L1TF CPU bug present and SMT on, data leak possible. See CVE-2018-3646 and https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/l1tf.html for details.
hrtimer: interrupt took 32015 ns
kvm: emulating exchange as write
BUG: workqueue lockup - pool cpus=1 node=0 flags=0x0 nice=0 stuck for 164s!
Showing busy workqueues and worker pools:
workqueue events: flags=0x0
  pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=1/256 refcnt=2
    pending: cache_reap

======================================================
WARNING: possible circular locking dependency detected
4.19.109-syzkaller #0 Not tainted
------------------------------------------------------
swapper/0/0 is trying to acquire lock:
000000007fd5f0b9 (console_owner){-.-.}, at: log_next kernel/printk/printk.c:499 [inline]
000000007fd5f0b9 (console_owner){-.-.}, at: console_unlock+0x3f4/0xfe0 kernel/printk/printk.c:2416

but task is already holding lock:
000000004837dceb (&(&pool->lock)->rlock){-.-.}, at: show_workqueue_state.cold+0x7f9/0x1059 kernel/workqueue.c:4582

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&(&pool->lock)->rlock){-.-.}:
       spin_lock include/linux/spinlock.h:329 [inline]
       __queue_work+0x23c/0x1070 kernel/workqueue.c:1417
       queue_work_on+0x17e/0x1f0 kernel/workqueue.c:1486
       queue_work include/linux/workqueue.h:512 [inline]
       schedule_work include/linux/workqueue.h:570 [inline]
       put_pwq kernel/workqueue.c:1090 [inline]
       put_pwq+0x15a/0x1b0 kernel/workqueue.c:1075
       put_pwq_unlocked.part.0+0x30/0x70 kernel/workqueue.c:1107
       put_pwq_unlocked kernel/workqueue.c:1101 [inline]
       destroy_workqueue+0x5f4/0x6f0 kernel/workqueue.c:4241
       do_floppy_init drivers/block/floppy.c:4737 [inline]
       floppy_async_init+0x1f0a/0x2043 drivers/block/floppy.c:4754
       async_run_entry_fn+0x121/0x530 kernel/async.c:127
       process_one_work+0x91f/0x1640 kernel/workqueue.c:2153
       worker_thread+0x96/0xe20 kernel/workqueue.c:2296
       kthread+0x34a/0x420 kernel/kthread.c:246
       ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

-> #3 (&pool->lock/1){..-.}:
       spin_lock include/linux/spinlock.h:329 [inline]
       __queue_work+0x23c/0x1070 kernel/workqueue.c:1417
       queue_work_on+0x17e/0x1f0 kernel/workqueue.c:1486
       pty_write+0x198/0x1f0 drivers/tty/pty.c:125
       n_tty_write+0xa69/0x1080 drivers/tty/n_tty.c:2354
       do_tty_write drivers/tty/tty_io.c:960 [inline]
       tty_write+0x452/0x790 drivers/tty/tty_io.c:1044
       __vfs_write+0xf7/0x760 fs/read_write.c:485
       vfs_write+0x206/0x550 fs/read_write.c:549
       ksys_write+0x12b/0x2a0 fs/read_write.c:599
       do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #2 (&(&port->lock)->rlock){-.-.}:
       tty_port_tty_get+0x1d/0x80 drivers/tty/tty_port.c:289
       tty_port_default_wakeup+0x11/0x40 drivers/tty/tty_port.c:47
       serial8250_tx_chars+0x48f/0xae0 drivers/tty/serial/8250/8250_port.c:1806
       serial8250_handle_irq.part.0+0x24b/0x290 drivers/tty/serial/8250/8250_port.c:1879
       serial8250_handle_irq drivers/tty/serial/8250/8250_port.c:1865 [inline]
       serial8250_default_handle_irq+0xb5/0x140 drivers/tty/serial/8250/8250_port.c:1895
       serial8250_interrupt+0xf2/0x1d0 drivers/tty/serial/8250/8250_core.c:125
       __handle_irq_event_percpu+0x144/0x8e0 kernel/irq/handle.c:149
       handle_irq_event_percpu+0x76/0x160 kernel/irq/handle.c:189
       handle_irq_event+0xa2/0x12d kernel/irq/handle.c:206
       handle_edge_irq+0x24b/0x8c0 kernel/irq/chip.c:797
       generic_handle_irq_desc include/linux/irqdesc.h:155 [inline]
       handle_irq+0x35/0x50 arch/x86/kernel/irq_64.c:87
       do_IRQ+0x93/0x1c0 arch/x86/kernel/irq.c:246
       ret_from_intr+0x0/0x1e
       arch_local_irq_restore arch/x86/include/asm/paravirt.h:789 [inline]
       __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160 [inline]
       _raw_spin_unlock_irqrestore+0x91/0xe0 kernel/locking/spinlock.c:184
       spin_unlock_irqrestore include/linux/spinlock.h:384 [inline]
       uart_write+0x365/0x680 drivers/tty/serial/serial_core.c:612
       process_output_block drivers/tty/n_tty.c:593 [inline]
       n_tty_write+0x3ee/0x1080 drivers/tty/n_tty.c:2331
       do_tty_write drivers/tty/tty_io.c:960 [inline]
       tty_write+0x452/0x790 drivers/tty/tty_io.c:1044
       redirected_tty_write+0xaa/0xb0 drivers/tty/tty_io.c:1065
       __vfs_write+0xf7/0x760 fs/read_write.c:485
       vfs_write+0x206/0x550 fs/read_write.c:549
       ksys_write+0x12b/0x2a0 fs/read_write.c:599
       do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #1 (&port_lock_key){-.-.}:
       serial8250_console_write+0x79f/0x9c0 drivers/tty/serial/8250/8250_port.c:3251
       call_console_drivers kernel/printk/printk.c:1736 [inline]
       console_unlock+0xb26/0xfe0 kernel/printk/printk.c:2429
       vprintk_emit+0x282/0x6e0 kernel/printk/printk.c:1937
       vprintk_func+0x79/0x17e kernel/printk/printk_safe.c:398
       printk+0xba/0xed kernel/printk/printk.c:2012
       register_console+0x752/0xb50 kernel/printk/printk.c:2745
       univ8250_console_init+0x3a/0x46 drivers/tty/serial/8250/8250_core.c:684
       console_init+0x4cb/0x718 kernel/printk/printk.c:2831
       start_kernel+0x594/0x81c init/main.c:660
       secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243

-> #0 (console_owner){-.-.}:
       console_lock_spinning_enable kernel/printk/printk.c:1599 [inline]
       console_unlock+0x45c/0xfe0 kernel/printk/printk.c:2426
       vprintk_emit+0x282/0x6e0 kernel/printk/printk.c:1937
       vprintk_func+0x79/0x17e kernel/printk/printk_safe.c:398
       printk+0xba/0xed kernel/printk/printk.c:2012
       show_pwq kernel/workqueue.c:4488 [inline]
       show_workqueue_state.cold+0x94a/0x1059 kernel/workqueue.c:4584
       wq_watchdog_timer_fn+0x4d8/0x550 kernel/workqueue.c:5596
       call_timer_fn+0x177/0x700 kernel/time/timer.c:1326
       expire_timers kernel/time/timer.c:1363 [inline]
       __run_timers kernel/time/timer.c:1684 [inline]
       __run_timers kernel/time/timer.c:1652 [inline]
       run_timer_softirq+0xc08/0x1540 kernel/time/timer.c:1699
       __do_softirq+0x26c/0x93c kernel/softirq.c:292
       invoke_softirq kernel/softirq.c:372 [inline]
       irq_exit+0x17b/0x1c0 kernel/softirq.c:412
       exiting_irq arch/x86/include/asm/apic.h:544 [inline]
       smp_apic_timer_interrupt+0x136/0x550 arch/x86/kernel/apic/apic.c:1094
       apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:893
       native_safe_halt+0xe/0x10 arch/x86/include/asm/irqflags.h:60
       arch_safe_halt arch/x86/include/asm/paravirt.h:94 [inline]
       default_idle+0x49/0x320 arch/x86/kernel/process.c:565
       cpuidle_idle_call kernel/sched/idle.c:153 [inline]
       do_idle+0x2ee/0x4b0 kernel/sched/idle.c:263
       cpu_startup_entry+0xc6/0xd0 kernel/sched/idle.c:369
       start_kernel+0x7e4/0x81c init/main.c:737
       secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243

other info that might help us debug this:

Chain exists of:
  console_owner --> &pool->lock/1 --> &(&pool->lock)->rlock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&(&pool->lock)->rlock);
                               lock(&pool->lock/1);
                               lock(&(&pool->lock)->rlock);
  lock(console_owner);

 *** DEADLOCK ***

4 locks held by swapper/0/0:
 #0: 0000000034ec4a0a ((&wq_watchdog_timer)){+.-.}, at: lockdep_copy_map include/linux/lockdep.h:168 [inline]
 #0: 0000000034ec4a0a ((&wq_watchdog_timer)){+.-.}, at: call_timer_fn+0xc9/0x700 kernel/time/timer.c:1316
 #1: 00000000ba384d92 (rcu_read_lock_sched){....}, at: show_workqueue_state+0x0/0x120 kernel/workqueue.c:4453
 #2: 000000004837dceb (&(&pool->lock)->rlock){-.-.}, at: show_workqueue_state.cold+0x7f9/0x1059 kernel/workqueue.c:4582
 #3: 0000000071a979bc (console_lock){+.+.}, at: console_trylock_spinning kernel/printk/printk.c:1661 [inline]
 #3: 0000000071a979bc (console_lock){+.+.}, at: vprintk_emit+0x269/0x6e0 kernel/printk/printk.c:1936

stack backtrace:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.19.109-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x188/0x20d lib/dump_stack.c:118
 print_circular_bug.isra.0.cold+0x1c4/0x282 kernel/locking/lockdep.c:1221
 check_prev_add kernel/locking/lockdep.c:1861 [inline]
 check_prevs_add kernel/locking/lockdep.c:1974 [inline]
 validate_chain kernel/locking/lockdep.c:2415 [inline]
 __lock_acquire+0x2e19/0x49c0 kernel/locking/lockdep.c:3411
 lock_acquire+0x170/0x400 kernel/locking/lockdep.c:3903
 console_lock_spinning_enable kernel/printk/printk.c:1599 [inline]
 console_unlock+0x45c/0xfe0 kernel/printk/printk.c:2426
 vprintk_emit+0x282/0x6e0 kernel/printk/printk.c:1937
 vprintk_func+0x79/0x17e kernel/printk/printk_safe.c:398
 printk+0xba/0xed kernel/printk/printk.c:2012
 show_pwq kernel/workqueue.c:4488 [inline]
 show_workqueue_state.cold+0x94a/0x1059 kernel/workqueue.c:4584
 wq_watchdog_timer_fn+0x4d8/0x550 kernel/workqueue.c:5596
 call_timer_fn+0x177/0x700 kernel/time/timer.c:1326
 expire_timers kernel/time/timer.c:1363 [inline]
 __run_timers kernel/time/timer.c:1684 [inline]
 __run_timers kernel/time/timer.c:1652 [inline]
 run_timer_softirq+0xc08/0x1540 kernel/time/timer.c:1699
 __do_softirq+0x26c/0x93c kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:372 [inline]
 irq_exit+0x17b/0x1c0 kernel/softirq.c:412
 exiting_irq arch/x86/include/asm/apic.h:544 [inline]
 smp_apic_timer_interrupt+0x136/0x550 arch/x86/kernel/apic/apic.c:1094
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:893
 </IRQ>
RIP: 0010:native_safe_halt+0xe/0x10 arch/x86/include/asm/irqflags.h:61
Code: fa eb 82 90 90 90 90 90 90 90 90 90 e9 07 00 00 00 0f 00 2d 04 f1 48 00 f4 c3 66 90 e9 07 00 00 00 0f 00 2d f4 f0 48 00 fb f4 <c3> 90 41 56 41 55 41 54 55 53 e8 43 bc 37 fa e8 3e c7 36 fc 0f 1f
RSP: 0018:ffffffff88a07d40 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13
RAX: 1ffffffff1164ad4 RBX: dffffc0000000000 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: 0000000000000001 RDI: ffffffff88a7a73c
RBP: 0000000000000000 R08: ffffffff88a79ec0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff88b25690
R13: 0000000000000000 R14: 0000000000000000 R15: ffffffff88a79ec0
 arch_safe_halt arch/x86/include/asm/paravirt.h:94 [inline]
 default_idle+0x49/0x320 arch/x86/kernel/process.c:565
 cpuidle_idle_call kernel/sched/idle.c:153 [inline]
 do_idle+0x2ee/0x4b0 kernel/sched/idle.c:263
 cpu_startup_entry+0xc6/0xd0 kernel/sched/idle.c:369
 start_kernel+0x7e4/0x81c init/main.c:737
 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243
workqueue events_power_efficient: flags=0x80
  pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=2/256 refcnt=3
    pending: do_cache_clean, check_lifetime
workqueue rcu_gp: flags=0x8
  pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=1/256 refcnt=2
    in-flight: 19:srcu_invoke_callbacks
workqueue mm_percpu_wq: flags=0x8
  pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=1/256 refcnt=2
    pending: vmstat_update
workqueue dm_bufio_cache: flags=0x8
  pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=1/256 refcnt=2
    pending: work_fn
workqueue krxrpcd: flags=0x0
  pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=1/1 refcnt=2
    pending: rxrpc_peer_keepalive_worker
pool 2: cpus=1 node=0 flags=0x0 nice=0 hung=164s workers=2 idle: 2914