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Message-ID: <20180703043021.GA547@jagdpanzerIV>
Date:   Tue, 3 Jul 2018 13:30:21 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Tejun Heo <tj@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: printk() from NMI backtrace can delay a lot

Cc-ing Linus, Tejun, Andrew
[I'll keep the entire lockdep report]

On (07/02/18 19:26), Tetsuo Handa wrote:
[..]
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606834] swapper/0/0 is trying to acquire lock:
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606835] 00000000316e1432 (console_owner){-.-.}, at: console_unlock+0x1ce/0x8b0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606840] 
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606841] but task is already holding lock:
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606842] 000000009b45dcb4 (&(&pool->lock)->rlock){-.-.}, at: show_workqueue_state+0x3b2/0x900
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606847] 
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606848] which lock already depends on the new lock.
> ...
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606851] the existing dependency chain (in reverse order) is:
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606852] 
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606852] -> #4 (&(&pool->lock)->rlock){-.-.}:
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606857]        _raw_spin_lock+0x2a/0x40
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606858]        __queue_work+0xfb/0x780
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606859]        queue_work_on+0xde/0x110
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606861]        put_pwq+0x85/0x90
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606862]        put_pwq_unlocked.part.29+0x1d/0x30
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606863]        destroy_workqueue+0x2df/0x320
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606865]        tipc_topsrv_stop+0x1a0/0x290
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606866]        tipc_exit_net+0x15/0x40
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606867]        ops_exit_list.isra.8+0x4e/0x90
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606869]        cleanup_net+0x219/0x390
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606870]        process_one_work+0x2ec/0x800
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606871]        worker_thread+0x45/0x4d0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606872]        kthread+0x14c/0x170
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606874]        ret_from_fork+0x3a/0x50

I assume this one is

	pwq->pool->lock -> last_pool->lock ?

> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606874] 
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606875] -> #3 (&pool->lock/1){-.-.}:
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606880]        _raw_spin_lock+0x2a/0x40
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606881]        __queue_work+0xfb/0x780
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606882]        queue_work_on+0xde/0x110
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606884]        tty_flip_buffer_push+0x2f/0x40
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606885]        pty_write+0xb0/0xc0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606886]        n_tty_write+0x244/0x620
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606887]        tty_write+0x1e3/0x3f0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606888]        __vfs_write+0x54/0x270
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606890]        vfs_write+0xf0/0x230
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606891]        redirected_tty_write+0x61/0xb0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606892]        do_iter_write+0x1ce/0x220
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606893]        vfs_writev+0xb0/0x140
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606895]        do_writev+0x6d/0x120
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606896]        __x64_sys_writev+0x20/0x30
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606897]        do_syscall_64+0x81/0x260
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606899]        entry_SYSCALL_64_after_hwframe+0x49/0xbe

So #3 is

	tty_port->lock -> WQ pool->lock

> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606900] -> #2 (&(&port->lock)->rlock){-.-.}:
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606905]        _raw_spin_lock_irqsave+0x56/0x70
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606906]        tty_port_tty_get+0x20/0x60
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606907]        tty_port_default_wakeup+0x15/0x40
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606909]        tty_port_tty_wakeup+0x20/0x30
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606910]        uart_write_wakeup+0x26/0x40
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606911]        serial8250_tx_chars+0x1ae/0x2d0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606913]        serial8250_handle_irq.part.23+0x108/0x130
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606915]        serial8250_default_handle_irq+0x7a/0x90
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606916]        serial8250_interrupt+0x77/0x110
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606918]        __handle_irq_event_percpu+0x80/0x480
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606919]        handle_irq_event_percpu+0x35/0x90
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606920]        handle_irq_event+0x39/0x60
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606922]        handle_edge_irq+0xa5/0x230
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606923]        handle_irq+0xae/0x120
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606924]        do_IRQ+0x53/0x110
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606925]        ret_from_intr+0x0/0x1e
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606927]        free_unref_page_list+0x333/0x590
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606928]        release_pages+0x44a/0x5c0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606930]        free_pages_and_swap_cache+0x107/0x150
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606931]        tlb_flush_mmu_free+0x4e/0x70
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606932]        arch_tlb_finish_mmu+0x61/0xa0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606934]        tlb_finish_mmu+0x36/0x50
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606935]        exit_mmap+0x10a/0x230
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606936]        mmput+0x92/0x1c0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606937]        do_exit+0x365/0x10b0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606938]        do_group_exit+0x60/0x100
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606940]        __x64_sys_exit_group+0x1c/0x20
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606941]        do_syscall_64+0x81/0x260
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606943]        entry_SYSCALL_64_after_hwframe+0x49/0xbe

#2 is
	hard IRQ uart_port->lock -> tty_port->lock

> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606943] 
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606944] -> #1 (&port_lock_key){-.-.}:
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606948]        _raw_spin_lock_irqsave+0x56/0x70
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606950]        serial8250_console_write+0x30c/0x3b0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606951]        univ8250_console_write+0x35/0x40
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606953]        console_unlock+0x650/0x8b0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606954]        register_console+0x339/0x540
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606955]        univ8250_console_init+0x30/0x3a
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606957]        console_init+0x2c6/0x424
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606958]        start_kernel+0x466/0x61f
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606959]        x86_64_start_reservations+0x2a/0x2c
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606961]        x86_64_start_kernel+0x72/0x75
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606962]        secondary_startup_64+0xa5/0xb0

Must be
  console_sem / console_owner -> uart_port->lock ?

> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606963] 
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606963] -> #0 (console_owner){-.-.}:
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606968]        lock_acquire+0xbf/0x220
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606969]        console_unlock+0x23e/0x8b0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606970]        vprintk_emit+0x394/0x680
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606971]        vprintk_default+0x28/0x30
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606973]        vprintk_func+0x57/0xc0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606974]        printk+0x5e/0x7d
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606975]        show_workqueue_state+0x448/0x900
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606977]        wq_watchdog_timer_fn+0x1df/0x320
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606978]        call_timer_fn+0xb0/0x420
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606979]        run_timer_softirq+0x2da/0x870
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606981]        __do_softirq+0xd0/0x4fe
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606982]        irq_exit+0xd4/0xe0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606983]        smp_apic_timer_interrupt+0x9a/0x2b0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606985]        apic_timer_interrupt+0xf/0x20
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606986]        native_safe_halt+0x6/0x10
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606987]        default_idle+0x2e/0x1a0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606988]        arch_cpu_idle+0x10/0x20
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606990]        default_idle_call+0x1e/0x40
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606991]        do_idle+0x205/0x2e0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606992]        cpu_startup_entry+0x6e/0x70
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606993]        rest_init+0xc7/0xd0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606995]        start_kernel+0x5fc/0x61f
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606996]        x86_64_start_reservations+0x2a/0x2c
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606997]        x86_64_start_kernel+0x72/0x75
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606999]        secondary_startup_64+0xa5/0xb0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.606999] 

#0 is
	softirq WQ pool->lock -> console_sem / console_owner -> uart_port->lock

> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607001] other info that might help us debug this:
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607001] 
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607002] Chain exists of:
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607003]   console_owner --> &pool->lock/1 --> &(&pool->lock)->rlock

I don't quite understand how that direct "console_owner -> pool->lock" is
possible, there should be uart/tty somewhere in between. For instance:

	console_owner -> uart_port->lock -> pool->lock -> &(&pool->lock)->rlock


But anyway. So we can have [but I'm not completely sure. Maybe lockdep has
something else on its mind] something like this:

	CPU1					CPU0

	#IRQ					#soft irq
	serial8250_handle_irq()			wq_watchdog_timer_fn()
	 spin_lock(&uart_port->lock)		 show_workqueue_state()
	  serial8250_rx_chars()			   spin_lock(&pool->lock)
	   tty_flip_buffer_push()		    printk()
	    tty_schedule_flip()			     serial8250_console_write()
	     queue_work()			      spin_lock(&uart_port->lock)
	      __queue_work()
	       spin_lock(&pool->lock)

We need to break the pool->lock -> uart_port->lock chain.

- use printk_deferred() to show WQs states [show_workqueue_state() is
  a timer callback, so local IRQs are enabled]. But show_workqueue_state()
  is also available via sysrq.

- what Alan Cox suggested: use spin_trylock() in serial8250_console_write()
  and just discard (do not print anything on console) console->writes() that
  can deadlock us [uart_port->lock is already locked]. This basically means
  that sometimes there will be no output on a serial console, or there
  will be missing line. Which kind of contradicts the purpose of print
  out.

We are facing the risk of no output on serial consoles in both case. Thus
there must be some other way out of this.

Any thoughts?


> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607009] 
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607010]  Possible unsafe locking scenario:
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607011] 
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607012]        CPU0                    CPU1
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607014]        ----                    ----
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607014]   lock(&(&pool->lock)->rlock);
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607017]                                lock(&pool->lock/1);
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607021]                                lock(&(&pool->lock)->rlock);
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607024]   lock(console_owner);
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607026] 
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607027]  *** DEADLOCK ***
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607027] 
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607028] 4 locks held by swapper/0/0:
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607029]  #0: 00000000acb744a0 ((&wq_watchdog_timer)){+.-.}, at: call_timer_fn+0x0/0x420
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607034]  #1: 00000000918be876 (rcu_read_lock_sched){....}, at: show_workqueue_state+0x0/0x900
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607040]  #2: 000000009b45dcb4 (&(&pool->lock)->rlock){-.-.}, at: show_workqueue_state+0x3b2/0x900
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607045]  #3: 000000005fd39989 (console_lock){+.+.}, at: vprintk_emit+0x386/0x680
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607050] 
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607051] stack backtrace:
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607053] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G           O      4.18.0-rc3 #643
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607056] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 05/19/2017
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607057] Call Trace:
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607058]  <IRQ>
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607059]  dump_stack+0xe9/0x148
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607061]  print_circular_bug.isra.39+0x1f3/0x201
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607062]  __lock_acquire+0x135f/0x1400
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607063]  lock_acquire+0xbf/0x220
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607065]  ? console_unlock+0x215/0x8b0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607066]  ? lock_acquire+0xbf/0x220
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607067]  ? console_unlock+0x1ce/0x8b0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607068]  console_unlock+0x23e/0x8b0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607070]  ? console_unlock+0x1ce/0x8b0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607071]  vprintk_emit+0x394/0x680
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607072]  vprintk_default+0x28/0x30
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607073]  vprintk_func+0x57/0xc0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607074]  printk+0x5e/0x7d
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607076]  show_workqueue_state+0x448/0x900
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607077]  ? wq_watchdog_timer_fn+0x1a6/0x320
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607078]  wq_watchdog_timer_fn+0x1df/0x320
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607080]  ? show_workqueue_state+0x900/0x900
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607081]  ? show_workqueue_state+0x900/0x900
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607082]  call_timer_fn+0xb0/0x420
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607084]  ? show_workqueue_state+0x900/0x900
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607085]  run_timer_softirq+0x2da/0x870
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607086]  __do_softirq+0xd0/0x4fe
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607087]  irq_exit+0xd4/0xe0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607089]  smp_apic_timer_interrupt+0x9a/0x2b0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607090]  apic_timer_interrupt+0xf/0x20
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607091]  </IRQ>
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607092] RIP: 0010:native_safe_halt+0x6/0x10
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607093] Code: 53 18 fe 65 48 8b 04 25 40 5e 01 00 f0 80 48 02 20 48 8b 00 a8 08 0f 84 57 ff ff ff eb a6 90 90 90 90 90 90 55 48 89 e5 fb f4 <5d> c3 0f 1f 84 00 00 00 00 00 55 48 89 e5 f4 5d c3 90 90 90 90 90 
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607135] RSP: 0018:ffffffff84003df8 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff13
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607138] RAX: ffffffff8406d7c0 RBX: 0000000000000000 RCX: 0000000000000000
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607140] RDX: ffffffff8406d7c0 RSI: 0000000000000001 RDI: ffffffff8406d7c0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607142] RBP: ffffffff84003df8 R08: 0000000000000001 R09: 0000000000000000
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607144] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607146] R13: 0000000000000000 R14: 0000000000000000 R15: ffffffff84098920
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607148]  ? trace_hardirqs_on+0xd/0x10
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607149]  default_idle+0x2e/0x1a0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607150]  arch_cpu_idle+0x10/0x20
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607151]  default_idle_call+0x1e/0x40
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607152]  do_idle+0x205/0x2e0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607154]  ? do_idle+0xf9/0x2e0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607155]  cpu_startup_entry+0x6e/0x70
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607156]  rest_init+0xc7/0xd0
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607158]  ? trace_event_define_fields_vector_alloc_managed+0x8b/0x8b
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607159]  start_kernel+0x5fc/0x61f
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607161]  x86_64_start_reservations+0x2a/0x2c
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607162]  x86_64_start_kernel+0x72/0x75
> 2018-07-02 12:13:13 192.168.159.129:6666 [  151.607163]  secondary_startup_64+0xa5/0xb0
> 2018-07-02 12:13:44 192.168.159.129:6666 [  182.238928] BUG: workqueue lockup - pool cpus=2 node=0 flags=0x0 nice=0 stuck for 92s!
> 2018-07-02 12:13:44 192.168.159.129:6666 [  182.241803] Showing busy workqueues and worker pools:
> 2018-07-02 12:13:44 192.168.159.129:6666 [  182.243616] workqueue mm_percpu_wq: flags=0x8
> 2018-07-02 12:13:44 192.168.159.129:6666 [  182.245141]   pwq 4: cpus=2 node=0 flags=0x0 nice=0 active=1/256
> 2018-07-02 12:13:44 192.168.159.129:6666 [  182.247130]     pending: vmstat_update
> 2018-07-02 12:14:11 192.168.159.129:6666 [  209.030165] INFO: rcu_sched detected stalls on CPUs/tasks:
> 2018-07-02 12:14:11 192.168.159.129:6666 [  209.032175] 	2-...0: (0 ticks this GP) idle=0be/1/4611686018427387904 softirq=5544/5544 fqs=27833 
> 2018-07-02 12:14:11 192.168.159.129:6666 [  209.035069] 	(detected by 3, t=120007 jiffies, g=2553, c=2552, q=1155)
> 2018-07-02 12:14:11 192.168.159.129:6666 [  209.037220] Sending NMI from CPU 3 to CPUs 2:

	-ss

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