INFO: task hung in tty_open

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 4f68020f Linux 4.14.182
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=116ba526100000
kernel config: https://syzkaller.appspot.com/x/.config?x=c7045c57a90d1ddc
dashboard link: https://syzkaller.appspot.com/bug?extid=e338e41b2fc166625271
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+e338e4...@syzkaller.appspotmail.com

INFO: task syz-executor.3:14134 blocked for more than 140 seconds.
Not tainted 4.14.182-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.3 D28912 14134 4202 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x8a6/0x1d70 kernel/sched/core.c:3384
schedule+0x8d/0x1b0 kernel/sched/core.c:3428
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:3486
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x5f0/0x1430 kernel/locking/mutex.c:893
tty_open_by_driver drivers/tty/tty_io.c:1937 [inline]
tty_open+0x321/0x860 drivers/tty/tty_io.c:2021
chrdev_open+0x1fc/0x540 fs/char_dev.c:423
do_dentry_open+0x44b/0xec0 fs/open.c:777
vfs_open+0x105/0x220 fs/open.c:888
do_last fs/namei.c:3428 [inline]
path_openat+0xb68/0x2aa0 fs/namei.c:3569
do_filp_open+0x18e/0x250 fs/namei.c:3603
do_sys_open+0x292/0x3e0 fs/open.c:1081
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x416821
RSP: 002b:00007fc8814997a0 EFLAGS: 00000293 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 00000000005094c0 RCX: 0000000000416821
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 00007fc8814997d0
RBP: 000000000078bfa0 R08: 0000000000000000 R09: 000000000000000d
R10: 0000000000000064 R11: 0000000000000293 R12: 00000000ffffffff
R13: 0000000000000c1a R14: 00000000004ce670 R15: 00007fc88149a6d4
INFO: task syz-executor.5:14139 blocked for more than 140 seconds.
Not tainted 4.14.182-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.5 D28480 14139 18229 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x8a6/0x1d70 kernel/sched/core.c:3384
schedule+0x8d/0x1b0 kernel/sched/core.c:3428
schedule_timeout+0x86c/0xe50 kernel/time/timer.c:1723
__down_common kernel/locking/semaphore.c:221 [inline]
__down+0x17f/0x280 kernel/locking/semaphore.c:238
down+0x57/0x80 kernel/locking/semaphore.c:62
console_lock+0x24/0x70 kernel/printk/printk.c:2216
con_install+0x46/0x490 drivers/tty/vt/vt.c:2891
tty_driver_install_tty drivers/tty/tty_io.c:1225 [inline]
tty_init_dev drivers/tty/tty_io.c:1338 [inline]
tty_init_dev+0xe1/0x3a0 drivers/tty/tty_io.c:1315
tty_open_by_driver drivers/tty/tty_io.c:1973 [inline]
tty_open+0x5e6/0x860 drivers/tty/tty_io.c:2021
chrdev_open+0x1fc/0x540 fs/char_dev.c:423
do_dentry_open+0x44b/0xec0 fs/open.c:777
vfs_open+0x105/0x220 fs/open.c:888
do_last fs/namei.c:3428 [inline]
path_openat+0xb68/0x2aa0 fs/namei.c:3569
do_filp_open+0x18e/0x250 fs/namei.c:3603
do_sys_open+0x292/0x3e0 fs/open.c:1081
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x416821
RSP: 002b:00007efdf27237a0 EFLAGS: 00000293 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 0000000000509500 RCX: 0000000000416821
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 00007efdf27237d0
RBP: 000000000078bf00 R08: 0000000000000000 R09: 000000000000000e
R10: 0000000000000064 R11: 0000000000000293 R12: 00000000ffffffff
R13: 0000000000000c1b R14: 00000000004ce682 R15: 00007efdf27246d4
INFO: task syz-executor.5:14141 blocked for more than 140 seconds.
Not tainted 4.14.182-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.5 D28288 14141 18229 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x8a6/0x1d70 kernel/sched/core.c:3384
schedule+0x8d/0x1b0 kernel/sched/core.c:3428
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:3486
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x5f0/0x1430 kernel/locking/mutex.c:893
tty_open_by_driver drivers/tty/tty_io.c:1937 [inline]
tty_open+0x321/0x860 drivers/tty/tty_io.c:2021
chrdev_open+0x1fc/0x540 fs/char_dev.c:423
do_dentry_open+0x44b/0xec0 fs/open.c:777
vfs_open+0x105/0x220 fs/open.c:888
do_last fs/namei.c:3428 [inline]
path_openat+0xb68/0x2aa0 fs/namei.c:3569
do_filp_open+0x18e/0x250 fs/namei.c:3603
do_sys_open+0x292/0x3e0 fs/open.c:1081
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x416821
RSP: 002b:00007efdf27027a0 EFLAGS: 00000293 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 0000000000509500 RCX: 0000000000416821
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 00007efdf27027d0
RBP: 000000000078bfa0 R08: 0000000000000000 R09: 000000000000000e
R10: 0000000000000064 R11: 0000000000000293 R12: 00000000ffffffff
R13: 0000000000000c1b R14: 00000000004ce682 R15: 00007efdf27036d4

Showing all locks held in the system:
1 lock held by khungtaskd/1056:
#0: (tasklist_lock){.+.+}, at: [<ffffffff8146c8d0>] debug_show_all_locks+0x7c/0x21a kernel/locking/lockdep.c:4548
1 lock held by in:imklog/5928:
#0: (&f->f_pos_lock){+.+.}, at: [<ffffffff8191ee16>] __fdget_pos+0xa6/0xc0 fs/file.c:769
2 locks held by agetty/6008:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff833be562>] tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:284
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff833b9b44>] n_tty_read+0x1e4/0x16e0 drivers/tty/n_tty.c:2156
1 lock held by syz-executor.3/14134:
#0: (tty_mutex){+.+.}, at: [<ffffffff833ade31>] tty_open_by_driver drivers/tty/tty_io.c:1937 [inline]
#0: (tty_mutex){+.+.}, at: [<ffffffff833ade31>] tty_open+0x321/0x860 drivers/tty/tty_io.c:2021
2 locks held by syz-executor.5/14139:
#0: (tty_mutex){+.+.}, at: [<ffffffff833ade31>] tty_open_by_driver drivers/tty/tty_io.c:1937 [inline]
#0: (tty_mutex){+.+.}, at: [<ffffffff833ade31>] tty_open+0x321/0x860 drivers/tty/tty_io.c:2021
#1: (&tty->legacy_mutex){+.+.}, at: [<ffffffff833c411f>] tty_lock+0x5f/0x70 drivers/tty/tty_mutex.c:19
1 lock held by syz-executor.5/14141:
#0: (tty_mutex){+.+.}, at: [<ffffffff833ade31>] tty_open_by_driver drivers/tty/tty_io.c:1937 [inline]
#0: (tty_mutex){+.+.}, at: [<ffffffff833ade31>] tty_open+0x321/0x860 drivers/tty/tty_io.c:2021

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

NMI backtrace for cpu 1
CPU: 1 PID: 1056 Comm: khungtaskd Not tainted 4.14.182-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+0x5e2/0xb80 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: 14132 Comm: syz-executor.3 Not tainted 4.14.182-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff88801545e3c0 task.stack: ffff88808c268000
RIP: 0010:__writeq arch/x86/include/asm/io.h:100 [inline]
RIP: 0010:bitfill_aligned drivers/video/fbdev/core/cfbfillrect.c:69 [inline]
RIP: 0010:bitfill_aligned+0xe7/0x190 drivers/video/fbdev/core/cfbfillrect.c:35
RSP: 0018:ffff88808c26f108 EFLAGS: 00000246
RAX: 0000000000040000 RBX: ffff8880000a0080 RCX: ffffc90008d17000
RDX: 0000000000040000 RSI: ffffffff831c0be4 RDI: 0000000000000a00
RBP: 0000000000000028 R08: 0000000000000a00 R09: 0000000000000040
R10: ffffed1014bec01b R11: ffff8880a5f600df R12: ffff8880000a0140
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS: 00007fc8814bb700(0000) GS:ffff8880aec00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c009b31ac0 CR3: 000000009ff05000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
cfb_fillrect+0x3d5/0x720 drivers/video/fbdev/core/cfbfillrect.c:327
vga16fb_fillrect+0x61e/0x1880 drivers/video/fbdev/vga16fb.c:951
bit_clear_margins+0x2a4/0x480 drivers/video/fbdev/core/bitblit.c:232
fbcon_clear_margins+0x274/0x300 drivers/video/fbdev/core/fbcon.c:1320
ypan_up_redraw drivers/video/fbdev/core/fbcon.c:1505 [inline]
fbcon_scroll+0xcd6/0x33c0 drivers/video/fbdev/core/fbcon.c:1883
con_scroll+0x294/0x310 drivers/tty/vt/vt.c:327
lf+0x226/0x270 drivers/tty/vt/vt.c:1134
do_con_trol+0x493/0x52e0 drivers/tty/vt/vt.c:1797
do_con_write.part.0+0xc44/0x1a20 drivers/tty/vt/vt.c:2447
do_con_write drivers/tty/vt/vt.c:2218 [inline]
con_write+0x33/0xc0 drivers/tty/vt/vt.c:2798
do_output_char+0x4f5/0x750 drivers/tty/n_tty.c:447
process_output drivers/tty/n_tty.c:514 [inline]
n_tty_write+0x409/0xe20 drivers/tty/n_tty.c:2345
do_tty_write drivers/tty/tty_io.c:959 [inline]
tty_write+0x3f1/0x6e0 drivers/tty/tty_io.c:1043
__vfs_write+0xe4/0x630 fs/read_write.c:480
__kernel_write+0xf5/0x330 fs/read_write.c:501
write_pipe_buf+0x143/0x1b0 fs/splice.c:797
splice_from_pipe_feed fs/splice.c:502 [inline]
__splice_from_pipe+0x332/0x740 fs/splice.c:626
splice_from_pipe+0xc6/0x120 fs/splice.c:661
default_file_splice_write+0x37/0x80 fs/splice.c:809
do_splice_from fs/splice.c:851 [inline]
direct_splice_actor+0x115/0x160 fs/splice.c:1018
splice_direct_to_actor+0x27e/0x730 fs/splice.c:973
do_splice_direct+0x164/0x210 fs/splice.c:1061
do_sendfile+0x469/0xaf0 fs/read_write.c:1441
SYSC_sendfile64 fs/read_write.c:1502 [inline]
SyS_sendfile64+0xff/0x110 fs/read_write.c:1488
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x45ca29
RSP: 002b:00007fc8814bac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00000000004fc540 RCX: 000000000045ca29
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000003
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0800000080004103 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000008dc R14: 00000000004cba16 R15: 00007fc8814bb6d4
Code: 44 8d 60 f8 41 c1 ec 03 49 83 c4 01 49 c1 e4 06 49 01 dc e8 2c 96 3e fe 4c 89 3b 4c 89 7b 08 4c 89 7b 10 4c 89 7b 18 4c 89 7b 20 <4c> 89 7b 28 48 8d 43 38 4c 89 7b 30 48 83 c3 40 4c 89 38 49 39


---
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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.