INFO: task hung in tty_buffer_flush (3)

Status: auto-obsoleted due to no activity on 2026/06/27 15:16
Subsystems: serial
Labels: prio:high
[Documentation on labels]
First crash: 208d, last: 160d
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
305e42ac assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ✅ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ INFO: task hung in tty_buffer_flush (3) 2026/05/22 03:44 2026/05/22 03:44 2026/05/22 04:24 d5742584
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: task hung in tty_buffer_flush serial 1 6 533d 621d 0/29 auto-obsoleted due to no activity on 2025/06/19 19:00
upstream INFO: task hung in tty_buffer_flush (2) serial 1 1 430d 430d 0/29 auto-obsoleted due to no activity on 2025/09/30 11:42

Sample crash report:
INFO: task kworker/0:0:9 blocked for more than 143 seconds.
      Tainted: G             L      syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/0:0     state:D stack:19360 pid:9     tgid:9     ppid:2      task_flags:0x4208060 flags:0x00080000
Workqueue: events vc_SAK
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5298 [inline]
 __schedule+0x15dd/0x52d0 kernel/sched/core.c:6911
 __schedule_loop kernel/sched/core.c:6993 [inline]
 schedule+0x164/0x360 kernel/sched/core.c:7008
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7065
 __mutex_lock_common kernel/locking/mutex.c:692 [inline]
 __mutex_lock+0x7fe/0x1300 kernel/locking/mutex.c:776
 tty_buffer_flush+0x74/0x2b0 drivers/tty/tty_buffer.c:229
 tty_ldisc_flush+0x6b/0xc0 drivers/tty/tty_ldisc.c:388
 __do_SAK+0xf2/0x6e0 drivers/tty/tty_io.c:3025
 vc_SAK+0x78/0x220 drivers/tty/vt/vt_ioctl.c:994
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
INFO: task kworker/u8:9:1120 blocked for more than 143 seconds.
      Tainted: G             L      syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/u8:9    state:D stack:20240 pid:1120  tgid:1120  ppid:2      task_flags:0x4208060 flags:0x00080000
Workqueue: events_unbound flush_to_ldisc
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5298 [inline]
 __schedule+0x15dd/0x52d0 kernel/sched/core.c:6911
 __schedule_loop kernel/sched/core.c:6993 [inline]
 schedule+0x164/0x360 kernel/sched/core.c:7008
 schedule_timeout+0xc3/0x2c0 kernel/time/sleep_timeout.c:75
 ___down_common kernel/locking/semaphore.c:268 [inline]
 __down_common+0x321/0x730 kernel/locking/semaphore.c:293
 down+0x80/0xd0 kernel/locking/semaphore.c:100
 console_lock+0x58/0x90 kernel/printk/printk.c:2896
 class_console_lock_constructor include/linux/console.h:736 [inline]
 do_con_write+0x124/0x5300 drivers/tty/vt/vt.c:3195
 con_put_char+0x82/0xc0 drivers/tty/vt/vt.c:3574
 tty_put_char+0xce/0x160 drivers/tty/tty_io.c:3153
 do_output_char+0x6ac/0x970 drivers/tty/n_tty.c:459
 __process_echoes+0x2e1/0xa20 drivers/tty/n_tty.c:697
 process_echoes drivers/tty/n_tty.c:767 [inline]
 n_tty_receive_char_flow_ctrl drivers/tty/n_tty.c:1225 [inline]
 n_tty_receive_char_special drivers/tty/n_tty.c:1335 [inline]
 n_tty_receive_buf_standard+0xc53/0x6c00 drivers/tty/n_tty.c:1580
 __receive_buf drivers/tty/n_tty.c:1616 [inline]
 n_tty_receive_buf_common+0xa87/0x1300 drivers/tty/n_tty.c:1715
 tty_port_default_receive_buf+0x6e/0xa0 drivers/tty/tty_port.c:37
 receive_buf drivers/tty/tty_buffer.c:445 [inline]
 flush_to_ldisc+0x24a/0x6e0 drivers/tty/tty_buffer.c:495
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
INFO: task kworker/0:6:5904 blocked for more than 143 seconds.
      Tainted: G             L      syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/0:6     state:D stack:21576 pid:5904  tgid:5904  ppid:2      task_flags:0x4208160 flags:0x00080000
Workqueue: events console_callback
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5298 [inline]
 __schedule+0x15dd/0x52d0 kernel/sched/core.c:6911
 __schedule_loop kernel/sched/core.c:6993 [inline]
 schedule+0x164/0x360 kernel/sched/core.c:7008
 schedule_timeout+0xc3/0x2c0 kernel/time/sleep_timeout.c:75
 ___down_common kernel/locking/semaphore.c:268 [inline]
 __down_common+0x321/0x730 kernel/locking/semaphore.c:293
 down+0x80/0xd0 kernel/locking/semaphore.c:100
 console_lock+0x58/0x90 kernel/printk/printk.c:2896
 class_console_lock_constructor include/linux/console.h:736 [inline]
 console_callback+0x69/0x450 drivers/tty/vt/vt.c:3257
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
INFO: lockdep is turned off.
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 31 Comm: khungtaskd Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 nmi_cpu_backtrace+0x274/0x2d0 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x17a/0x300 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:161 [inline]
 __sys_info lib/sys_info.c:157 [inline]
 sys_info+0x135/0x170 lib/sys_info.c:165
 check_hung_uninterruptible_tasks kernel/hung_task.c:346 [inline]
 watchdog+0xfd9/0x1030 kernel/hung_task.c:515
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 18612 Comm: syz.7.2462 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:folio_get include/linux/mm.h:1778 [inline]
RIP: 0010:__folio_batch_add_and_move+0x66/0xc50 mm/swap.c:187
Code: 00 4c 89 e8 48 c1 e8 03 0f b6 04 18 84 c0 0f 85 80 09 00 00 41 8b 6d 00 83 c5 7f bf 80 00 00 00 89 ee e8 1d e8 c0 ff 83 fd 7f <0f> 86 00 0b 00 00 4c 89 ef be 04 00 00 00 e8 87 34 2b 00 f0 41 ff
RSP: 0018:ffffc90010487838 EFLAGS: 00000212
RAX: ffffffff8204caf3 RBX: dffffc0000000000 RCX: 0000000000000002
RDX: ffff88809c80db80 RSI: 0000000000000081 RDI: 0000000000000080
RBP: 0000000000000081 R08: ffffea00010c78f7 R09: 1ffffd4000218f1e
R10: dffffc0000000000 R11: fffff94000218f1f R12: ffffea00010c78c0
R13: ffffea00010c78f4 R14: 0000000000000000 R15: ffffffff931da9e8
FS:  00007f9c4644f6c0(0000) GS:ffff888125459000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f9c3b2023b2 CR3: 0000000089f33000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
 shmem_alloc_and_add_folio+0xce0/0xf80 mm/shmem.c:2031
 shmem_get_folio_gfp+0x5a9/0x1670 mm/shmem.c:2567
 shmem_get_folio mm/shmem.c:2673 [inline]
 shmem_write_begin+0x16c/0x330 mm/shmem.c:3327
 generic_perform_write+0x2e2/0x8f0 mm/filemap.c:4319
 shmem_file_write_iter+0xf8/0x120 mm/shmem.c:3502
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x61d/0xb90 fs/read_write.c:688
 ksys_write+0x150/0x270 fs/read_write.c:740
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9c4555cfce
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007f9c4644eda8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f9c4644f6c0 RCX: 00007f9c4555cfce
RDX: 0000000000002c00 RSI: 00007f9c3b200000 RDI: 0000000000000005
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000005
R13: 00007f9c4644eee0 R14: 00007f9c4644eea0 R15: 00007f9c3b200000
 </TASK>

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/03/29 15:08 upstream cbfffcca2bf0 356bdfc9 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: task hung in tty_buffer_flush
2026/02/09 21:41 linux-next 132737e360b4 df949cd9 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce INFO: task hung in tty_buffer_flush
* Struck through repros no longer work on HEAD.