INFO: task hung in n_tty_read

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 7d120bf2 Linux 4.19.90
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=15274cc1e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=f97143d0904aeaa
dashboard link: https://syzkaller.appspot.com/bug?extid=916bff519eec470a8375
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+916bff...@syzkaller.appspotmail.com

team0 (unregistering): Port device team_slave_0 removed
bond0 (unregistering): Releasing backup interface bond_slave_1
bond0 (unregistering): Releasing backup interface bond_slave_0
bond0 (unregistering): Released all slaves
INFO: task login:7755 blocked for more than 140 seconds.
Not tainted 4.19.90-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
login D25064 7755 1 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2826 [inline]
__schedule+0x866/0x1dc0 kernel/sched/core.c:3515
schedule+0x92/0x1c0 kernel/sched/core.c:3559
schedule_timeout+0x8c8/0xfc0 kernel/time/timer.c:1782
do_wait_for_common kernel/sched/completion.c:83 [inline]
__wait_for_common kernel/sched/completion.c:104 [inline]
wait_for_common kernel/sched/completion.c:115 [inline]
wait_for_completion+0x29c/0x440 kernel/sched/completion.c:136
__flush_work+0x49f/0x870 kernel/workqueue.c:2926
flush_work+0x18/0x20 kernel/workqueue.c:2947
tty_buffer_flush_work+0x16/0x19 drivers/tty/tty_buffer.c:613
n_tty_read+0xb1a/0x1b70 drivers/tty/n_tty.c:2197
tty_read+0x193/0x2a0 drivers/tty/tty_io.c:867
__vfs_read+0x114/0x800 fs/read_write.c:416
vfs_read+0x194/0x3d0 fs/read_write.c:452
ksys_read+0x14f/0x2d0 fs/read_write.c:579
__do_sys_read fs/read_write.c:589 [inline]
__se_sys_read fs/read_write.c:587 [inline]
__x64_sys_read+0x73/0xb0 fs/read_write.c:587
do_syscall_64+0xfd/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7fa7cd8ce310
Code: Bad RIP value.
RSP: 002b:00007ffff2c09808 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fa7cd8ce310
RDX: 00000000000001ff RSI: 00007ffff2c09a70 RDI: 0000000000000000
RBP: 0000000000000000 R08: 00007fa7ce1b1700 R09: 0000000000000000
R10: 00007ffff2c097c0 R11: 0000000000000246 R12: 00007ffff2c09a70
R13: 0000000000000000 R14: 0000000000000001 R15: 000000000060b798
INFO: task kworker/u4:4:24435 blocked for more than 140 seconds.
Not tainted 4.19.90-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:4 D25776 24435 2 0x80000000
Workqueue: events_unbound flush_to_ldisc
Call Trace:
context_switch kernel/sched/core.c:2826 [inline]
__schedule+0x866/0x1dc0 kernel/sched/core.c:3515
schedule+0x92/0x1c0 kernel/sched/core.c:3559
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3617
__mutex_lock_common kernel/locking/mutex.c:1002 [inline]
__mutex_lock+0x726/0x1300 kernel/locking/mutex.c:1072
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
flush_to_ldisc+0x3d/0x390 drivers/tty/tty_buffer.c:500
process_one_work+0x989/0x1750 kernel/workqueue.c:2153
process_scheduled_works kernel/workqueue.c:2212 [inline]
worker_thread+0x750/0xe40 kernel/workqueue.c:2301
kthread+0x354/0x420 kernel/kthread.c:246
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

Showing all locks held in the system:
1 lock held by khungtaskd/1066:
#0: 0000000051c4ccd0 (rcu_read_lock){....}, at:
debug_show_all_locks+0x5f/0x27e kernel/locking/lockdep.c:4438
1 lock held by rsyslogd/7632:
#0: 0000000059dab9a9 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0xee/0x110
fs/file.c:767
2 locks held by login/7755:
#0: 00000000c9748ef0 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 00000000b8b152dc (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
2 locks held by getty/7756:
#0: 000000005c0562bc (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 000000007939a641 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
2 locks held by getty/7757:
#0: 0000000059023fd5 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 0000000014a5a87d (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
2 locks held by getty/7758:
#0: 00000000eb457927 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 00000000c3b3e4a0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
2 locks held by getty/7759:
#0: 0000000044e29541 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 00000000faeabba2 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
2 locks held by getty/7760:
#0: 0000000087251524 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 00000000a4713372 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
2 locks held by getty/7761:
#0: 00000000bb8cb65c (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 0000000035a91b15 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
3 locks held by kworker/u4:4/24435:
#0: 00000000187c75da ((wq_completion)"events_unbound"){+.+.}, at:
__write_once_size include/linux/compiler.h:220 [inline]
#0: 00000000187c75da ((wq_completion)"events_unbound"){+.+.}, at:
arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
#0: 00000000187c75da ((wq_completion)"events_unbound"){+.+.}, at:
atomic64_set include/asm-generic/atomic-instrumented.h:40 [inline]
#0: 00000000187c75da ((wq_completion)"events_unbound"){+.+.}, at:
atomic_long_set include/asm-generic/atomic-long.h:59 [inline]
#0: 00000000187c75da ((wq_completion)"events_unbound"){+.+.}, at:
set_work_data kernel/workqueue.c:617 [inline]
#0: 00000000187c75da ((wq_completion)"events_unbound"){+.+.}, at:
set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
#0: 00000000187c75da ((wq_completion)"events_unbound"){+.+.}, at:
process_one_work+0x87e/0x1750 kernel/workqueue.c:2124
#1: 00000000a4b91a4c ((work_completion)(&buf->work)){+.+.}, at:
process_one_work+0x8b4/0x1750 kernel/workqueue.c:2128
#2: 00000000d3543cfd (&buf->lock){+.+.}, at: flush_to_ldisc+0x3d/0x390
drivers/tty/tty_buffer.c:500
2 locks held by syz-executor.2/31579:

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

NMI backtrace for cpu 1
CPU: 1 PID: 1066 Comm: khungtaskd Not tainted 4.19.90-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+0x63/0xa4 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x1b0/0x1f8 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:203 [inline]
watchdog+0x9df/0xee0 kernel/hung_task.c:287
kthread+0x354/0x420 kernel/kthread.c:246
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 4962 Comm: kworker/u4:10 Not tainted 4.19.90-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: (null) (bat_events)
RIP: 0010:account_entity_dequeue+0x1bf/0x4b0 kernel/sched/fair.c:2772
Code: f8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 1c 02 00 00 41 c7 85 98
00 00 00 00 00 00 00 e9 ff fe ff ff 48 8d bb 70 01 00 00 <48> b8 00 00 00
00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f
RSP: 0018:ffff888090d97c30 EFLAGS: 00000046
RAX: dffffc0000000000 RBX: ffff8880ae82c300 RCX: 0000000000000d73
RDX: 1ffff11013e558d4 RSI: ffff88809f2ac540 RDI: ffff8880ae82c470
RBP: ffff888090d97c60 R08: ffff88809f2ac550 R09: ffffed1015d04733
R10: ffffed1015d04732 R11: ffff8880ae823993 R12: ffff88809f2ac540
R13: ffff8880ae82c240 R14: 0000000000100000 R15: ffff88809f2ac540
FS: 0000000000000000(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000130 CR3: 000000005c376000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Call Trace:
dequeue_entity+0x230/0xf40 kernel/sched/fair.c:4039
dequeue_task_fair+0x65/0x6f0 kernel/sched/fair.c:5181
dequeue_task kernel/sched/core.c:739 [inline]
deactivate_task+0xd3/0x340 kernel/sched/core.c:755
__schedule+0x2e5/0x1dc0 kernel/sched/core.c:3465
schedule+0x92/0x1c0 kernel/sched/core.c:3559
worker_thread+0x248/0xe40 kernel/workqueue.c:2317
kthread+0x354/0x420 kernel/kthread.c:246
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415


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[syzbot]

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