syzbot

INFO: task syz-executor046:8416 blocked for more than 140 seconds.
      Not tainted 4.14.209-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor046 D28912  8416   7986 0x00000004
Call Trace:
 context_switch kernel/sched/core.c:2808 [inline]
 __schedule+0x88b/0x1de0 kernel/sched/core.c:3384
 schedule+0x8d/0x1b0 kernel/sched/core.c:3428
 schedule_timeout+0x80a/0xe90 kernel/time/timer.c:1724
 __down_common kernel/locking/semaphore.c:221 [inline]
 __down+0x16d/0x260 kernel/locking/semaphore.c:238
 down+0x57/0x80 kernel/locking/semaphore.c:62
 console_lock+0x24/0x70 kernel/printk/printk.c:2219
 do_fb_ioctl+0x2e7/0xa70 drivers/video/fbdev/core/fbmem.c:1121
 fb_ioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1242
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x75a/0xff0 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x445189
RSP: 002b:00007ffcec01b8b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000020000080 RCX: 0000000000445189
RDX: 0000000020000000 RSI: 0000000000004601 RDI: 0000000000000003
RBP: 00000000000bed59 R08: 00000000004002e0 R09: 00000000004002e0
R10: 0000000000000004 R11: 0000000000000246 R12: 0000000000402350
R13: 00000000004023e0 R14: 0000000000000000 R15: 0000000000000000

Showing all locks held in the system:
1 lock held by khungtaskd/1532:
 #0:  (tasklist_lock){.+.+}, at: [<ffffffff81430cb4>] debug_show_all_locks+0x7c/0x21a kernel/locking/lockdep.c:4548
1 lock held by in:imklog/7651:
 #0:  (&f->f_pos_lock){+.+.}, at: [<ffffffff818f8acb>] __fdget_pos+0x1fb/0x2b0 fs/file.c:769
2 locks held by agetty/7701:
 #0:  (&tty->ldisc_sem){++++}, at: [<ffffffff835e40d2>] tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:284
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff835d9423>] n_tty_read+0x1e3/0x1680 drivers/tty/n_tty.c:2156

=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 1532 Comm: khungtaskd Not tainted 4.14.209-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x1b2/0x283 lib/dump_stack.c:58
 nmi_cpu_backtrace.cold+0x57/0x93 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x13a/0x17f lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:140 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:195 [inline]
 watchdog+0x5b9/0xb40 kernel/hung_task.c:274
 kthread+0x30d/0x420 kernel/kthread.c:232
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 22 Comm: kworker/u4:1 Not tainted 4.14.209-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_unbound flush_to_ldisc
task: ffff8880b55f85c0 task.stack: ffff8880b5600000
RIP: 0010:__sanitizer_cov_trace_pc+0x23/0x50 kernel/kcov.c:68
RSP: 0018:ffff8880b56075f8 EFLAGS: 00000246
RAX: ffff8880b55f85c0 RBX: ffff8880000a0035 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffff8880b5607690 RDI: ffff8880b56076a0
RBP: 0000000000000050 R08: 0000000000000010 R09: 0000000000000280
R10: ffffffff8c8ad014 R11: 0000000000000000 R12: 00000000aa32f28e
R13: ffffffffffffffb0 R14: ffff8880000a0050 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8880ba400000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000006cf090 CR3: 00000000b3a82000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 writeb arch/x86/include/asm/io.h:65 [inline]
 vga16fb_fillrect+0x910/0x1820 drivers/video/fbdev/vga16fb.c:923
 bit_clear+0x32a/0x450 drivers/video/fbdev/core/bitblit.c:74
 fbcon_clear+0x558/0x650 drivers/video/fbdev/core/fbcon.c:1236
 fbcon_scroll+0x3c1/0x31e0 drivers/video/fbdev/core/fbcon.c:1734
 con_scroll+0x2c5/0x360 drivers/tty/vt/vt.c:327
 lf+0x226/0x270 drivers/tty/vt/vt.c:1141
 do_con_write+0xf9b/0x19b0 drivers/tty/vt/vt.c:2414
 con_put_char+0x78/0xa0 drivers/tty/vt/vt.c:2815
 tty_put_char+0xa3/0x120 drivers/tty/tty_io.c:2879
 do_output_char+0x126/0x750 drivers/tty/n_tty.c:488
 __process_echoes+0x313/0x8c0 drivers/tty/n_tty.c:739
 flush_echoes drivers/tty/n_tty.c:829 [inline]
 __receive_buf drivers/tty/n_tty.c:1648 [inline]
 n_tty_receive_buf_common+0x9a3/0x25a0 drivers/tty/n_tty.c:1742
 tty_ldisc_receive_buf+0x9e/0x170 drivers/tty/tty_buffer.c:455
 tty_port_default_receive_buf+0x6e/0xa0 drivers/tty/tty_port.c:37
 receive_buf drivers/tty/tty_buffer.c:475 [inline]
 flush_to_ldisc+0x1dd/0x3f0 drivers/tty/tty_buffer.c:527
 process_one_work+0x793/0x14a0 kernel/workqueue.c:2116
 worker_thread+0x5cc/0xff0 kernel/workqueue.c:2250
 kthread+0x30d/0x420 kernel/kthread.c:232
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404
Code: 00 00 e9 c6 ed ff ff 90 65 48 8b 04 25 80 df 01 00 48 85 c0 74 1a 65 8b 15 bb 9f aa 7e 81 e2 00 01 1f 00 75 0b 8b 90 58 13 00 00 <83> fa 01 74 01 c3 48 8b 34 24 48 8b 88 60 13 00 00 8b 80 5c 13