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SubjectINFO: task hung in flush_to_ldisc
From
Hello,

syzbot found the following crash on:

HEAD commit: 63de3747 Merge tag 'tag-chrome-platform-for-v5.5' of git:/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10e7d59ce00000
kernel config: https://syzkaller.appspot.com/x/.config?x=1d189d07c6717979
dashboard link: https://syzkaller.appspot.com/bug?extid=e199b43b49192126ff69
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+e199b43b49192126ff69@syzkaller.appspotmail.com

INFO: task kworker/u4:0:7 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.
kworker/u4:0 D24280 7 2 0x80004000
Workqueue: events_unbound flush_to_ldisc
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_preempt_disabled+0x13/0x20 kernel/sched/core.c:4214
__mutex_lock_common kernel/locking/mutex.c:1036 [inline]
__mutex_lock+0x7ab/0x13c0 kernel/locking/mutex.c:1106
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1121
flush_to_ldisc+0x3d/0x390 drivers/tty/tty_buffer.c:505
process_one_work+0x9af/0x1740 kernel/workqueue.c:2264
worker_thread+0x98/0xe40 kernel/workqueue.c:2410
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
INFO: task login:9555 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 D23224 9555 1 0x00000004
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
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+0x4fe/0xa50 kernel/workqueue.c:3041
flush_work+0x18/0x20 kernel/workqueue.c:3062
tty_buffer_flush_work+0x16/0x20 drivers/tty/tty_buffer.c:618
n_tty_read+0xb1c/0x1c10 drivers/tty/n_tty.c:2199
tty_read+0x1a0/0x2a0 drivers/tty/tty_io.c:869
__vfs_read+0x8a/0x110 fs/read_write.c:425
vfs_read+0x1f0/0x440 fs/read_write.c:461
ksys_read+0x14f/0x290 fs/read_write.c:587
__do_sys_read fs/read_write.c:597 [inline]
__se_sys_read fs/read_write.c:595 [inline]
__x64_sys_read+0x73/0xb0 fs/read_write.c:595
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7f9a079ec310
Code: Bad RIP value.
RSP: 002b:00007ffd2af2dca8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f9a079ec310
RDX: 00000000000001ff RSI: 00007ffd2af2df10 RDI: 0000000000000000
RBP: 0000000000000000 R08: 00007f9a082cf700 R09: 0000000000000000
R10: 00007ffd2af2dc60 R11: 0000000000000246 R12: 00007ffd2af2df10
R13: 0000000000000000 R14: 0000000000000001 R15: 000000000060b798

Showing all locks held in the system:
3 locks held by kworker/u4:0/7:
#0: ffff8880aa433928 ((wq_completion)events_unbound){+.+.}, at:
__write_once_size include/linux/compiler.h:226 [inline]
#0: ffff8880aa433928 ((wq_completion)events_unbound){+.+.}, at:
arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
#0: ffff8880aa433928 ((wq_completion)events_unbound){+.+.}, at:
atomic64_set include/asm-generic/atomic-instrumented.h:855 [inline]
#0: ffff8880aa433928 ((wq_completion)events_unbound){+.+.}, at:
atomic_long_set include/asm-generic/atomic-long.h:40 [inline]
#0: ffff8880aa433928 ((wq_completion)events_unbound){+.+.}, at:
set_work_data kernel/workqueue.c:615 [inline]
#0: ffff8880aa433928 ((wq_completion)events_unbound){+.+.}, at:
set_work_pool_and_clear_pending kernel/workqueue.c:642 [inline]
#0: ffff8880aa433928 ((wq_completion)events_unbound){+.+.}, at:
process_one_work+0x88b/0x1740 kernel/workqueue.c:2235
#1: ffffc90000cdfdc0 ((work_completion)(&buf->work)){+.+.}, at:
process_one_work+0x8c1/0x1740 kernel/workqueue.c:2239
#2: ffff8880aa5bc0a8 (&buf->lock){+.+.}, at: flush_to_ldisc+0x3d/0x390
drivers/tty/tty_buffer.c:505
1 lock held by khungtaskd/1115:
#0: ffffffff897a4080 (rcu_read_lock){....}, at:
debug_show_all_locks+0x5f/0x279 kernel/locking/lockdep.c:5334
1 lock held by rsyslogd/9433:
#0: ffff8880a36c8620 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0xee/0x110
fs/file.c:801
2 locks held by login/9555:
#0: ffff8880a0baa090 (&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+0x232/0x1c10 drivers/tty/n_tty.c:2156
2 locks held by getty/9556:
#0: ffff8880a6ce8090 (&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+0x232/0x1c10 drivers/tty/n_tty.c:2156
2 locks held by getty/9558:
#0: ffff8880a3bc9090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc900018f32e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1c10 drivers/tty/n_tty.c:2156
2 locks held by getty/9559:
#0: ffff8880949a6090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc900019132e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1c10 drivers/tty/n_tty.c:2156
2 locks held by getty/9560:
#0: ffff88809f429090 (&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+0x232/0x1c10 drivers/tty/n_tty.c:2156
2 locks held by getty/9561:
#0: ffff888096165090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc900018632e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1c10 drivers/tty/n_tty.c:2156
2 locks held by syz-executor.3/16730:
#0: ffff8880a0baa090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffff8880aa5bc0a8 (&buf->lock){+.+.}, at:
tty_buffer_lock_exclusive+0x30/0x40 drivers/tty/tty_buffer.c:61
2 locks held by getty/17086:
#0: ffff8880a8418090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc90002c9b2e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1c10 drivers/tty/n_tty.c:2156

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

NMI backtrace for cpu 0
CPU: 0 PID: 1115 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 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 16730 Comm: syz-executor.3 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:lock_is_held_type+0x220/0x320 kernel/locking/lockdep.c:4523
Code: e0 03 3b 45 cc 41 0f 94 c4 65 48 8b 1c 25 c0 1e 02 00 48 8d bb 94 08
00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> b6 14 02 48
89 f8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 d3
RSP: 0018:ffffc90002b5f6a8 EFLAGS: 00000807
RAX: dffffc0000000000 RBX: ffff888057b10300 RCX: ffff888057b10b98
RDX: 1ffff1100af62172 RSI: ffff8880ae937398 RDI: ffff888057b10b94
RBP: ffffc90002b5f6f0 R08: 1ffff1100af62060 R09: ffffed100af62061
R10: ffffed100af62060 R11: ffff888057b10307 R12: 0000000000000001
R13: ffff888057b10be8 R14: ffff8880ae937398 R15: 0000000000000002
FS: 00007fd84687b700(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c43a311010 CR3: 0000000094d79000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
lock_is_held include/linux/lockdep.h:361 [inline]
rq_clock_task kernel/sched/sched.h:1104 [inline]
update_curr+0x296/0x8d0 kernel/sched/fair.c:835
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
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a679
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:00007fd84687ac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a679
RDX: 0000000020000000 RSI: 000000000000541c RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fd84687b6d4
R13: 00000000004c5962 R14: 00000000004dbb78 R15: 00000000ffffffff


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

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