Re: localed stuck in recent 3.18 git in copy_net_ns?

From: Yanko Kaneti
Date: Sat Oct 25 2014 - 15:16:26 EST

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In reply to: Paul E. McKenney: "Re: localed stuck in recent 3.18 git in copy_net_ns?"
Next in thread: Paul E. McKenney: "Re: localed stuck in recent 3.18 git in copy_net_ns?"
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On Fri-10/24/14-2014 14:49, Paul E. McKenney wrote:
> On Sat, Oct 25, 2014 at 12:25:57AM +0300, Yanko Kaneti wrote:
> > On Fri-10/24/14-2014 11:32, Paul E. McKenney wrote:
> > > On Fri, Oct 24, 2014 at 08:35:26PM +0300, Yanko Kaneti wrote:
> > > > On Fri-10/24/14-2014 10:20, Paul E. McKenney wrote:
>
> [ . . . ]
>
> > > > > Well, if you are feeling aggressive, give the following patch a spin.
> > > > > I am doing sanity tests on it in the meantime.
> > > >
> > > > Doesn't seem to make a difference here
> > >
> > > OK, inspection isn't cutting it, so time for tracing. Does the system
> > > respond to user input? If so, please enable rcu:rcu_barrier ftrace before
> > > the problem occurs, then dump the trace buffer after the problem occurs.
> >
> > Sorry for being unresposive here, but I know next to nothing about tracing
> > or most things about the kernel, so I have some cathing up to do.
> >
> > In the meantime some layman observations while I tried to find what exactly
> > triggers the problem.
> > - Even in runlevel 1 I can reliably trigger the problem by starting libvirtd
> > - libvirtd seems to be very active in using all sorts of kernel facilities
> > that are modules on fedora so it seems to cause many simultaneous kworker
> > calls to modprobe
> > - there are 8 kworker/u16 from 0 to 7
> > - one of these kworkers always deadlocks, while there appear to be two
> > kworker/u16:6 - the seventh
>
> Adding Tejun on CC in case this duplication of kworker/u16:6 is important.
>
> > 6 vs 8 as in 6 rcuos where before they were always 8
> >
> > Just observations from someone who still doesn't know what the u16
> > kworkers are..
>
> Could you please run the following diagnostic patch? This will help
> me see if I have managed to miswire the rcuo kthreads. It should
> print some information at task-hang time.

So here the output with todays linux tip and the diagnostic patch.
This is the case with just starting libvird in runlevel 1.
Also a snapshot of the kworker/u16 s

6 ? S 0:00 \_ [kworker/u16:0]
553 ? S 0:00 | \_ [kworker/u16:0]
554 ? D 0:00 | \_ /sbin/modprobe -q -- bridge
78 ? S 0:00 \_ [kworker/u16:1]
92 ? S 0:00 \_ [kworker/u16:2]
93 ? S 0:00 \_ [kworker/u16:3]
94 ? S 0:00 \_ [kworker/u16:4]
95 ? S 0:00 \_ [kworker/u16:5]
96 ? D 0:00 \_ [kworker/u16:6]
105 ? S 0:00 \_ [kworker/u16:7]
108 ? S 0:00 \_ [kworker/u16:8]

INFO: task kworker/u16:6:96 blocked for more than 120 seconds.
Not tainted 3.18.0-rc1+ #16
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u16:6 D ffff8800ca9ecec0 11552 96 2 0x00000000
Workqueue: netns cleanup_net
ffff880221fff9c8 0000000000000096 ffff8800ca9ecec0 00000000001d5f00
ffff880221ffffd8 00000000001d5f00 ffff880223260000 ffff8800ca9ecec0
ffffffff82c44010 7fffffffffffffff ffffffff81ee3798 ffffffff81ee3790
Call Trace:
[<ffffffff81866219>] schedule+0x29/0x70
[<ffffffff8186b43c>] schedule_timeout+0x26c/0x410
[<ffffffff81028bea>] ? native_sched_clock+0x2a/0xa0
[<ffffffff8110748c>] ? mark_held_locks+0x7c/0xb0
[<ffffffff8186c4c0>] ? _raw_spin_unlock_irq+0x30/0x50
[<ffffffff8110761d>] ? trace_hardirqs_on_caller+0x15d/0x200
[<ffffffff81867c4c>] wait_for_completion+0x10c/0x150
[<ffffffff810e4dc0>] ? wake_up_state+0x20/0x20
[<ffffffff81133627>] _rcu_barrier+0x677/0xcd0
[<ffffffff81133cd5>] rcu_barrier+0x15/0x20
[<ffffffff81720edf>] netdev_run_todo+0x6f/0x310
[<ffffffff81715aa5>] ? rollback_registered_many+0x265/0x2e0
[<ffffffff8172df4e>] rtnl_unlock+0xe/0x10
[<ffffffff81717906>] default_device_exit_batch+0x156/0x180
[<ffffffff810fd280>] ? abort_exclusive_wait+0xb0/0xb0
[<ffffffff8170f9b3>] ops_exit_list.isra.1+0x53/0x60
[<ffffffff81710560>] cleanup_net+0x100/0x1f0
[<ffffffff810cc988>] process_one_work+0x218/0x850
[<ffffffff810cc8ef>] ? process_one_work+0x17f/0x850
[<ffffffff810cd0a7>] ? worker_thread+0xe7/0x4a0
[<ffffffff810cd02b>] worker_thread+0x6b/0x4a0
[<ffffffff810ccfc0>] ? process_one_work+0x850/0x850
[<ffffffff810d337b>] kthread+0x10b/0x130
[<ffffffff81028c69>] ? sched_clock+0x9/0x10
[<ffffffff810d3270>] ? kthread_create_on_node+0x250/0x250
[<ffffffff8186d1fc>] ret_from_fork+0x7c/0xb0
[<ffffffff810d3270>] ? kthread_create_on_node+0x250/0x250
4 locks held by kworker/u16:6/96:
#0: ("%s""netns"){.+.+.+}, at: [<ffffffff810cc8ef>]
#process_one_work+0x17f/0x850
#1: (net_cleanup_work){+.+.+.}, at: [<ffffffff810cc8ef>]
#process_one_work+0x17f/0x850
#2: (net_mutex){+.+.+.}, at: [<ffffffff817104ec>] cleanup_net+0x8c/0x1f0
#3: (rcu_sched_state.barrier_mutex){+.+...}, at: [<ffffffff81133025>]
#_rcu_barrier+0x75/0xcd0
rcu_show_nocb_setup(): rcu_sched nocb state:
0: ffff8802267ced40 l:ffff8802267ced40 n:ffff8802269ced40 .G.
1: ffff8802269ced40 l:ffff8802267ced40 n: (null) ...
2: ffff880226bced40 l:ffff880226bced40 n:ffff880226dced40 .G.
3: ffff880226dced40 l:ffff880226bced40 n: (null) N..
4: ffff880226fced40 l:ffff880226fced40 n:ffff8802271ced40 .G.
5: ffff8802271ced40 l:ffff880226fced40 n: (null) ...
6: ffff8802273ced40 l:ffff8802273ced40 n:ffff8802275ced40 N..
7: ffff8802275ced40 l:ffff8802273ced40 n: (null) N..
rcu_show_nocb_setup(): rcu_bh nocb state:
0: ffff8802267ceac0 l:ffff8802267ceac0 n:ffff8802269ceac0 ...
1: ffff8802269ceac0 l:ffff8802267ceac0 n: (null) ...
2: ffff880226bceac0 l:ffff880226bceac0 n:ffff880226dceac0 ...
3: ffff880226dceac0 l:ffff880226bceac0 n: (null) ...
4: ffff880226fceac0 l:ffff880226fceac0 n:ffff8802271ceac0 ...
5: ffff8802271ceac0 l:ffff880226fceac0 n: (null) ...
6: ffff8802273ceac0 l:ffff8802273ceac0 n:ffff8802275ceac0 ...
7: ffff8802275ceac0 l:ffff8802273ceac0 n: (null) ...
INFO: task modprobe:554 blocked for more than 120 seconds.
Not tainted 3.18.0-rc1+ #16
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
modprobe D ffff8800c85dcec0 12456 554 553 0x00000000
ffff8802178afbf8 0000000000000096 ffff8800c85dcec0 00000000001d5f00
ffff8802178affd8 00000000001d5f00 ffffffff81e1b580 ffff8800c85dcec0
ffff8800c85dcec0 ffffffff81f90c08 0000000000000246 ffff8800c85dcec0
Call Trace:
[<ffffffff818667c1>] schedule_preempt_disabled+0x31/0x80
[<ffffffff81868013>] mutex_lock_nested+0x183/0x440
[<ffffffff8171037f>] ? register_pernet_subsys+0x1f/0x50
[<ffffffff8171037f>] ? register_pernet_subsys+0x1f/0x50
[<ffffffffa0619000>] ? 0xffffffffa0619000
[<ffffffff8171037f>] register_pernet_subsys+0x1f/0x50
[<ffffffffa0619048>] br_init+0x48/0xd3 [bridge]
[<ffffffff81002148>] do_one_initcall+0xd8/0x210
[<ffffffff8115bc22>] load_module+0x20c2/0x2870
[<ffffffff81156c00>] ? store_uevent+0x70/0x70
[<ffffffff81281327>] ? kernel_read+0x57/0x90
[<ffffffff8115c5b6>] SyS_finit_module+0xa6/0xe0
[<ffffffff8186d2d5>] ? sysret_check+0x22/0x5d
[<ffffffff8186d2a9>] system_call_fastpath+0x12/0x17
1 lock held by modprobe/554:
#0: (net_mutex){+.+.+.}, at: [<ffffffff8171037f>]
#register_pernet_subsys+0x1f/0x50
rcu_show_nocb_setup(): rcu_sched nocb state:
0: ffff8802267ced40 l:ffff8802267ced40 n:ffff8802269ced40 .G.
1: ffff8802269ced40 l:ffff8802267ced40 n: (null) ...
2: ffff880226bced40 l:ffff880226bced40 n:ffff880226dced40 .G.
3: ffff880226dced40 l:ffff880226bced40 n: (null) N..
4: ffff880226fced40 l:ffff880226fced40 n:ffff8802271ced40 .G.
5: ffff8802271ced40 l:ffff880226fced40 n: (null) ...
6: ffff8802273ced40 l:ffff8802273ced40 n:ffff8802275ced40 N..
7: ffff8802275ced40 l:ffff8802273ced40 n: (null) N..
rcu_show_nocb_setup(): rcu_bh nocb state:
0: ffff8802267ceac0 l:ffff8802267ceac0 n:ffff8802269ceac0 ...
1: ffff8802269ceac0 l:ffff8802267ceac0 n: (null) ...
2: ffff880226bceac0 l:ffff880226bceac0 n:ffff880226dceac0 ...
3: ffff880226dceac0 l:ffff880226bceac0 n: (null) ...
4: ffff880226fceac0 l:ffff880226fceac0 n:ffff8802271ceac0 ...
5: ffff8802271ceac0 l:ffff880226fceac0 n: (null) ...
6: ffff8802273ceac0 l:ffff8802273ceac0 n:ffff8802275ceac0 ...
7: ffff8802275ceac0 l:ffff8802273ceac0 n: (null) ...

> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> rcu: Dump no-CBs CPU state at task-hung time
>
> Strictly diagnostic commit for rcu_barrier() hang. Not for inclusion.
>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
>
> diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
> index 0e5366200154..34048140577b 100644
> --- a/include/linux/rcutiny.h
> +++ b/include/linux/rcutiny.h
> @@ -157,4 +157,8 @@ static inline bool rcu_is_watching(void)
>
> #endif /* #else defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
>
> +static inline void rcu_show_nocb_setup(void)
> +{
> +}
> +
> #endif /* __LINUX_RCUTINY_H */
> diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
> index 52953790dcca..0b813bdb971b 100644
> --- a/include/linux/rcutree.h
> +++ b/include/linux/rcutree.h
> @@ -97,4 +97,6 @@ extern int rcu_scheduler_active __read_mostly;
>
> bool rcu_is_watching(void);
>
> +void rcu_show_nocb_setup(void);
> +
> #endif /* __LINUX_RCUTREE_H */
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index 06db12434d72..e6e4d0f6b063 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -118,6 +118,7 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
> " disables this message.\n");
> sched_show_task(t);
> debug_show_held_locks(t);
> + rcu_show_nocb_setup();
>
> touch_nmi_watchdog();
>
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index 240fa9094f83..6b373e79ce0e 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -1513,6 +1513,7 @@ rcu_torture_cleanup(void)
> {
> int i;
>
> + rcu_show_nocb_setup();
> rcutorture_record_test_transition();
> if (torture_cleanup_begin()) {
> if (cur_ops->cb_barrier != NULL)
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 927c17b081c7..285b3f6fb229 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -2699,6 +2699,31 @@ static bool init_nocb_callback_list(struct rcu_data *rdp)
>
> #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
>
> +void rcu_show_nocb_setup(void)
> +{
> +#ifdef CONFIG_RCU_NOCB_CPU
> + int cpu;
> + struct rcu_data *rdp;
> + struct rcu_state *rsp;
> +
> + for_each_rcu_flavor(rsp) {
> + pr_alert("rcu_show_nocb_setup(): %s nocb state:\n", rsp->name);
> + for_each_possible_cpu(cpu) {
> + if (!rcu_is_nocb_cpu(cpu))
> + continue;
> + rdp = per_cpu_ptr(rsp->rda, cpu);
> + pr_alert("%3d: %p l:%p n:%p %c%c%c\n",
> + cpu,
> + rdp, rdp->nocb_leader, rdp->nocb_next_follower,
> + ".N"[!!rdp->nocb_head],
> + ".G"[!!rdp->nocb_gp_head],
> + ".F"[!!rdp->nocb_follower_head]);
> + }
> + }
> +#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
> +}
> +EXPORT_SYMBOL_GPL(rcu_show_nocb_setup);
> +
> /*
> * An adaptive-ticks CPU can potentially execute in kernel mode for an
> * arbitrarily long period of time with the scheduling-clock tick turned
>
--
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