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Message-ID: <31920.1414126114@famine>
Date: Thu, 23 Oct 2014 21:48:34 -0700
From: Jay Vosburgh <jay.vosburgh@...onical.com>
To: paulmck@...ux.vnet.ibm.com
cc: Yanko Kaneti <yaneti@...lera.com>,
Josh Boyer <jwboyer@...oraproject.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Cong Wang <cwang@...pensource.com>,
Kevin Fenzi <kevin@...ye.com>, netdev <netdev@...r.kernel.org>,
"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: Re: localed stuck in recent 3.18 git in copy_net_ns?
Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:
>On Fri, Oct 24, 2014 at 12:45:40AM +0300, Yanko Kaneti wrote:
>>
>> On Thu, 2014-10-23 at 13:05 -0700, Paul E. McKenney wrote:
>> > On Thu, Oct 23, 2014 at 10:51:59PM +0300, Yanko Kaneti wrote:
>> > > On Thu-10/23/14-2014 08:33, Paul E. McKenney wrote:
>> > > > On Thu, Oct 23, 2014 at 05:27:50AM -0700, Paul E. McKenney wrote:
>> > > > > On Thu, Oct 23, 2014 at 09:09:26AM +0300, Yanko Kaneti wrote:
>> > > > > > On Wed, 2014-10-22 at 16:24 -0700, Paul E. McKenney wrote:
>> > > > > > > On Thu, Oct 23, 2014 at 01:40:32AM +0300, Yanko Kaneti
>> > > > > > > wrote:
>> > > > > > > > On Wed-10/22/14-2014 15:33, Josh Boyer wrote:
>> > > > > > > > > On Wed, Oct 22, 2014 at 2:55 PM, Paul E. McKenney
>> > > > > > > > > <paulmck@...ux.vnet.ibm.com> wrote:
>> > > > > > >
>> > > > > > > [ . . . ]
>> > > > > > >
>> > > > > > > > > > Don't get me wrong -- the fact that this kthread
>> > > > > > > > > > appears to
>> > > > > > > > > > have
>> > > > > > > > > > blocked within rcu_barrier() for 120 seconds means
>> > > > > > > > > > that
>> > > > > > > > > > something is
>> > > > > > > > > > most definitely wrong here. I am surprised that
>> > > > > > > > > > there are no
>> > > > > > > > > > RCU CPU
>> > > > > > > > > > stall warnings, but perhaps the blockage is in the
>> > > > > > > > > > callback
>> > > > > > > > > > execution
>> > > > > > > > > > rather than grace-period completion. Or something is
>> > > > > > > > > > preventing this
>> > > > > > > > > > kthread from starting up after the wake-up callback
>> > > > > > > > > > executes.
>> > > > > > > > > > Or...
>> > > > > > > > > >
>> > > > > > > > > > Is this thing reproducible?
>> > > > > > > > >
>> > > > > > > > > I've added Yanko on CC, who reported the backtrace
>> > > > > > > > > above and can
>> > > > > > > > > recreate it reliably. Apparently reverting the RCU
>> > > > > > > > > merge commit
>> > > > > > > > > (d6dd50e) and rebuilding the latest after that does
>> > > > > > > > > not show the
>> > > > > > > > > issue. I'll let Yanko explain more and answer any
>> > > > > > > > > questions you
>> > > > > > > > > have.
>> > > > > > > >
>> > > > > > > > - It is reproducible
>> > > > > > > > - I've done another build here to double check and its
>> > > > > > > > definitely
>> > > > > > > > the rcu merge
>> > > > > > > > that's causing it.
>> > > > > > > >
>> > > > > > > > Don't think I'll be able to dig deeper, but I can do
>> > > > > > > > testing if
>> > > > > > > > needed.
>> > > > > > >
>> > > > > > > Please! Does the following patch help?
>> > > > > >
>> > > > > > Nope, doesn't seem to make a difference to the modprobe
>> > > > > > ppp_generic
>> > > > > > test
>> > > > >
>> > > > > Well, I was hoping. I will take a closer look at the RCU
>> > > > > merge commit
>> > > > > and see what suggests itself. I am likely to ask you to
>> > > > > revert specific
>> > > > > commits, if that works for you.
>> > > >
>> > > > Well, rather than reverting commits, could you please try
>> > > > testing the
>> > > > following commits?
>> > > >
>> > > > 11ed7f934cb8 (rcu: Make nocb leader kthreads process pending
>> > > > callbacks after spawning)
>> > > >
>> > > > 73a860cd58a1 (rcu: Replace flush_signals() with
>> > > > WARN_ON(signal_pending()))
>> > > >
>> > > > c847f14217d5 (rcu: Avoid misordering in nocb_leader_wait())
>> > > >
>> > > > For whatever it is worth, I am guessing this one.
>> > >
>> > > Indeed, c847f14217d5 it is.
>> > >
>> > > Much to my embarrasment I just noticed that in addition to the
>> > > rcu merge, triggering the bug "requires" my specific Fedora
>> > > rawhide network
>> > > setup. Booting in single mode and modprobe ppp_generic is fine.
>> > > The bug
>> > > appears when starting with my regular fedora network setup, which
>> > > in my case
>> > > includes 3 ethernet adapters and a libvirt birdge+nat setup.
>> > >
>> > > Hope that helps.
>> > >
>> > > I am attaching the config.
>> >
>> > It does help a lot, thank you!!!
>> >
>> > The following patch is a bit of a shot in the dark, and assumes that
>> > commit 1772947bd012 (rcu: Handle NOCB callbacks from irq-disabled
>> > idle
>> > code) introduced the problem. Does this patch fix things up?
>>
>> Unfortunately not, This is linus-tip + patch
>
>OK. Can't have everything, I guess.
>
>> INFO: task kworker/u16:6:96 blocked for more than 120 seconds.
>> Not tainted 3.18.0-rc1+ #4
>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>> kworker/u16:6 D ffff8800ca84cec0 11168 96 2 0x00000000
>> Workqueue: netns cleanup_net
>> ffff8802218339e8 0000000000000096 ffff8800ca84cec0 00000000001d5f00
>> ffff880221833fd8 00000000001d5f00 ffff880223264ec0 ffff8800ca84cec0
>> ffffffff82c52040 7fffffffffffffff ffffffff81ee2658 ffffffff81ee2650
>> Call Trace:
>> [<ffffffff8185b8e9>] schedule+0x29/0x70
>> [<ffffffff81860b0c>] schedule_timeout+0x26c/0x410
>> [<ffffffff81028bea>] ? native_sched_clock+0x2a/0xa0
>> [<ffffffff8110759c>] ? mark_held_locks+0x7c/0xb0
>> [<ffffffff81861b90>] ? _raw_spin_unlock_irq+0x30/0x50
>> [<ffffffff8110772d>] ? trace_hardirqs_on_caller+0x15d/0x200
>> [<ffffffff8185d31c>] wait_for_completion+0x10c/0x150
>> [<ffffffff810e4ed0>] ? wake_up_state+0x20/0x20
>> [<ffffffff8112a219>] _rcu_barrier+0x159/0x200
>> [<ffffffff8112a315>] rcu_barrier+0x15/0x20
>> [<ffffffff8171657f>] netdev_run_todo+0x6f/0x310
>> [<ffffffff8170b145>] ? rollback_registered_many+0x265/0x2e0
>> [<ffffffff817235ee>] rtnl_unlock+0xe/0x10
>> [<ffffffff8170cfa6>] default_device_exit_batch+0x156/0x180
>> [<ffffffff810fd390>] ? abort_exclusive_wait+0xb0/0xb0
>> [<ffffffff81705053>] ops_exit_list.isra.1+0x53/0x60
>> [<ffffffff81705c00>] cleanup_net+0x100/0x1f0
>> [<ffffffff810cca98>] process_one_work+0x218/0x850
>> [<ffffffff810cc9ff>] ? process_one_work+0x17f/0x850
>> [<ffffffff810cd1b7>] ? worker_thread+0xe7/0x4a0
>> [<ffffffff810cd13b>] worker_thread+0x6b/0x4a0
>> [<ffffffff810cd0d0>] ? process_one_work+0x850/0x850
>> [<ffffffff810d348b>] kthread+0x10b/0x130
>> [<ffffffff81028c69>] ? sched_clock+0x9/0x10
>> [<ffffffff810d3380>] ? kthread_create_on_node+0x250/0x250
>> [<ffffffff818628bc>] ret_from_fork+0x7c/0xb0
>> [<ffffffff810d3380>] ? kthread_create_on_node+0x250/0x250
>> 4 locks held by kworker/u16:6/96:
>> #0: ("%s""netns"){.+.+.+}, at: [<ffffffff810cc9ff>] process_one_work+0x17f/0x850
>> #1: (net_cleanup_work){+.+.+.}, at: [<ffffffff810cc9ff>] process_one_work+0x17f/0x850
>> #2: (net_mutex){+.+.+.}, at: [<ffffffff81705b8c>] cleanup_net+0x8c/0x1f0
>> #3: (rcu_sched_state.barrier_mutex){+.+...}, at: [<ffffffff8112a0f5>] _rcu_barrier+0x35/0x200
>> INFO: task modprobe:1045 blocked for more than 120 seconds.
>> Not tainted 3.18.0-rc1+ #4
>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>> modprobe D ffff880218343480 12920 1045 1044 0x00000080
>> ffff880218353bf8 0000000000000096 ffff880218343480 00000000001d5f00
>> ffff880218353fd8 00000000001d5f00 ffffffff81e1b580 ffff880218343480
>> ffff880218343480 ffffffff81f8f748 0000000000000246 ffff880218343480
>> Call Trace:
>> [<ffffffff8185be91>] schedule_preempt_disabled+0x31/0x80
>> [<ffffffff8185d6e3>] mutex_lock_nested+0x183/0x440
>> [<ffffffff81705a1f>] ? register_pernet_subsys+0x1f/0x50
>> [<ffffffff81705a1f>] ? register_pernet_subsys+0x1f/0x50
>> [<ffffffffa0673000>] ? 0xffffffffa0673000
>> [<ffffffff81705a1f>] register_pernet_subsys+0x1f/0x50
>> [<ffffffffa0673048>] br_init+0x48/0xd3 [bridge]
>> [<ffffffff81002148>] do_one_initcall+0xd8/0x210
>> [<ffffffff81153052>] load_module+0x20c2/0x2870
>> [<ffffffff8114e030>] ? store_uevent+0x70/0x70
>> [<ffffffff81278717>] ? kernel_read+0x57/0x90
>> [<ffffffff811539e6>] SyS_finit_module+0xa6/0xe0
>> [<ffffffff81862969>] system_call_fastpath+0x12/0x17
>> 1 lock held by modprobe/1045:
>> #0: (net_mutex){+.+.+.}, at: [<ffffffff81705a1f>] register_pernet_subsys+0x1f/0x50
>
>Presumably the kworker/u16:6 completed, then modprobe hung?
>
>If not, I have some very hard questions about why net_mutex can be
>held by two tasks concurrently, given that it does not appear to be a
>reader-writer lock...
>
>Either way, my patch assumed that 39953dfd4007 (rcu: Avoid misordering in
>__call_rcu_nocb_enqueue()) would work and that 1772947bd012 (rcu: Handle
>NOCB callbacks from irq-disabled idle code) would fail. Is that the case?
>If not, could you please bisect the commits between 11ed7f934cb8 (rcu:
>Make nocb leader kthreads process pending callbacks after spawning)
>and c847f14217d5 (rcu: Avoid misordering in nocb_leader_wait())?
Just a note to add that I am also reliably inducing what appears
to be this issue on a current -net tree, when configuring openvswitch
via script. I am available to test patches or bisect tomorrow (Friday)
US time if needed.
The stack is as follows:
[ 1320.492020] INFO: task ovs-vswitchd:1303 blocked for more than 120 seconds.
[ 1320.498965] Not tainted 3.17.0-testola+ #1
[ 1320.503570] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 1320.511374] ovs-vswitchd D ffff88013fc14600 0 1303 1302 0x00000004
[ 1320.511378] ffff8801388d77d8 0000000000000002 ffff880031144b00 ffff8801388d7fd8
[ 1320.511382] 0000000000014600 0000000000014600 ffff8800b092e400 ffff880031144b00
[ 1320.511385] ffff8800b1126000 ffffffff81c58ad0 ffffffff81c58ad8 7fffffffffffffff
[ 1320.511389] Call Trace:
[ 1320.511396] [<ffffffff81739db9>] schedule+0x29/0x70
[ 1320.511399] [<ffffffff8173cd8c>] schedule_timeout+0x1dc/0x260
[ 1320.511404] [<ffffffff8109698d>] ? check_preempt_curr+0x8d/0xa0
[ 1320.511407] [<ffffffff810969bd>] ? ttwu_do_wakeup+0x1d/0xd0
[ 1320.511410] [<ffffffff8173aab6>] wait_for_completion+0xa6/0x160
[ 1320.511413] [<ffffffff81099980>] ? wake_up_state+0x20/0x20
[ 1320.511417] [<ffffffff810cdb57>] _rcu_barrier+0x157/0x200
[ 1320.511419] [<ffffffff810cdc55>] rcu_barrier+0x15/0x20
[ 1320.511423] [<ffffffff8163a780>] netdev_run_todo+0x60/0x300
[ 1320.511427] [<ffffffff8164515e>] rtnl_unlock+0xe/0x10
[ 1320.511435] [<ffffffffa01aecc5>] internal_dev_destroy+0x55/0x80 [openvswitch]
[ 1320.511440] [<ffffffffa01ae622>] ovs_vport_del+0x32/0x40 [openvswitch]
[ 1320.511444] [<ffffffffa01a7dd0>] ovs_dp_detach_port+0x30/0x40 [openvswitch]
[ 1320.511448] [<ffffffffa01a7ea5>] ovs_vport_cmd_del+0xc5/0x110 [openvswitch]
[ 1320.511452] [<ffffffff816675b5>] genl_family_rcv_msg+0x1a5/0x3c0
[ 1320.511455] [<ffffffff816677d0>] ? genl_family_rcv_msg+0x3c0/0x3c0
[ 1320.511458] [<ffffffff81667861>] genl_rcv_msg+0x91/0xd0
[ 1320.511461] [<ffffffff816658d1>] netlink_rcv_skb+0xc1/0xe0
[ 1320.511463] [<ffffffff81665dfc>] genl_rcv+0x2c/0x40
[ 1320.511466] [<ffffffff81664e66>] netlink_unicast+0xf6/0x200
[ 1320.511468] [<ffffffff8166528d>] netlink_sendmsg+0x31d/0x780
[ 1320.511472] [<ffffffff81662274>] ? netlink_rcv_wake+0x44/0x60
[ 1320.511475] [<ffffffff816632e3>] ? netlink_recvmsg+0x1d3/0x3e0
[ 1320.511479] [<ffffffff8161c463>] sock_sendmsg+0x93/0xd0
[ 1320.511484] [<ffffffff81332d00>] ? apparmor_file_alloc_security+0x20/0x40
[ 1320.511487] [<ffffffff8162a697>] ? verify_iovec+0x47/0xd0
[ 1320.511491] [<ffffffff8161cc79>] ___sys_sendmsg+0x399/0x3b0
[ 1320.511495] [<ffffffff81254e02>] ? kernfs_seq_stop_active+0x32/0x40
[ 1320.511499] [<ffffffff8101c385>] ? native_sched_clock+0x35/0x90
[ 1320.511502] [<ffffffff8101c385>] ? native_sched_clock+0x35/0x90
[ 1320.511505] [<ffffffff8101c3e9>] ? sched_clock+0x9/0x10
[ 1320.511509] [<ffffffff81122d5c>] ? acct_account_cputime+0x1c/0x20
[ 1320.511512] [<ffffffff8109ce6b>] ? account_user_time+0x8b/0xa0
[ 1320.511516] [<ffffffff811fc135>] ? __fget_light+0x25/0x70
[ 1320.511519] [<ffffffff8161d372>] __sys_sendmsg+0x42/0x80
[ 1320.511521] [<ffffffff8161d3c2>] SyS_sendmsg+0x12/0x20
[ 1320.511525] [<ffffffff8173e6a4>] tracesys_phase2+0xd8/0xdd
-J
---
-Jay Vosburgh, jay.vosburgh@...onical.com
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