCE.
> > > This made the NFS server unreachable. The following WARNING
> > > popped on the NFS client while waiting for the mount attempt to
> > > time out:
> >
> > I also hit this today (on the 5.18 kernel) while running xfstest
> > generic/460 using soft iWarp. In my case the port was properly
> > configured. The test was going. I'm not sure exactly what happened.
> > I
> > know I also crashed the server that I was running against. But the
> > point I would like to make is that this condition is possible to
> > get
> > to on a properly configured system.
>
> But I think with this patch. I'm hitting this instead (of course
> could
> be something else):
>
> [ 3222.712335] BUG: using smp_processor_id() in preemptible
> [00000000]
> code: 192.168.1.124-m/3814
> [ 3222.714428] caller is xprt_rdma_connect+0x6a/0x120 [rpcrdma]
> [ 3222.716047] CPU: 0 PID: 3814 Comm: 192.168.1.124-m Not tainted
> 6.0.0-rc5+ #123
> [ 3222.717706] Hardware name: VMware, Inc. VMware Virtual
> Platform/440BX Desktop Reference Platform, BIOS 6.00 11/12/2020
> [ 3222.720310] Call Trace:
> [ 3222.721032] <TASK>
> [ 3222.721587] dump_stack_lvl+0x33/0x46
> [ 3222.722501] check_preemption_disabled+0xc3/0xf0
> [ 3222.723754] xprt_rdma_connect+0x6a/0x120 [rpcrdma]
> [ 3222.725594] xprt_connect+0x300/0x370 [sunrpc]
> [ 3222.727369] ? call_reserveresult+0xa0/0xa0 [sunrpc]
> [ 3222.729272] __rpc_execute+0x162/0x870 [sunrpc]
> [ 3222.731101] ? rpc_exit+0x40/0x40 [sunrpc]
> [ 3222.732841] ? __wake_up+0x10/0x10
> [ 3222.733657] rpc_execute+0x148/0x1b0 [sunrpc]
> [ 3222.735326] rpc_run_task+0x270/0x2d0 [sunrpc]
> [ 3222.737182] nfs4_proc_bind_one_conn_to_session+0x1cc/0x3a0
> [nfsv4]
> [ 3222.740472] ? _nfs4_do_set_security_label+0x2d0/0x2d0 [nfsv4]
> [ 3222.745034] ? xprt_get+0xa0/0x120 [sunrpc]
> [ 3222.747150] ? nfs4_proc_bind_one_conn_to_session+0x3a0/0x3a0
> [nfsv4]
> [ 3222.749299] ? __rcu_read_unlock+0x4e/0x250
> [ 3222.750429] ? nfs4_proc_bind_one_conn_to_session+0x3a0/0x3a0
> [nfsv4]
> [ 3222.752586] rpc_clnt_iterate_for_each_xprt+0xc6/0x140 [sunrpc]
> [ 3222.754900] ? rpc_clnt_xprt_switch_add_xprt+0xa0/0xa0 [sunrpc]
> [ 3222.757041] ? preempt_count_sub+0x14/0xc0
> [ 3222.758097] nfs4_proc_bind_conn_to_session+0x87/0xb0 [nfsv4]
> [ 3222.760341] ? nfs4_proc_secinfo+0x250/0x250 [nfsv4]
> [ 3222.762257] nfs4_state_manager+0x34e/0xf60 [nfsv4]
> [ 3222.764095] nfs4_run_state_manager+0x1a6/0x2e0 [nfsv4]
> [ 3222.766778] ? nfs4_state_manager+0xf60/0xf60 [nfsv4]
> [ 3222.768811] ? _raw_spin_lock_irqsave+0x8d/0xf0
> [ 3222.770029] ? _raw_spin_unlock_irqrestore+0x40/0x40
> [ 3222.771740] ? __list_del_entry_valid+0x77/0xa0
> [ 3222.773400] ? nfs4_state_manager+0xf60/0xf60 [nfsv4]
> [ 3222.775653] kthread+0x160/0x190
> [ 3222.776729] ? kthread_complete_and_exit+0x20/0x20
> [ 3222.777865] ret_from_fork+0x1f/0x30
> [ 3222.778972] </TASK>
>
>
> >
> > > kernel: workqueue: WQ_MEM_RECLAIM
> > > xprtiod:xprt_rdma_connect_worker [rpcrdma] is flushing
> > > !WQ_MEM_RECLAI>
> > > kernel: WARNING: CPU: 0 PID: 100 at kernel/workqueue.c:2628
> > > check_flush_dependency+0xbf/0xca
> > > kernel: Modules linked in: rpcsec_gss_krb5 nfsv4 dns_resolver nfs
> > > 8021q garp stp mrp llc rfkill rpcrdma>
> > > kernel: CPU: 0 PID: 100 Comm: kworker/u8:8 Not tainted 6.0.0-rc1-
> > > 00002-g6229f8c054e5 #13
> > > kernel: Hardware name: Supermicro X10SRA-F/X10SRA-F, BIOS 2.0b
> > > 06/12/2017
> > > kernel: Workqueue: xprtiod xprt_rdma_connect_worker [rpcrdma]
> > > kernel: RIP: 0010:check_flush_dependency+0xbf/0xca
> > > kernel: Code: 75 2a 48 8b 55 18 48 8d 8b b0 00 00 00 4d 89 e0 48
> > > 81 c6 b0 00 00 00 48 c7 c7 65 33 2e be>
> > > kernel: RSP: 0018:ffffb562806cfcf8 EFLAGS: 00010092
> > > kernel: RAX: 0000000000000082 RBX: ffff97894f8c3c00 RCX:
> > > 0000000000000027
> > > kernel: RDX: 0000000000000002 RSI: ffffffffbe3447d1 RDI:
> > > 00000000ffffffff
> > > kernel: RBP: ffff978941315840 R08: 0000000000000000 R09:
> > > 0000000000000000
> > > kernel: R10: 00000000000008b0 R11: 0000000000000001 R12:
> > > ffffffffc0ce3731
> > > kernel: R13: ffff978950c00500 R14: ffff97894341f0c0 R15:
> > > ffff978951112eb0
> > > kernel: FS: 0000000000000000(0000) GS:ffff97987fc00000(0000)
> > > knlGS:0000000000000000
> > > kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > kernel: CR2: 00007f807535eae8 CR3: 000000010b8e4002 CR4:
> > > 00000000003706f0
> > > kernel: DR0: 0000000000000000 DR1: 0000000000000000 DR2:
> > > 0000000000000000
> > > kernel: DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
> > > 0000000000000400
> > > kernel: Call Trace:
> > > kernel: <TASK>
> > > kernel: __flush_work.isra.0+0xaf/0x188
> > > kernel: ? _raw_spin_lock_irqsave+0x2c/0x37
> > > kernel: ? lock_timer_base+0x38/0x5f
> > > kernel: __cancel_work_timer+0xea/0x13d
> > > kernel: ? preempt_latency_start+0x2b/0x46
> > > kernel: rdma_addr_cancel+0x70/0x81 [ib_core]
> > > kernel: _destroy_id+0x1a/0x246 [rdma_cm]
> > > kernel: rpcrdma_xprt_connect+0x115/0x5ae [rpcrdma]
> > > kernel: ? _raw_spin_unlock+0x14/0x29
> > > kernel: ? raw_spin_rq_unlock_irq+0x5/0x10
> > > kernel: ? finish_task_switch.isra.0+0x171/0x249
> > > kernel: xprt_rdma_connect_worker+0x3b/0xc7 [rpcrdma]
> > > kernel: process_one_work+0x1d8/0x2d4
> > > kernel: worker_thread+0x18b/0x24f
> > > kernel: ? rescuer_thread+0x280/0x280
> > > kernel: kthread+0xf4/0xfc
> > > kernel: ? kthread_complete_and_exit+0x1b/0x1b
> > > kernel: ret_from_fork+0x22/0x30
> > > kernel: </TASK>
> > >
> > > SUNRPC's xprtiod workqueue is WQ_MEM_RECLAIM, so any workqueue
> > > that
> > > one of its work items tries to cancel has to be WQ_MEM_RECLAIM to
> > > prevent a priority inversion. The internal workqueues in the
> > > RDMA/core are currently non-MEM_RECLAIM.
> > >
> > > Jason Gunthorpe says this about the current state of RDMA/core:
> > > > If you attempt to do a reconnection/etc from within a RECLAIM
> > > > context it will deadlock on one of the many allocations that
> > > > are
> > > > made to support opening the connection.
> > > >
> > > > The general idea of reclaim is that the entire task context
> > > > working under the reclaim is marked with an override of the gfp
> > > > flags to make all allocations under that call chain reclaim
> > > > safe.
> > > >
> > > > But rdmacm does allocations outside this, eg in the WQs
> > > > processing
> > > > the CM packets. So this doesn't work and we will deadlock.
> > > >
> > > > Fixing it is a big deal and needs more than poking
> > > > WQ_MEM_RECLAIM
> > > > here and there.
> > >
> > > So we will change the ULP in this case to avoid the use of
> > > WQ_MEM_RECLAIM where possible. Deadlocks that were possible
> > > before
> > > are not fixed, but at least we no longer have a false sense of
> > > confidence that the stack won't allocate memory during memory
> > > reclaim.
> > >
> > > While we're adjusting these queue_* call sites, ensure the work
> > > requests always run on the local CPU so the worker allocates RDMA
> > > resources that are local to the CPU that queued the work request.
> > >
> > > Suggested-by: Leon Romanovsky <leon@xxxxxxxxxx>
> > > Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> > > ---
> > > net/sunrpc/xprtrdma/transport.c | 4 ++--
> > > net/sunrpc/xprtrdma/verbs.c | 11 ++++-------
> > > 2 files changed, 6 insertions(+), 9 deletions(-)
> > >
> > > Hi Anna-
> > >
> > > I've had this applied to my test client for a while. I think it's
> > > ready to apply.
> > >
> > >
> > > diff --git a/net/sunrpc/xprtrdma/transport.c
> > > b/net/sunrpc/xprtrdma/transport.c
> > > index bcb37b51adf6..9581641bb8cb 100644
> > > --- a/net/sunrpc/xprtrdma/transport.c
> > > +++ b/net/sunrpc/xprtrdma/transport.c
> > > @@ -494,8 +494,8 @@ xprt_rdma_connect(struct rpc_xprt *xprt,
> > > struct rpc_task *task)
> > > xprt_reconnect_backoff(xprt,
> > > RPCRDMA_INIT_REEST_TO);
> > > }
> > > trace_xprtrdma_op_connect(r_xprt, delay);
> > > - queue_delayed_work(xprtiod_workqueue, &r_xprt-
> > > >rx_connect_worker,
> > > - delay);
> > > + queue_delayed_work_on(smp_processor_id(), system_long_wq,
> > > + &r_xprt->rx_connect_worker, delay);
> > > }
> > >
> > > /**
> > > diff --git a/net/sunrpc/xprtrdma/verbs.c
> > > b/net/sunrpc/xprtrdma/verbs.c
> > > index 2fbe9aaeec34..691afc96bcbc 100644
> > > --- a/net/sunrpc/xprtrdma/verbs.c
> > > +++ b/net/sunrpc/xprtrdma/verbs.c
> > > @@ -791,13 +791,10 @@ void rpcrdma_mrs_refresh(struct
> > > rpcrdma_xprt *r_xprt)
> > > /* If there is no underlying connection, it's no use
> > > * to wake the refresh worker.
> > > */
> > > - if (ep->re_connect_status == 1) {
> > > - /* The work is scheduled on a WQ_MEM_RECLAIM
> > > - * workqueue in order to prevent MR allocation
> > > - * from recursing into NFS during direct reclaim.
> > > - */
> > > - queue_work(xprtiod_workqueue, &buf-
> > > >rb_refresh_worker);
> > > - }
> > > + if (ep->re_connect_status != 1)
> > > + return;
> > > + queue_work_on(smp_processor_id(), system_highpri_wq,
> > > + &buf->rb_refresh_worker);
> > > }
> > >
> > > /**
> > >
> > >
Right. smp_processor_id() is only allowed to be called when preemption
has been disabled. See Documentation/kernel-hacking/hacking.rst and
Documentation/locking/preempt-locking.rst.
Why not just use queue_work(), Chuck? That achieves the exact same
thing without requiring any extra locking.
--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@xxxxxxxxxxxxxxx
