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SubjectRe: 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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