Re: [syzbot] [trace?] [bpf?] possible deadlock in __mod_timer (4)

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On Thu 2024-09-26 00:53:21, Steven Rostedt wrote:
> On Sat, 21 Sep 2024 23:39:17 -0700
> syzbot <syzbot+83a876aef81c9a485ae8@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> 
> > Hello,
> > 
> > syzbot found the following issue on:
> > 
> > HEAD commit:    a940d9a43e62 Merge tag 'soc-arm-6.12' of git://git.kernel...
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=12d1c69f980000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=44d46e514184cd24
> > dashboard link: https://syzkaller.appspot.com/bug?extid=83a876aef81c9a485ae8
> > compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11597677980000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13cd7500580000
> > 
> > Downloadable assets:
> > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7bc7510fe41f/non_bootable_disk-a940d9a4.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/e9929bfe422c/vmlinux-a940d9a4.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/a6c74ee261ed/bzImage-a940d9a4.xz
> > 
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+83a876aef81c9a485ae8@xxxxxxxxxxxxxxxxxxxxxxxxx
> > 
> > FAULT_INJECTION: forcing a failure.
> > name fail_usercopy, interval 1, probability 0, space 0, times 1
> > ======================================================
> > WARNING: possible circular locking dependency detected
> > 6.11.0-syzkaller-03917-ga940d9a43e62 #0 Not tainted
> > ------------------------------------------------------
> > syz-executor291/5332 is trying to acquire lock:
> > ffffffff8dda88d8 ((console_sem).lock){-...}-{2:2}, at: down_trylock+0x12/0x70 kernel/locking/semaphore.c:139
> 
> I'm assuming that lockdep splats like this will no longer be an issue come 6.12?

I am afraid that it still would happen in 6.12. :-(

The legacy loop (console_trylock()/unlock()) will still be called
there when there is a boot or a legacy console registered.

I actually guess that all console will be legacy in 6.12 because
the conversion of the uart 8250 console driver still need some love,
see the last version at
https://lore.kernel.org/r/20240913140538.221708-1-john.ogness@xxxxxxxxxxxxx

The only exception will be CONFIG_RT mode which would offload even
the legacy loop to a dedicated kthread.

Best Regards,
Petr

> > 
> > but task is already holding lock:
> > ffff88806a92a858 (&base->lock){-.-.}-{2:2}, at: __mod_timer+0x6c1/0xdc0 kernel/time/timer.c:1164
> > 
> > which lock already depends on the new lock.
> > 
> > 
> > the existing dependency chain (in reverse order) is:
> > 
> > -> #3 (&base->lock){-.-.}-{2:2}:  
> >        __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> >        _raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:162
> >        lock_timer_base+0x5d/0x220 kernel/time/timer.c:1051
> >        __mod_timer+0x426/0xdc0 kernel/time/timer.c:1132
> >        add_timer_global+0x8a/0xc0 kernel/time/timer.c:1330
> >        __queue_delayed_work+0x1ba/0x2e0 kernel/workqueue.c:2525
> >        queue_delayed_work_on+0x12a/0x150 kernel/workqueue.c:2554
> >        psi_task_change+0x1b4/0x2e0 kernel/sched/psi.c:913
> >        psi_enqueue kernel/sched/stats.h:143 [inline]
> >        enqueue_task+0x1a5/0x350 kernel/sched/core.c:1975
> >        activate_task kernel/sched/core.c:2009 [inline]
> >        wake_up_new_task+0x5ba/0xd30 kernel/sched/core.c:4689
> >        kernel_clone+0x236/0x960 kernel/fork.c:2812
> >        user_mode_thread+0xb4/0xf0 kernel/fork.c:2859
> >        rest_init+0x23/0x2b0 init/main.c:712
> >        start_kernel+0x3e4/0x4d0 init/main.c:1105
> >        x86_64_start_reservations+0x18/0x30 arch/x86/kernel/head64.c:507
> >        x86_64_start_kernel+0xb2/0xc0 arch/x86/kernel/head64.c:488
> >        common_startup_64+0x13e/0x148
> > 
> > -> #2 (&rq->__lock){-.-.}-{2:2}:  
> >        _raw_spin_lock_nested+0x31/0x40 kernel/locking/spinlock.c:378
> >        raw_spin_rq_lock_nested+0x29/0x130 kernel/sched/core.c:560
> >        raw_spin_rq_lock kernel/sched/sched.h:1415 [inline]
> >        rq_lock kernel/sched/sched.h:1714 [inline]
> >        task_fork_fair+0x73/0x250 kernel/sched/fair.c:12710
> >        sched_cgroup_fork+0x3cf/0x510 kernel/sched/core.c:4633
> >        copy_process+0x439b/0x8dd0 kernel/fork.c:2483
> >        kernel_clone+0xfd/0x960 kernel/fork.c:2781
> >        user_mode_thread+0xb4/0xf0 kernel/fork.c:2859
> >        rest_init+0x23/0x2b0 init/main.c:712
> >        start_kernel+0x3e4/0x4d0 init/main.c:1105
> >        x86_64_start_reservations+0x18/0x30 arch/x86/kernel/head64.c:507
> >        x86_64_start_kernel+0xb2/0xc0 arch/x86/kernel/head64.c:488
> >        common_startup_64+0x13e/0x148
> > 
> > -> #1 (&p->pi_lock){-.-.}-{2:2}:  
> >        __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> >        _raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:162
> >        class_raw_spinlock_irqsave_constructor include/linux/spinlock.h:551 [inline]
> >        try_to_wake_up+0x9a/0x13e0 kernel/sched/core.c:4051
> >        up+0x79/0xb0 kernel/locking/semaphore.c:191
> >        __up_console_sem+0x85/0xe0 kernel/printk/printk.c:343
> >        __console_unlock kernel/printk/printk.c:2844 [inline]
> >        __console_flush_and_unlock kernel/printk/printk.c:3241 [inline]
> >        console_unlock+0x1dc/0x210 kernel/printk/printk.c:3279
> >        vga_remove_vgacon drivers/pci/vgaarb.c:186 [inline]
> >        vga_remove_vgacon+0x90/0xd0 drivers/pci/vgaarb.c:167
> >        __aperture_remove_legacy_vga_devices drivers/video/aperture.c:331 [inline]
> >        aperture_remove_conflicting_pci_devices+0x16a/0x1e0 drivers/video/aperture.c:369
> >        virtio_gpu_pci_quirk drivers/gpu/drm/virtio/virtgpu_drv.c:61 [inline]
> >        virtio_gpu_probe+0x408/0x4e0 drivers/gpu/drm/virtio/virtgpu_drv.c:92
> >        virtio_dev_probe+0x586/0x8a0 drivers/virtio/virtio.c:341
> >        call_driver_probe drivers/base/dd.c:578 [inline]
> >        really_probe+0x23e/0xa90 drivers/base/dd.c:657
> >        __driver_probe_device+0x1de/0x440 drivers/base/dd.c:799
> >        driver_probe_device+0x4c/0x1b0 drivers/base/dd.c:829
> >        __driver_attach+0x283/0x580 drivers/base/dd.c:1215
> >        bus_for_each_dev+0x13c/0x1d0 drivers/base/bus.c:368
> >        bus_add_driver+0x2e9/0x690 drivers/base/bus.c:673
> >        driver_register+0x15c/0x4b0 drivers/base/driver.c:246
> >        do_one_initcall+0x128/0x700 init/main.c:1269
> >        do_initcall_level init/main.c:1331 [inline]
> >        do_initcalls init/main.c:1347 [inline]
> >        do_basic_setup init/main.c:1366 [inline]
> >        kernel_init_freeable+0x69d/0xca0 init/main.c:1580
> >        kernel_init+0x1c/0x2b0 init/main.c:1469
> >        ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
> >        ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> > 
> > -> #0 ((console_sem).lock){-...}-{2:2}:  
> >        check_prev_add kernel/locking/lockdep.c:3158 [inline]
> >        check_prevs_add kernel/locking/lockdep.c:3277 [inline]
> >        validate_chain kernel/locking/lockdep.c:3901 [inline]
> >        __lock_acquire+0x250b/0x3ce0 kernel/locking/lockdep.c:5199
> >        lock_acquire kernel/locking/lockdep.c:5822 [inline]
> >        lock_acquire+0x1b1/0x560 kernel/locking/lockdep.c:5787
> >        __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> >        _raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:162
> >        down_trylock+0x12/0x70 kernel/locking/semaphore.c:139
> >        __down_trylock_console_sem+0x40/0x140 kernel/printk/printk.c:326
> >        console_trylock kernel/printk/printk.c:2827 [inline]
> >        console_trylock_spinning kernel/printk/printk.c:1990 [inline]
> >        vprintk_emit+0x3ec/0x6f0 kernel/printk/printk.c:2406
> >        vprintk+0x7f/0xa0 kernel/printk/printk_safe.c:68
> >        _printk+0xc8/0x100 kernel/printk/printk.c:2432
> >        fail_dump lib/fault-inject.c:45 [inline]
> >        should_fail_ex+0x46c/0x5b0 lib/fault-inject.c:153
> >        strncpy_from_user+0x38/0x320 lib/strncpy_from_user.c:118
> >        strncpy_from_user_nofault+0x7f/0x180 mm/maccess.c:186
> >        bpf_probe_read_user_str_common kernel/trace/bpf_trace.c:216 [inline]
> >        ____bpf_probe_read_compat_str kernel/trace/bpf_trace.c:311 [inline]
> >        bpf_probe_read_compat_str+0xf1/0x170 kernel/trace/bpf_trace.c:307
> >        bpf_prog_d0e9ac47b081aec3+0x48/0x4a
> >        bpf_dispatcher_nop_func include/linux/bpf.h:1243 [inline]
> >        __bpf_prog_run include/linux/filter.h:691 [inline]
> >        bpf_prog_run include/linux/filter.h:698 [inline]
> >        __bpf_trace_run kernel/trace/bpf_trace.c:2406 [inline]
> >        bpf_trace_run2+0x231/0x590 kernel/trace/bpf_trace.c:2447
> >        __bpf_trace_timer_start+0xc7/0x100 include/trace/events/timer.h:52
> >        trace_timer_start include/trace/events/timer.h:52 [inline]
> >        enqueue_timer+0x2b4/0x550 kernel/time/timer.c:663
> >        internal_add_timer kernel/time/timer.c:688 [inline]
> >        __mod_timer+0x8d7/0xdc0 kernel/time/timer.c:1183
> >        add_timer_global+0x8a/0xc0 kernel/time/timer.c:1330
> >        __queue_delayed_work+0x1ba/0x2e0 kernel/workqueue.c:2525
> >        queue_delayed_work_on+0x12a/0x150 kernel/workqueue.c:2554
> >        queue_delayed_work include/linux/workqueue.h:636 [inline]
> >        fbcon_add_cursor_work drivers/video/fbdev/core/fbcon.c:392 [inline]
> >        fbcon_cursor+0x4a0/0x520 drivers/video/fbdev/core/fbcon.c:1316
> >        hide_cursor+0x84/0x220 drivers/tty/vt/vt.c:846
> >        do_con_write+0x21e6/0x7bb0 drivers/tty/vt/vt.c:3068
> >        con_write+0x23/0xb0 drivers/tty/vt/vt.c:3434
> >        process_output_block drivers/tty/n_tty.c:574 [inline]
> >        n_tty_write+0x419/0x1140 drivers/tty/n_tty.c:2389
> >        iterate_tty_write drivers/tty/tty_io.c:1021 [inline]
> >        file_tty_write.constprop.0+0x506/0x9a0 drivers/tty/tty_io.c:1096
> >        new_sync_write fs/read_write.c:590 [inline]
> >        vfs_write+0x6b5/0x1140 fs/read_write.c:683
> >        ksys_write+0x12f/0x260 fs/read_write.c:736
> >        do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >        do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
> >        entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > 
> > other info that might help us debug this:
> > 
> > Chain exists of:
> >   (console_sem).lock --> &rq->__lock --> &base->lock
> > 
> >  Possible unsafe locking scenario:
> > 
> >        CPU0                    CPU1
> >        ----                    ----
> >   lock(&base->lock);
> >                                lock(&rq->__lock);
> >                                lock(&base->lock);
> >   lock((console_sem).lock);
> > 
> >  *** DEADLOCK ***
> > 
> > 7 locks held by syz-executor291/5332:
> >  #0: ffff8880353610a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x24/0x80 drivers/tty/tty_ldisc.c:243
> >  #1: ffff888035361130 (&tty->atomic_write_lock){+.+.}-{3:3}, at: tty_write_lock drivers/tty/tty_io.c:954 [inline]
> >  #1: ffff888035361130 (&tty->atomic_write_lock){+.+.}-{3:3}, at: iterate_tty_write drivers/tty/tty_io.c:973 [inline]
> >  #1: ffff888035361130 (&tty->atomic_write_lock){+.+.}-{3:3}, at: file_tty_write.constprop.0+0x281/0x9a0 drivers/tty/tty_io.c:1096
> >  #2: ffff8880353612e8 (&tty->termios_rwsem){++++}-{3:3}, at: n_tty_write+0x1bd/0x1140 drivers/tty/n_tty.c:2372
> >  #3: ffffc9000324e380 (&ldata->output_lock){+.+.}-{3:3}, at: process_output_block drivers/tty/n_tty.c:529 [inline]
> >  #3: ffffc9000324e380 (&ldata->output_lock){+.+.}-{3:3}, at: n_tty_write+0x533/0x1140 drivers/tty/n_tty.c:2389
> >  #4: ffffffff8dda8460 (console_lock){+.+.}-{0:0}, at: do_con_write+0x154/0x7bb0 drivers/tty/vt/vt.c:3056
> >  #5: ffff88806a92a858 (&base->lock){-.-.}-{2:2}, at: __mod_timer+0x6c1/0xdc0 kernel/time/timer.c:1164
> >  #6: ffffffff8ddbaea0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:326 [inline]
> >  #6: ffffffff8ddbaea0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
> >  #6: ffffffff8ddbaea0 (rcu_read_lock){....}-{1:2}, at: __bpf_trace_run kernel/trace/bpf_trace.c:2405 [inline]
> >  #6: ffffffff8ddbaea0 (rcu_read_lock){....}-{1:2}, at: bpf_trace_run2+0x1c2/0x590 kernel/trace/bpf_trace.c:2447
> > 
> > stack backtrace:
> > CPU: 3 UID: 0 PID: 5332 Comm: syz-executor291 Not tainted 6.11.0-syzkaller-03917-ga940d9a43e62 #0
> > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> > Call Trace:
> >  <TASK>
> >  __dump_stack lib/dump_stack.c:93 [inline]
> >  dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:119
> >  print_circular_bug+0x419/0x5d0 kernel/locking/lockdep.c:2074
> >  check_noncircular+0x31a/0x400 kernel/locking/lockdep.c:2203
> >  check_prev_add kernel/locking/lockdep.c:3158 [inline]
> >  check_prevs_add kernel/locking/lockdep.c:3277 [inline]
> >  validate_chain kernel/locking/lockdep.c:3901 [inline]
> >  __lock_acquire+0x250b/0x3ce0 kernel/locking/lockdep.c:5199
> >  lock_acquire kernel/locking/lockdep.c:5822 [inline]
> >  lock_acquire+0x1b1/0x560 kernel/locking/lockdep.c:5787
> >  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> >  _raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:162
> >  down_trylock+0x12/0x70 kernel/locking/semaphore.c:139
> >  __down_trylock_console_sem+0x40/0x140 kernel/printk/printk.c:326
> >  console_trylock kernel/printk/printk.c:2827 [inline]
> >  console_trylock_spinning kernel/printk/printk.c:1990 [inline]
> >  vprintk_emit+0x3ec/0x6f0 kernel/printk/printk.c:2406
> >  vprintk+0x7f/0xa0 kernel/printk/printk_safe.c:68
> >  _printk+0xc8/0x100 kernel/printk/printk.c:2432
> >  fail_dump lib/fault-inject.c:45 [inline]
> >  should_fail_ex+0x46c/0x5b0 lib/fault-inject.c:153
> >  strncpy_from_user+0x38/0x320 lib/strncpy_from_user.c:118
> >  strncpy_from_user_nofault+0x7f/0x180 mm/maccess.c:186
> >  bpf_probe_read_user_str_common kernel/trace/bpf_trace.c:216 [inline]
> >  ____bpf_probe_read_compat_str kernel/trace/bpf_trace.c:311 [inline]
> >  bpf_probe_read_compat_str+0xf1/0x170 kernel/trace/bpf_trace.c:307
> >  bpf_prog_d0e9ac47b081aec3+0x48/0x4a
> >  bpf_dispatcher_nop_func include/linux/bpf.h:1243 [inline]
> >  __bpf_prog_run include/linux/filter.h:691 [inline]
> >  bpf_prog_run include/linux/filter.h:698 [inline]
> >  __bpf_trace_run kernel/trace/bpf_trace.c:2406 [inline]
> >  bpf_trace_run2+0x231/0x590 kernel/trace/bpf_trace.c:2447
> >  __bpf_trace_timer_start+0xc7/0x100 include/trace/events/timer.h:52
> >  trace_timer_start include/trace/events/timer.h:52 [inline]
> >  enqueue_timer+0x2b4/0x550 kernel/time/timer.c:663
> >  internal_add_timer kernel/time/timer.c:688 [inline]
> >  __mod_timer+0x8d7/0xdc0 kernel/time/timer.c:1183
> >  add_timer_global+0x8a/0xc0 kernel/time/timer.c:1330
> >  __queue_delayed_work+0x1ba/0x2e0 kernel/workqueue.c:2525
> >  queue_delayed_work_on+0x12a/0x150 kernel/workqueue.c:2554
> >  queue_delayed_work include/linux/workqueue.h:636 [inline]
> >  fbcon_add_cursor_work drivers/video/fbdev/core/fbcon.c:392 [inline]
> >  fbcon_cursor+0x4a0/0x520 drivers/video/fbdev/core/fbcon.c:1316
> >  hide_cursor+0x84/0x220 drivers/tty/vt/vt.c:846
> >  do_con_write+0x21e6/0x7bb0 drivers/tty/vt/vt.c:3068
> >  con_write+0x23/0xb0 drivers/tty/vt/vt.c:3434
> >  process_output_block drivers/tty/n_tty.c:574 [inline]
> >  n_tty_write+0x419/0x1140 drivers/tty/n_tty.c:2389
> >  iterate_tty_write drivers/tty/tty_io.c:1021 [inline]
> >  file_tty_write.constprop.0+0x506/0x9a0 drivers/tty/tty_io.c:1096
> >  new_sync_write fs/read_write.c:590 [inline]
> >  vfs_write+0x6b5/0x1140 fs/read_write.c:683
> >  ksys_write+0x12f/0x260 fs/read_write.c:736
> >  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >  do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
> >  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > RIP: 0033:0x7f36b5809869
> > Code: 48 83 c4 28 c3 e8 17 1a 00 00 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> > RSP: 002b:00007ffeb8b42888 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> > RAX: ffffffffffffffda RBX: 00007ffeb8b42890 RCX: 00007f36b5809869
> > RDX: 0000000000001006 RSI: 0000000020001040 RDI: 0000000000000006
> > RBP: 0000000000000001 R08: 00007ffeb8b42627 R09: 00007f36b5870033
> > R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000
> > R13: 00007ffeb8b42a68 R14: 0000000000000001 R15: 0000000000000001
> >  </TASK>
> > CPU: 3 UID: 0 PID: 5332 Comm: syz-executor291 Not tainted 6.11.0-syzkaller-03917-ga940d9a43e62 #0
> > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> > Call Trace:
> >  <TASK>
> >  __dump_stack lib/dump_stack.c:93 [inline]
> >  dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:119
> >  fail_dump lib/fault-inject.c:52 [inline]
> >  should_fail_ex+0x497/0x5b0 lib/fault-inject.c:153
> >  strncpy_from_user+0x38/0x320 lib/strncpy_from_user.c:118
> >  strncpy_from_user_nofault+0x7f/0x180 mm/maccess.c:186
> >  bpf_probe_read_user_str_common kernel/trace/bpf_trace.c:216 [inline]
> >  ____bpf_probe_read_compat_str kernel/trace/bpf_trace.c:311 [inline]
> >  bpf_probe_read_compat_str+0xf1/0x170 kernel/trace/bpf_trace.c:307
> >  bpf_prog_d0e9ac47b081aec3+0x48/0x4a
> >  bpf_dispatcher_nop_func include/linux/bpf.h:1243 [inline]
> >  __bpf_prog_run include/linux/filter.h:691 [inline]
> >  bpf_prog_run include/linux/filter.h:698 [inline]
> >  __bpf_trace_run kernel/trace/bpf_trace.c:2406 [inline]
> >  bpf_trace_run2+0x231/0x590 kernel/trace/bpf_trace.c:2447
> >  __bpf_trace_timer_start+0xc7/0x100 include/trace/events/timer.h:52
> >  trace_timer_start include/trace/events/timer.h:52 [inline]
> >  enqueue_timer+0x2b4/0x550 kernel/time/timer.c:663
> >  internal_add_timer kernel/time/timer.c:688 [inline]
> >  __mod_timer+0x8d7/0xdc0 kernel/time/timer.c:1183
> >  add_timer_global+0x8a/0xc0 kernel/time/timer.c:1330
> >  __queue_delayed_work+0x1ba/0x2e0 kernel/workqueue.c:2525
> >  queue_delayed_work_on+0x12a/0x150 kernel/workqueue.c:2554
> >  queue_delayed_work include/linux/workqueue.h:636 [inline]
> >  fbcon_add_cursor_work drivers/video/fbdev/core/fbcon.c:392 [inline]
> >  fbcon_cursor+0x4a0/0x520 drivers/video/fbdev/core/fbcon.c:1316
> >  hide_cursor+0x84/0x220 drivers/tty/vt/vt.c:846
> >  do_con_write+0x21e6/0x7bb0 drivers/tty/vt/vt.c:3068
> >  con_write+0x23/0xb0 drivers/tty/vt/vt.c:3434
> >  process_output_block drivers/tty/n_tty.c:574 [inline]
> >  n_tty_write+0x419/0x1140 drivers/tty/n_tty.c:2389
> >  iterate_tty_write drivers/tty/tty_io.c:1021 [inline]
> >  file_tty_write.constprop.0+0x506/0x9a0 drivers/tty/tty_io.c:1096
> >  new_sync_write fs/read_write.c:590 [inline]
> >  vfs_write+0x6b5/0x1140 fs/read_write.c:683
> >  ksys_write+0x12f/0x260 fs/read_write.c:736
> >  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >  do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
> >  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > RIP: 0033:0x7f36b5809869
> > Code: 48 83 c4 28 c3 e8 17 1a 00 00 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> > RSP: 002b:00007ffeb8b42888 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> > RAX: ffffffffffffffda RBX: 00007ffeb8b42890 RCX: 00007f36b5809869
> > RDX: 0000000000001006 RSI: 0000000020001040 RDI: 0000000000000006
> > RBP: 0000000000000001 R08: 00007ffeb8b42627 R09: 00007f36b5870033
> > R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000
> > R13: 00007ffeb8b42a68 R14: 0000000000000001 R15: 0000000000000001
> >  </TASK>
> > 
> > 
> > ---
> > This report is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.
> > 
> > syzbot will keep track of this issue. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> > 
> > If the report is already addressed, let syzbot know by replying with:
> > #syz fix: exact-commit-title
> > 
> > If you want syzbot to run the reproducer, reply with:
> > #syz test: git://repo/address.git branch-or-commit-hash
> > If you attach or paste a git patch, syzbot will apply it before testing.
> > 
> > If you want to overwrite report's subsystems, reply with:
> > #syz set subsystems: new-subsystem
> > (See the list of subsystem names on the web dashboard)
> > 
> > If the report is a duplicate of another one, reply with:
> > #syz dup: exact-subject-of-another-report
> > 
> > If you want to undo deduplication, reply with:
> > #syz undup




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