WARNING: possible circular locking dependency detected

[Qian Cai <cai@gmx.us>]

Compiling kernel on an aarch64 server with the latest mainline (rc2) generated this,

[  910.263839] WARNING: possible circular locking dependency detected
[  910.263841] 4.20.0-rc2+ #4 Tainted: G        W    L   
[  910.263843] ------------------------------------------------------
[  910.263844] swapper/0/0 is trying to acquire lock:
+0x3f0/0x8806] 0000000071c616d1 (console_owner){-.-.}, at: console_unlock+0x26cc481d4 (&pool->ldy depends on therse order) is:
[ 0.263880]        __queue_work+0x1dc/0xb78
[  910.263882]        queue_work_on+0x140/0x158
[  910.263883]        tty_flip_buffer_push+0xd8/0x108
[  910.263885]        pty_write+0xf8/0x100
[  910.263886]        n_tty_write+0x2d8/0x698
[  910.263888]        tty_write+0x254/0x410
[  910.263889]        __vfs_write+0xd4/0x330
[  910.263891]        vfs_write+0xd8/0x240
[  910.263892]        redirected_tty_write+0x74/0xd0
[  910.263894]        do_iter_write+0x224/0x270
[  910.263895]        vfs_writev+0x114/0x1d8
[  910.263897]        do_writev+0xd8/0x1e0
[  910.263898]        __arm64_sys_writev+0x50/0x60
[  910.263900]        el0_svc_handler+0xd4/0x198
[  910.263901]        el0_svc+0x8/0xc
[  910.263902] 
[  910.263903] -> #2 (&(&port->lock)->rlock){-.-.}:
[  910.263908]        __lock_acquire+0x3f0/0x880
[  910.263910]        lock_acquire+0x1a8/0x430
[  910.263911]        _raw_spin_lock_irqsave+0x74/0x98
[  910.263913]        tty_port_tty_get+0x28/0x68
[  910.263915]        tty_port_default_wakeup+0x20/0x40
[  910.263916]        tty_port_tty_wakeup+0x38/0x48
[  910.263918]        uart_write_wakeup+0x2c/0x40
[  910.263919]        pl011_tx_chars+0x2a4/0x358
[  910.263921]        pl011_start_tx_pio+0x24/0xa8
[  910.263922]        pl011_start_tx+0x150/0x2c0
[  910.263924]        __uart_start.isra.1+0x84/0x90
[  910.263925]        uart_write+0x1ec/0x2d8
[  910.263927]        do_output_char+0x1c4/0x2a8
[  910.263928]        n_tty_write+0x338/0x698
[  910.263930]        tty_write+0x254/0x410
[  910.263931]        redirected_tty_write+0xb4/0xd0
[  910.263933]        do_iter_write+0x224/0x270
[  910.263934]        vfs_writev+0x114/0x1d8
[  910.263935]        do_writev+0xd8/0x1e0
[  910.263937]        __arm64_sys_writev+0x50/0x60
[  910.263939]        el0_svc_handler+0xd4/0x198
[  910.263940]        el0_svc+0x8/0xc
[  910.263941] 
[  910.263942] -> #1 (&port_lock_key){-.-.}:
[  910.263947]        __lock_acquire+0x3f0/0x880
[  910.263949]        lock_acquire+0x1a8/0x430
[  910.263950]        _raw_spin_lock+0x68/0x88
[  910.263952]        pl011_console_write+0x1d8/0x258
[  910.263953]        console_unlock+0x3ac/0x938
[  910.263955]        register_console+0x360/0x4c8
[  910.263956]        uart_add_one_port+0x798/0x870
[  910.263958]        pl011_register_port+0x98/0x128
[  910.263959]        sbsa_uart_probe+0x320/0x3b0
[  910.263961]        platform_drv_probe+0x74/0xd0
[  910.263962]        really_probe+0x424/0x678
[  910.263964]        driver_probe_device+0x130/0x1a0
[  910.263966]        __device_attach_driver+0x10c/0x188
[  910.263967]        bus_for_each_drv+0xf8/0x158
[  910.263969]        __device_attach+0x188/0x230
[  910.263970]        device_initial_probe+0x24/0x30
[  910.263972]        bus_probe_device+0xf0/0x100
[  910.263973]        device_add+0x57c/0x9d8
[  910.263975]        platform_device_add+0x198/0x388
[  910.263977]        platform_device_register_full+0x16c/0x1e8
[  910.263978]        acpi_create_platform_device+0x368/0x450
[  910.263980]        acpi_default_enumeration+0x34/0x78
[  910.263982]        acpi_bus_attach+0x2dc/0x3e0
[  910.263983]        acpi_bus_attach+0x108/0x3e0
[  910.263985]        acpi_bus_attach+0x108/0x3e0
[  910.263986]        acpi_bus_attach+0x108/0x3e0
[  910.263987]        acpi_bus_scan+0xb0/0x110
[  910.263989]        acpi_scan_init+0x1a8/0x410
[  910.263990]        acpi_init+0x3e8/0x47c
[  910.263992]        do_one_initcall+0x160/0x6bc
[  910.263993]        kernel_init_freeable+0x74c/0x814
[  910.263995]        kernel_init+0x18/0x11c
[  910.263996]        ret_from_fork+0x10/0x1c
[  910.263997] 
[  910.263998] -> #0 (console_owner){-.-.}:
[  910.264004]        validate_chain.isra.17+0x998/0x1550
[  910.264005]        __lock_acquire+0x3f0/0x880
[  910.264007]        lock_acquire+0x1a8/0x430
[  910.264008]        console_unlock+0x2c8/0x938
[  910.264010]        vprintk_emit+0x358/0x5c0
[  910.264011]        vprintk_default+0x60/0xa8
[  910.264013]        vprintk_func+0x244/0x370
[  910.264014]        printk+0xc8/0xf8
[  910.264016]        show_workqueue_state+0x534/0xce0
[  910.264018]        wq_watchdog_timer_fn+0x444/0x518
[  910.264019]        call_timer_fn+0x1c4/0x708
[  910.264021]        expire_timers+0x32c/0x448
[  910.264022]        run_timer_softirq+0x290/0x328
[  910.264024]        __do_softirq+0x248/0x9c8
[  910.264025]        irq_exit+0x25c/0x2f0
[  910.264027]        __handle_domain_irq+0x8c/0xf0
[  910.264028]        gic_handle_irq+0xc0/0x168
[  910.264029]        el1_irq+0xb4/0x140
[  910.264031]        cpuidle_enter_state+0x150/0x6a0
[  910.264032]        cpuidle_enter+0x34/0x48
[  910.264034]        call_cpuidle+0x4c/0x78
[  910.264035]        do_idle+0x328/0x360
[  910.264037]        cpu_startup_entry+0x2c/0x30
[  910.264038]        rest_init+0x248/0x31c
[  910.264040]        arch_call_rest_init+0x14/0x1c
[  910.264041]        start_kernel+0x568/0x5a8
[  910.264042] 
[  910.264044] other info that might help us debug this:
[  910.264045] 
[  910.264046] Chain exists of:
[  910.264047]   console_owner --> &(&port->lock)->rlock --> &pool->lock/1
[  910.264055] 
[  910.264057]  Possible unsafe locking scenario:
[  910.264058] 
[  910.264059]        CPU0                    CPU1
[  910.264061]        ----                    ----
[  910.264062]   lock(&pool->lock/1);
[  910.264066]                                lock(&(&port->lock)->rlock);
[  910.264070]                                lock(&pool->lock/1);
[  910.264073]   lock(console_owner);
[  910.264076] 
[  910.264078]  *** DEADLOCK ***
[  910.264079] 
[  910.264080] 4 locks held by swapper/0/0:
[  910.264081]  #0: 00000000c45a46a0 ((&wq_watchdog_timer)){+.-.}, at: call_timer_fn+0x0/0x708
[  910.264087]  #1: 00000000f6706545 (rcu_read_lock_sched){....}, at: show_workqueue_state+0x0/0xce0
[  910.264094]  #2: 00000000f2c481d4 (&pool->lock/1){-.-.}, at: show_workqueue_state+0x468/0xce0
[  910.264101]  #3: 0000000014da44b5 (console_lock){+.+.}, at: vprintk_emit+0x350/0x5c0
[  910.264107] 
[  910.264108] stack backtrace:
[  910.264110] CPU: 0 PID: 0 Comm: swapper/0 Kdump: loaded Tainted: G        W    L    4.20.0-rc2+ #4
[  910.264113] Hardware name: HPE Apollo 70             /C01_APACHE_MB         , BIOS L50_5.13_1.0.6 07/10/2018
[  910.264114] Call trace:
[  910.264116]  dump_backtrace+0x0/0x2c8
[  910.264117]  show_stack+0x24/0x30
[  910.264118]  dump_stack+0x118/0x19c
[  910.264120]  print_circular_bug.isra.13+0x360/0x408
[  910.264121]  check_prev_add.constprop.22+0x690/0xa10
[  910.264123]  validate_chain.isra.17+0x998/0x1550
[  910.264124]  __lock_acquire+0x3f0/0x880
[  910.264126]  lock_acquire+0x1a8/0x430
[  910.264127]  console_unlock+0x2c8/0x938
[  910.264129]  vprintk_emit+0x358/0x5c0
[  910.264130]  vprintk_default+0x60/0xa8
[  910.264131]  vprintk_func+0x244/0x370
[  910.264133]  printk+0xc8/0xf8
[  910.264134]  show_workqueue_state+0x534/0xce0
[  910.264136]  wq_watchdog_timer_fn+0x444/0x518
[  910.264137]  call_timer_fn+0x1c4/0x708
[  910.264138]  expire_timers+0x32c/0x448
[  910.264140]  run_timer_softirq+0x290/0x328
[  910.264141]  __do_softirq+0x248/0x9c8
[  910.264143]  irq_exit+0x25c/0x2f0
[  910.264144]  __handle_domain_irq+0x8c/0xf0
[  910.264146]  gic_handle_irq+0xc0/0x168
[  910.264147]  el1_irq+0xb4/0x140
[  910.264148]  cpuidle_enter_state+0x150/0x6a0
[  910.264150]  cpuidle_enter+0x34/0x48
[  910.264151]  call_cpuidle+0x4c/0x78
[  910.264152]  do_idle+0x328/0x360
[  910.264154]  cpu_startup_entry+0x2c/0x30
[  910.264155]  rest_init+0x248/0x31c
[  910.264157]  arch_call_rest_init+0x14/0x1c
[  910.264158]  start_kernel+0x568/0x5a8
[  910.327979] ------------[ cut here ]------------