syzbot


INFO: task hung in flush_to_ldisc

Status: auto-closed as invalid on 2020/06/15 14:09
Reported-by: syzbot+bc44024ce696c8867cba@syzkaller.appspotmail.com
First crash: 1022d, last: 960d
similar bugs (8):
Kernel Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-4.19 INFO: task hung in flush_to_ldisc (2) 1 811d 811d 0/1 auto-closed as invalid on 2020/11/11 17:44
upstream INFO: task hung in flush_to_ldisc (2) 1 541d 541d 0/24 auto-closed as invalid on 2021/06/09 11:04
upstream INFO: task hung in flush_to_ldisc C inconclusive done 15 962d 1032d 17/24 fixed on 2020/11/16 12:12
linux-4.14 INFO: task hung in flush_to_ldisc (3) 1 573d 573d 0/1 auto-closed as invalid on 2021/07/07 16:40
upstream INFO: task hung in flush_to_ldisc (3) C inconclusive 3 242d 431d 0/24 closed as invalid on 2022/02/08 10:26
linux-4.14 INFO: task hung in flush_to_ldisc (2) 1 764d 764d 0/1 auto-closed as invalid on 2020/12/28 13:53
linux-4.19 INFO: task hung in flush_to_ldisc (3) 1 525d 525d 0/1 auto-closed as invalid on 2021/08/25 00:39
linux-4.14 INFO: task hung in flush_to_ldisc 8 952d 1023d 0/1 auto-closed as invalid on 2020/06/23 11:01

Sample crash report:
INFO: task kworker/u4:0:13246 blocked for more than 140 seconds.
      Not tainted 4.19.104-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:0    D25568 13246      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
 worker_thread+0x98/0xe40 kernel/workqueue.c:2296
 kthread+0x354/0x420 kernel/kthread.c:246
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415
INFO: task getty:20061 blocked for more than 140 seconds.
      Not tainted 4.19.104-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
getty           D27720 20061      1 0x00000000
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: 0033:0x7f4815daa310
Code: Bad RIP value.
RSP: 002b:00007ffddc614cd8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007f481647f6a8 RCX: 00007f4815daa310
RDX: 0000000000000001 RSI: 00007ffddc614d28 RDI: 0000000000000000
RBP: 00007ffddc615510 R08: 0000000000000000 R09: 00007f481647f700
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006075a0
R13: 00007ffddc617eda R14: 0000000000000000 R15: 0000000000000000

Showing all locks held in the system:
1 lock held by khungtaskd/1080:
 #0: 000000005aa21001 (rcu_read_lock){....}, at: debug_show_all_locks+0x5f/0x27e kernel/locking/lockdep.c:4438
1 lock held by rsyslogd/7790:
 #0: 0000000067fda98a (&f->f_pos_lock){+.+.}, at: __fdget_pos+0xee/0x110 fs/file.c:767
2 locks held by getty/7913:
 #0: 000000003c1aeae9 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
 #1: 000000002f1c1b2c (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
2 locks held by getty/7914:
 #0: 000000000b24d01c (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
 #1: 0000000019c1e0d2 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
2 locks held by getty/7915:
 #0: 00000000625ceac9 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
 #1: 000000002dad0646 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
2 locks held by getty/7916:
 #0: 00000000b07210e3 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
 #1: 000000003ac313ca (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
2 locks held by getty/7917:
 #0: 0000000024eff389 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
 #1: 00000000b4fc8cbe (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
2 locks held by getty/7918:
 #0: 000000003adf4022 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
 #1: 000000006a006c79 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
3 locks held by kworker/u4:0/13246:
 #0: 00000000997e0484 ((wq_completion)"events_unbound"){+.+.}, at: __write_once_size include/linux/compiler.h:220 [inline]
 #0: 00000000997e0484 ((wq_completion)"events_unbound"){+.+.}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: 00000000997e0484 ((wq_completion)"events_unbound"){+.+.}, at: atomic64_set include/asm-generic/atomic-instrumented.h:40 [inline]
 #0: 00000000997e0484 ((wq_completion)"events_unbound"){+.+.}, at: atomic_long_set include/asm-generic/atomic-long.h:59 [inline]
 #0: 00000000997e0484 ((wq_completion)"events_unbound"){+.+.}, at: set_work_data kernel/workqueue.c:617 [inline]
 #0: 00000000997e0484 ((wq_completion)"events_unbound"){+.+.}, at: set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
 #0: 00000000997e0484 ((wq_completion)"events_unbound"){+.+.}, at: process_one_work+0x87e/0x1750 kernel/workqueue.c:2124
 #1: 0000000011939d2d ((work_completion)(&buf->work)){+.+.}, at: process_one_work+0x8b4/0x1750 kernel/workqueue.c:2128
 #2: 00000000a1a408a8 (&buf->lock){+.+.}, at: flush_to_ldisc+0x3d/0x390 drivers/tty/tty_buffer.c:500
2 locks held by kworker/u4:2/28730:
 #0: 000000005a8d2e8b (&rq->lock){-.-.}, at: rq_lock kernel/sched/sched.h:1817 [inline]
 #0: 000000005a8d2e8b (&rq->lock){-.-.}, at: __schedule+0x1f8/0x1dc0 kernel/sched/core.c:3453
 #1: 000000005aa21001 (rcu_read_lock){....}, at: trace_sched_stat_runtime include/trace/events/sched.h:428 [inline]
 #1: 000000005aa21001 (rcu_read_lock){....}, at: update_curr+0x2cc/0x8a0 kernel/sched/fair.c:844
2 locks held by getty/20061:
 #0: 00000000e200e7f0 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
 #1: 000000006a3dbecc (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
2 locks held by syz-executor.4/1730:

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

NMI backtrace for cpu 0
CPU: 0 PID: 1080 Comm: khungtaskd Not tainted 4.19.104-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 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 1730 Comm: syz-executor.4 Not tainted 4.19.104-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:789 [inline]
RIP: 0010:lock_is_held_type+0x17e/0x210 kernel/locking/lockdep.c:3943
Code: 00 00 00 fc ff df 41 c7 85 7c 08 00 00 00 00 00 00 48 c1 e8 03 80 3c 10 00 75 63 48 83 3d e1 c2 a0 07 00 74 30 48 89 df 57 9d <0f> 1f 44 00 00 48 83 c4 08 44 89 e0 5b 41 5c 41 5d 5d c3 48 83 c4
RSP: 0018:ffff88809750f640 EFLAGS: 00000082
RAX: 1ffffffff11e4ae9 RBX: 0000000000000082 RCX: ffff888046858d00
RDX: dffffc0000000000 RSI: ffffffff88fb7f40 RDI: 0000000000000082
RBP: ffff88809750f660 R08: 1ffff11015d24732 R09: ffffed1015d24733
R10: ffffed1015d24732 R11: ffff8880ae923993 R12: 0000000000000000
R13: ffff888046858480 R14: ffff888046858480 R15: 0000000000000000
FS:  00007fe0e3a9e700(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffff600400 CR3: 0000000094d03000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 lock_is_held include/linux/lockdep.h:344 [inline]
 task_css include/linux/cgroup.h:482 [inline]
 task_ca kernel/sched/cpuacct.c:43 [inline]
 cpuacct_charge+0x273/0x360 kernel/sched/cpuacct.c:349
 cgroup_account_cputime include/linux/cgroup.h:766 [inline]
 update_curr+0x2d7/0x8a0 kernel/sched/fair.c:845
 pick_next_task_fair+0x6bf/0x1580 kernel/sched/fair.c:6737
 pick_next_task kernel/sched/core.c:3361 [inline]
 __schedule+0x456/0x1dc0 kernel/sched/core.c:3489
 schedule+0x92/0x1c0 kernel/sched/core.c:3559
 paste_selection+0x2e8/0x443 drivers/tty/vt/selection.c:354
 tioclinux+0x133/0x470 drivers/tty/vt/vt.c:3019
 vt_ioctl+0x19ab/0x2530 drivers/tty/vt/vt_ioctl.c:364
 tty_ioctl+0x7f3/0x1510 drivers/tty/tty_io.c:2669
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:501 [inline]
 do_vfs_ioctl+0xd5f/0x1380 fs/ioctl.c:688
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:705
 __do_sys_ioctl fs/ioctl.c:712 [inline]
 __se_sys_ioctl fs/ioctl.c:710 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:710
 do_syscall_64+0xfd/0x620 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c6c9
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fe0e3a9dc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fe0e3a9e6d4 RCX: 000000000045c6c9
RDX: 0000000020000040 RSI: 000000000000541c RDI: 0000000000000004
RBP: 000000000076bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000570 R14: 00000000004c7ec2 R15: 000000000076bf2c

Crashes (10):
Manager Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Title
ci2-linux-4-19 2020/02/16 14:08 linux-4.19.y 9b15f7fae677 cf914200 .config log report
ci2-linux-4-19 2020/02/12 05:41 linux-4.19.y 357668399cf7 a75b198c .config log report
ci2-linux-4-19 2020/02/07 07:46 linux-4.19.y b499cf4b3a90 06150bf1 .config log report
ci2-linux-4-19 2020/02/04 07:01 linux-4.19.y 32ee7492f104 93e5e335 .config log report
ci2-linux-4-19 2020/01/25 22:37 linux-4.19.y d183c8e2647a f4e7270e .config log report
ci2-linux-4-19 2020/01/17 21:40 linux-4.19.y dc4ba5be1bab 3de7aabb .config log report
ci2-linux-4-19 2020/01/15 15:56 linux-4.19.y db5b9190ff82 069a5a44 .config log report
ci2-linux-4-19 2020/01/15 03:09 linux-4.19.y db5b9190ff82 fa12bd3c .config log report
ci2-linux-4-19 2020/01/12 16:51 linux-4.19.y dcd888983542 31290a45 .config log report
ci2-linux-4-19 2019/12/16 06:33 linux-4.19.y 312017a460d5 eef6e580 .config log report
* Struck through repros no longer work on HEAD.