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SubjectINFO: task hung in tty_ldisc_hangup

syzbot found the following crash on:

HEAD commit: 7ada90eb Merge tag 'drm-next-2019-12-06' of git://anongit...
git tree: upstream
console output:
kernel config:
dashboard link:
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:
C reproducer:

Bisection is inconclusive: the bug happens on the oldest tested release.

bisection log:
console output:

IMPORTANT: if you fix the bug, please add the following tag to the commit:

INFO: task login:10239 blocked for more than 143 seconds.
Not tainted 5.4.0-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
login D27648 10239 1 0x80000002
Call Trace:
context_switch kernel/sched/core.c:3385 [inline]
__schedule+0x934/0x1f90 kernel/sched/core.c:4081
schedule+0xdc/0x2b0 kernel/sched/core.c:4155
schedule_timeout+0x717/0xc50 kernel/time/timer.c:1871
down_write_failed drivers/tty/tty_ldsem.c:262 [inline]
__ldsem_down_write_nested+0x3b2/0x8f0 drivers/tty/tty_ldsem.c:324
ldsem_down_write+0x33/0x40 drivers/tty/tty_ldsem.c:366
__tty_ldisc_lock drivers/tty/tty_ldisc.c:315 [inline]
tty_ldisc_lock+0x66/0xb0 drivers/tty/tty_ldisc.c:339
tty_ldisc_hangup+0x1c6/0x640 drivers/tty/tty_ldisc.c:745
__tty_hangup.part.0+0x2fb/0x750 drivers/tty/tty_io.c:625
__tty_hangup drivers/tty/tty_io.c:575 [inline]
tty_vhangup_session+0x25/0x30 drivers/tty/tty_io.c:735
disassociate_ctty.part.0+0xb4/0x740 drivers/tty/tty_jobctrl.c:267
disassociate_ctty+0x81/0xa0 drivers/tty/tty_jobctrl.c:261
do_exit+0x1b42/0x2ef0 kernel/exit.c:795
do_group_exit+0x135/0x360 kernel/exit.c:895
__do_sys_exit_group kernel/exit.c:906 [inline]
__se_sys_exit_group kernel/exit.c:904 [inline]
__x64_sys_exit_group+0x44/0x50 kernel/exit.c:904
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
RIP: 0033:0x7f0f83c781e8
Code: Bad RIP value.
RSP: 002b:00007ffd44a828e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f0f83c781e8
RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
RBP: 00007f0f83f4d840 R08: 00000000000000e7 R09: ffffffffffffffa8
R10: 00007f0f83f53740 R11: 0000000000000246 R12: 00007f0f83f4d840
R13: 0000000000000001 R14: 0000000000000001 R15: 000000000060b798

Showing all locks held in the system:
1 lock held by khungtaskd/1104:
#0: ffffffff899a4280 (rcu_read_lock){....}, at:
debug_show_all_locks+0x5f/0x279 kernel/locking/lockdep.c:5334
1 lock held by rsyslogd/9591:
#0: ffff888098116b60 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0xee/0x110
2 locks held by getty/9714:
#0: ffff88808ec58090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc900018e32e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by getty/9715:
#0: ffff8880a7428090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc900019632e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by getty/9716:
#0: ffff8880a8e92090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc900019032e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by getty/9717:
#0: ffff888093f73090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc900019532e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by getty/9718:
#0: ffff888098ddf090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc900019432e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by getty/9719:
#0: ffff8880a72d4090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc900018a32e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by login/10239:
#0: ffff88809b2d2198 (&tty->legacy_mutex){+.+.}, at: tty_lock+0xc7/0x130
#1: ffff88809b2d2090 (&tty->ldisc_sem){++++}, at:
ldsem_down_write+0x33/0x40 drivers/tty/tty_ldsem.c:366
2 locks held by syz-executor540/10274:


NMI backtrace for cpu 1
CPU: 1 PID: 1104 Comm: khungtaskd Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x197/0x210 lib/dump_stack.c:118
nmi_cpu_backtrace.cold+0x70/0xb2 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x23b/0x28b lib/nmi_backtrace.c:62
arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:205 [inline]
watchdog+0xb11/0x10c0 kernel/hung_task.c:289
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 10274 Comm: syz-executor540 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:preempt_count_add+0x22/0x160 kernel/sched/core.c:3779
Code: 0f 1f 84 00 00 00 00 00 48 c7 c0 e0 24 63 8b 55 48 ba 00 00 00 00 00
fc ff df 48 89 c1 48 89 e5 41 54 83 e0 07 48 c1 e9 03 53 <83> c0 03 89 fb
0f b6 14 11 38 d0 7c 08 84 d2 0f 85 00 01 00 00 8b
RSP: 0018:ffffc90003247628 EFLAGS: 00000806
RAX: 0000000000000000 RBX: ffffc900032476a8 RCX: 1ffffffff16c649c
RDX: dffffc0000000000 RSI: 0000000000000004 RDI: 0000000000000001
RBP: ffffc90003247638 R08: 1ffff11015d07044 R09: ffffed1015d07045
R10: ffffed1015d07044 R11: ffff8880ae838223 R12: ffff8880ae837400
R13: ffffffff899c3620 R14: ffff8880906b4180 R15: 000000000000106e
FS: 0000000001203880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffff600400 CR3: 0000000097677000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
rcu_lockdep_current_cpu_online kernel/rcu/tree.c:969 [inline]
rcu_lockdep_current_cpu_online+0x34/0x130 kernel/rcu/tree.c:961
rcu_read_lock_held_common kernel/rcu/update.c:109 [inline]
rcu_read_lock_held_common+0xbd/0x130 kernel/rcu/update.c:99
rcu_read_lock_held+0x5b/0xb0 kernel/rcu/update.c:281
task_css_set include/linux/cgroup.h:478 [inline]
task_dfl_cgroup include/linux/cgroup.h:547 [inline]
cgroup_account_cputime include/linux/cgroup.h:776 [inline]
update_curr+0x693/0x8d0 kernel/sched/fair.c:860
pick_next_task_fair+0x221/0xc70 kernel/sched/fair.c:6680
pick_next_task kernel/sched/core.c:3921 [inline]
__schedule+0x375/0x1f90 kernel/sched/core.c:4051
schedule+0xdc/0x2b0 kernel/sched/core.c:4155
paste_selection+0x2f5/0x460 drivers/tty/vt/selection.c:367
tioclinux+0x133/0x480 drivers/tty/vt/vt.c:3044
vt_ioctl+0x1a41/0x26d0 drivers/tty/vt/vt_ioctl.c:364
tty_ioctl+0xa37/0x14f0 drivers/tty/tty_io.c:2660
vfs_ioctl fs/ioctl.c:47 [inline]
file_ioctl fs/ioctl.c:545 [inline]
do_vfs_ioctl+0x977/0x14e0 fs/ioctl.c:732
ksys_ioctl+0xab/0xd0 fs/ioctl.c:749
__do_sys_ioctl fs/ioctl.c:756 [inline]
__se_sys_ioctl fs/ioctl.c:754 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
RIP: 0033:0x441219
Code: e8 3c ad 02 00 48 83 c4 18 c3 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 0f 83 9b 09 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fffbf09e3f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000441219
RDX: 00000000200000c0 RSI: 000000000000541c RDI: 0000000000000004
RBP: 000000000008ba8c R08: 000000000000000d R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000402040
R13: 00000000004020d0 R14: 0000000000000000 R15: 0000000000000000

This bug is generated by a bot. It may contain errors.
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For information about bisection process see:
syzbot can test patches for this bug, for details see:

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