Hello,
We found the following issue using syzkaller on Linux v6.10.
In `tty_buffer_flush`, the task hangs when trying to acquire lock
`buf->lock`.
Unfortunately, the syzkaller failed to generate a reproducer.
But at least we have the report:
INFO: task kworker/0:5:8495 blocked for more than 143 seconds.
Not tainted 6.10.0 #13
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/0:5 state:D stack:24400 pid:8495 tgid:8495 ppid:2
flags:0x00004000
Workqueue: events vc_SAK
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5407 [inline]
__schedule+0xf4a/0x15e0 kernel/sched/core.c:6748
__schedule_loop kernel/sched/core.c:6825 [inline]
schedule+0x143/0x310 kernel/sched/core.c:6840
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:6897
__mutex_lock_common kernel/locking/mutex.c:684 [inline]
__mutex_lock+0x69a/0xd50 kernel/locking/mutex.c:752
tty_buffer_flush+0x75/0x3f0 drivers/tty/tty_buffer.c:229
tty_ldisc_flush+0x66/0xc0 drivers/tty/tty_ldisc.c:388
__do_SAK+0xc4/0x710 drivers/tty/tty_io.c:3038
vc_SAK+0x73/0x210 drivers/tty/vt/vt_ioctl.c:993
process_one_work kernel/workqueue.c:3248 [inline]
process_scheduled_works+0x977/0x1410 kernel/workqueue.c:3329
worker_thread+0xaa0/0x1020 kernel/workqueue.c:3409
kthread+0x2eb/0x380 kernel/kthread.c:389
ret_from_fork+0x49/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:244
</TASK>
INFO: task kworker/u4:27:17406 blocked for more than 143 seconds.
Not tainted 6.10.0 #13
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/u4:27 state:D stack:20472 pid:17406 tgid:17406 ppid:2
flags:0x00004000
Workqueue: events_unbound flush_to_ldisc
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5407 [inline]
__schedule+0xf4a/0x15e0 kernel/sched/core.c:6748
__schedule_loop kernel/sched/core.c:6825 [inline]
schedule+0x143/0x310 kernel/sched/core.c:6840
schedule_timeout+0xac/0x300 kernel/time/timer.c:2557
___down_common kernel/locking/semaphore.c:225 [inline]
__down_common+0x31c/0x510 kernel/locking/semaphore.c:246
down+0x7e/0xb0 kernel/locking/semaphore.c:63
console_lock+0x140/0x1a0 kernel/printk/printk.c:2665
con_flush_chars+0x67/0x260 drivers/tty/vt/vt.c:3503
__receive_buf drivers/tty/n_tty.c:1644 [inline]
n_tty_receive_buf_common+0xd30/0x1370 drivers/tty/n_tty.c:1739
tty_port_default_receive_buf+0x69/0x90 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:445 [inline]
flush_to_ldisc+0x2ef/0x850 drivers/tty/tty_buffer.c:495
process_one_work kernel/workqueue.c:3248 [inline]
process_scheduled_works+0x977/0x1410 kernel/workqueue.c:3329
worker_thread+0xaa0/0x1020 kernel/workqueue.c:3409
kthread+0x2eb/0x380 kernel/kthread.c:389
ret_from_fork+0x49/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:244
</TASK>
INFO: task syz.0.1346:24748 blocked for more than 143 seconds.
Not tainted 6.10.0 #13
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.1346 state:D stack:24680 pid:24748 tgid:24748
ppid:22281 flags:0x00000004
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5407 [inline]
__schedule+0xf4a/0x15e0 kernel/sched/core.c:6748
__schedule_loop kernel/sched/core.c:6825 [inline]
schedule+0x143/0x310 kernel/sched/core.c:6840
schedule_timeout+0xac/0x300 kernel/time/timer.c:2557
___down_common kernel/locking/semaphore.c:225 [inline]
__down_common+0x31c/0x510 kernel/locking/semaphore.c:246
down+0x7e/0xb0 kernel/locking/semaphore.c:63
console_lock+0x140/0x1a0 kernel/printk/printk.c:2665
con_shutdown+0x44/0x80 drivers/tty/vt/vt.c:3567
release_tty+0xbf/0x560 drivers/tty/tty_io.c:1595
tty_release_struct+0xb8/0xd0 drivers/tty/tty_io.c:1707
tty_release+0xb66/0xd70 drivers/tty/tty_io.c:1867
__fput+0x24a/0x8a0 fs/file_table.c:422
task_work_run+0x239/0x2f0 kernel/task_work.c:180
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
syscall_exit_to_user_mode+0x12d/0x280 kernel/entry/common.c:218
do_syscall_64+0x8a/0x150 arch/x86/entry/common.c:89
entry_SYSCALL_64_after_hwframe+0x67/0x6f
RIP: 0033:0x7faaf81809b9
RSP: 002b:00007ffd386bad68 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007faaf8347a80 RCX: 00007faaf81809b9
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007faaf8347a80 R08: 0000000000000006 R09: 00007ffd386bb04f
R10: 00000000003ffc40 R11: 0000000000000246 R12: 000000000009e184
R13: 00007ffd386bae60 R14: 00007ffd386bae80 R15: ffffffffffffffff
</TASK>
INFO: task syz.0.1346:24760 blocked for more than 143 seconds.
Not tainted 6.10.0 #13
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.1346 state:D stack:27400 pid:24760 tgid:24748
ppid:22281 flags:0x00004006
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5407 [inline]
__schedule+0xf4a/0x15e0 kernel/sched/core.c:6748
__schedule_loop kernel/sched/core.c:6825 [inline]
schedule+0x143/0x310 kernel/sched/core.c:6840
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:6897
__mutex_lock_common kernel/locking/mutex.c:684 [inline]
__mutex_lock+0x69a/0xd50 kernel/locking/mutex.c:752
tty_release_struct+0xad/0xd0 drivers/tty/tty_io.c:1706
tty_release+0xb66/0xd70 drivers/tty/tty_io.c:1867
__fput+0x24a/0x8a0 fs/file_table.c:422
task_work_run+0x239/0x2f0 kernel/task_work.c:180
get_signal+0x15d5/0x1730 kernel/signal.c:2681
arch_do_signal_or_restart+0x92/0x7f0 arch/x86/kernel/signal.c:310
exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
syscall_exit_to_user_mode+0x95/0x280 kernel/entry/common.c:218
do_syscall_64+0x8a/0x150 arch/x86/entry/common.c:89
entry_SYSCALL_64_after_hwframe+0x67/0x6f
RIP: 0033:0x7faaf81809b9
RSP: 002b:00007faaf9013038 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: 0000000000000000 RBX: 00007faaf8346058 RCX: 00007faaf81809b9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007faaf81f4f70 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007faaf8346058 R15: 00007ffd386bac08
</TASK>
INFO: task syz.1.1347:24771 blocked for more than 143 seconds.
Not tainted 6.10.0 #13
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.1.1347 state:D stack:24680 pid:24771 tgid:24771
ppid:19241 flags:0x00004004
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5407 [inline]
__schedule+0xf4a/0x15e0 kernel/sched/core.c:6748
__schedule_loop kernel/sched/core.c:6825 [inline]
schedule+0x143/0x310 kernel/sched/core.c:6840
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:6897
__mutex_lock_common kernel/locking/mutex.c:684 [inline]
__mutex_lock+0x69a/0xd50 kernel/locking/mutex.c:752
tty_release_struct+0xad/0xd0 drivers/tty/tty_io.c:1706
tty_release+0xb66/0xd70 drivers/tty/tty_io.c:1867
__fput+0x24a/0x8a0 fs/file_table.c:422
task_work_run+0x239/0x2f0 kernel/task_work.c:180
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
syscall_exit_to_user_mode+0x12d/0x280 kernel/entry/common.c:218
do_syscall_64+0x8a/0x150 arch/x86/entry/common.c:89
entry_SYSCALL_64_after_hwframe+0x67/0x6f
RIP: 0033:0x7f80957809b9
RSP: 002b:00007fff493e0918 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007f8095947a80 RCX: 00007f80957809b9
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007f8095947a80 R08: 0000000000000006 R09: 00007fff493e0bff
R10: 00000000003ffc0c R11: 0000000000000246 R12: 000000000009e315
R13: 00007fff493e0a10 R14: 00007fff493e0a30 R15: ffffffffffffffff
</TASK>
INFO: task syz.1.1347:24776 blocked for more than 143 seconds.
Not tainted 6.10.0 #13
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.1.1347 state:D stack:27400 pid:24776 tgid:24771
ppid:19241 flags:0x00000004
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5407 [inline]
__schedule+0xf4a/0x15e0 kernel/sched/core.c:6748
__schedule_loop kernel/sched/core.c:6825 [inline]
schedule+0x143/0x310 kernel/sched/core.c:6840
schedule_timeout+0xac/0x300 kernel/time/timer.c:2557
___down_common kernel/locking/semaphore.c:225 [inline]
__down_common+0x31c/0x510 kernel/locking/semaphore.c:246
down+0x7e/0xb0 kernel/locking/semaphore.c:63
console_lock+0x140/0x1a0 kernel/printk/printk.c:2665
do_con_write+0x150/0x4ca0 drivers/tty/vt/vt.c:3056
con_write+0x22/0x40 drivers/tty/vt/vt.c:3434
process_output_block drivers/tty/n_tty.c:574 [inline]
n_tty_write+0xda5/0x12d0 drivers/tty/n_tty.c:2389
iterate_tty_write drivers/tty/tty_io.c:1021 [inline]
file_tty_write+0x589/0xa00 drivers/tty/tty_io.c:1096
new_sync_write fs/read_write.c:497 [inline]
vfs_write+0x8a1/0xc70 fs/read_write.c:590
ksys_write+0x19b/0x2c0 fs/read_write.c:643
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x7e/0x150 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x67/0x6f
RIP: 0033:0x7f80957809b9
RSP: 002b:00007f80951ff038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f8095946058 RCX: 00007f80957809b9
RDX: 000000000000fdef RSI: 0000000020000000 RDI: 0000000000000005
RBP: 00007f80957f4f70 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f8095946058 R15: 00007fff493e07b8
</TASK>
INFO: lockdep is turned off.
NMI backtrace for cpu 0
CPU: 0 PID: 25 Comm: khungtaskd Not tainted 6.10.0 #13
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x23d/0x360 lib/dump_stack.c:114
nmi_cpu_backtrace+0x451/0x480 lib/nmi_backtrace.c:113
nmi_trigger_cpumask_backtrace+0x181/0x2d0 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:162 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:223 [inline]
watchdog+0xdbd/0xe00 kernel/hung_task.c:379
kthread+0x2eb/0x380 kernel/kthread.c:389
ret_from_fork+0x49/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:244
</TASK>
