INFO: task hung in commit_echoes

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 0fbc4aeabc91 Merge branch 'x86-urgent-for-linus' of git://..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14c98494400000
kernel config: https://syzkaller.appspot.com/x/.config?x=a63be0c83e84d370
dashboard link: https://syzkaller.appspot.com/bug?extid=bfbf83c6b3961247ed48
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
CC: [gre...@linuxfoundation.org jsl...@suse.com
linux-...@vger.kernel.org]

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+bfbf83...@syzkaller.appspotmail.com

FAT-fs (loop6): Filesystem has been set read-only
FAT-fs (loop6): error, fat_free: invalid cluster chain (i_pos 1041)
INFO: task kworker/u4:7:28378 blocked for more than 120 seconds.
Not tainted 4.18.0-rc2+ #124
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:7 D22456 28378 2 0x80000000
Workqueue: events_unbound flush_to_ldisc
Call Trace:
context_switch kernel/sched/core.c:2862 [inline]
__schedule+0x87c/0x1ed0 kernel/sched/core.c:3504
schedule+0xfb/0x450 kernel/sched/core.c:3548
schedule_preempt_disabled+0x10/0x20 kernel/sched/core.c:3606
__mutex_lock_common kernel/locking/mutex.c:834 [inline]
__mutex_lock+0xede/0x1820 kernel/locking/mutex.c:894
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:909
commit_echoes+0x13f/0x1d0 drivers/tty/n_tty.c:762
n_tty_receive_char_fast drivers/tty/n_tty.c:1416 [inline]
n_tty_receive_buf_fast drivers/tty/n_tty.c:1576 [inline]
__receive_buf drivers/tty/n_tty.c:1611 [inline]
n_tty_receive_buf_common+0x205b/0x2c60 drivers/tty/n_tty.c:1709
n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1744
tty_ldisc_receive_buf+0xb0/0x190 drivers/tty/tty_buffer.c:456
tty_port_default_receive_buf+0x115/0x180 drivers/tty/tty_port.c:38
receive_buf drivers/tty/tty_buffer.c:475 [inline]
flush_to_ldisc+0x3fd/0x570 drivers/tty/tty_buffer.c:524
process_one_work+0xc73/0x1ba0 kernel/workqueue.c:2153
worker_thread+0x189/0x13c0 kernel/workqueue.c:2296
kthread+0x345/0x410 kernel/kthread.c:240
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412

Showing all locks held in the system:
1 lock held by khungtaskd/900:
#0: 000000009a22672f (rcu_read_lock){....}, at:
debug_show_all_locks+0xd0/0x428 kernel/locking/lockdep.c:4461
1 lock held by rsyslogd/4406:
2 locks held by getty/4496:
#0: 00000000e3ef92f1 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 0000000001a36f13 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2131
INFO: rcu_sched self-detected stall on CPU
INFO: rcu_sched detected stalls on CPUs/tasks:
0-....: (125001 ticks this GP) idle=e5a/1/4611686018427387906
softirq=174726/174726 fqs=31118

0-....: (125001 ticks this GP) idle=e5a/1/4611686018427387906
softirq=174726/174726 fqs=31118

(t=125010 jiffies g=86419 c=86418 q=678)
(detected by 1, t=125010 jiffies, g=86419, c=86418, q=678)
NMI backtrace for cpu 0
CPU: 0 PID: 30250 Comm: syz-executor5 Not tainted 4.18.0-rc2+ #124
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1c9/0x2b4 lib/dump_stack.c:113
nmi_cpu_backtrace.cold.4+0x19/0xce lib/nmi_backtrace.c:103
nmi_trigger_cpumask_backtrace+0x151/0x192 lib/nmi_backtrace.c:62
arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
trigger_single_cpu_backtrace include/linux/nmi.h:156 [inline]
rcu_dump_cpu_stacks+0x175/0x1c2 kernel/rcu/tree.c:1336
print_cpu_stall kernel/rcu/tree.c:1485 [inline]
check_cpu_stall.isra.60.cold.78+0x36c/0x5a6 kernel/rcu/tree.c:1553
__rcu_pending kernel/rcu/tree.c:3244 [inline]
rcu_pending kernel/rcu/tree.c:3291 [inline]
rcu_check_callbacks+0x23f/0xcd0 kernel/rcu/tree.c:2646
update_process_times+0x2d/0x70 kernel/time/timer.c:1636
tick_sched_handle+0x9f/0x180 kernel/time/tick-sched.c:164
tick_sched_timer+0x45/0x130 kernel/time/tick-sched.c:1274
__run_hrtimer kernel/time/hrtimer.c:1398 [inline]
__hrtimer_run_queues+0x3eb/0x10c0 kernel/time/hrtimer.c:1460
hrtimer_interrupt+0x2f3/0x750 kernel/time/hrtimer.c:1518
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline]
smp_apic_timer_interrupt+0x165/0x730 arch/x86/kernel/apic/apic.c:1050
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:863
</IRQ>
RIP: 0010:__read_once_size include/linux/compiler.h:188 [inline]
RIP: 0010:__sanitizer_cov_trace_pc+0x3b/0x50 kernel/kcov.c:106
Code: 48 89 e5 81 e2 00 01 1f 00 48 8b 75 08 75 2b 8b 90 90 12 00 00 83 fa
02 75 20 48 8b 88 98 12 00 00 8b 80 94 12 00 00 48 8b 11 <48> 83 c2 01 48
39 d0 76 07 48 89 34 d1 48 89 11 5d c3 0f 1f 00 55
RSP: 0018:ffff880196d677b0 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: 0000000000040000 RBX: 000000026e136b20 RCX: ffffc9000ac73000
RDX: 000000000003ffff RSI: ffffffff83a45704 RDI: 0000000000000001
RBP: ffff880196d677b0 R08: ffff8801caf0a0c0 R09: 0000000000000006
R10: ffff8801caf0a0c0 R11: 0000000000000000 R12: ffffc90013387000
R13: 0000000000000771 R14: 000000026e136b20 R15: 0000000000000000
__process_echoes+0x264/0x8d0 drivers/tty/n_tty.c:731
flush_echoes drivers/tty/n_tty.c:799 [inline]
__receive_buf drivers/tty/n_tty.c:1615 [inline]
n_tty_receive_buf_common+0x11dd/0x2c60 drivers/tty/n_tty.c:1709
n_tty_receive_buf+0x30/0x40 drivers/tty/n_tty.c:1738
tiocsti drivers/tty/tty_io.c:2180 [inline]
tty_ioctl+0x7e7/0x1870 drivers/tty/tty_io.c:2566
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x1de/0x1720 fs/ioctl.c:684
ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
__do_sys_ioctl fs/ioctl.c:708 [inline]
__se_sys_ioctl fs/ioctl.c:706 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455a99
Code: 1d ba 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 eb b9 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f0a65cc3c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f0a65cc46d4 RCX: 0000000000455a99
RDX: 0000000020000000 RSI: 0000000000005412 RDI: 0000000000000016
RBP: 000000000072bff0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004be97b R14: 00000000004cd6c8 R15: 0000000000000002
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 30250 Comm: syz-executor5 Not tainted 4.18.0-rc2+ #124
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:rep_nop arch/x86/include/asm/processor.h:658 [inline]
RIP: 0010:cpu_relax arch/x86/include/asm/processor.h:663 [inline]
RIP: 0010:virt_spin_lock arch/x86/include/asm/qspinlock.h:66 [inline]
RIP: 0010:native_queued_spin_lock_slowpath+0x250/0x1200
kernel/locking/qspinlock.c:305
Code: f3 48 ab 48 8b 45 d0 65 48 33 04 25 28 00 00 00 0f 85 cc 0d 00 00 48
81 c4 08 04 00 00 5b 41 5c 41 5d 41 5e 41 5f 5d c3 f3 90 <e9> 27 ff ff ff
8b 83 40 fc ff ff 3d 00 01 00 00 0f 84 12 04 00 00
RSP: 0018:ffff8801dae06f50 EFLAGS: 00000002
RAX: 0000000000000000 RBX: ffff8801dae07358 RCX: ffffffff815fa399
RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffffffff88f95a80
RBP: ffff8801dae07380 R08: fffffbfff11f2b51 R09: fffffbfff11f2b50
R10: fffffbfff11f2b50 R11: ffffffff88f95a83 R12: ffffed003b5c0e4b
R13: 0000000000000001 R14: dffffc0000000000 R15: ffffffff88f95a80
FS: 00007f0a65cc4700(0000) GS:ffff8801dae00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f26f4e49518 CR3: 0000000195c05000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:674 [inline]
queued_spin_lock_slowpath arch/x86/include/asm/qspinlock.h:32 [inline]
queued_spin_lock include/asm-generic/qspinlock.h:88 [inline]
do_raw_spin_lock+0x1a7/0x200 kernel/locking/spinlock_debug.c:113
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:117 [inline]
_raw_spin_lock_irqsave+0x9e/0xc0 kernel/locking/spinlock.c:152
print_cpu_stall kernel/rcu/tree.c:1487 [inline]
check_cpu_stall.isra.60.cold.78+0x374/0x5a6 kernel/rcu/tree.c:1553
__rcu_pending kernel/rcu/tree.c:3244 [inline]
rcu_pending kernel/rcu/tree.c:3291 [inline]
rcu_check_callbacks+0x23f/0xcd0 kernel/rcu/tree.c:2646
update_process_times+0x2d/0x70 kernel/time/timer.c:1636
tick_sched_handle+0x9f/0x180 kernel/time/tick-sched.c:164
tick_sched_timer+0x45/0x130 kernel/time/tick-sched.c:1274
__run_hrtimer kernel/time/hrtimer.c:1398 [inline]
__hrtimer_run_queues+0x3eb/0x10c0 kernel/time/hrtimer.c:1460
hrtimer_interrupt+0x2f3/0x750 kernel/time/hrtimer.c:1518
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline]
smp_apic_timer_interrupt+0x165/0x730 arch/x86/kernel/apic/apic.c:1050
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:863
</IRQ>
RIP: 0010:__read_once_size include/linux/compiler.h:188 [inline]
RIP: 0010:__sanitizer_cov_trace_pc+0x3b/0x50 kernel/kcov.c:106
Code: 48 89 e5 81 e2 00 01 1f 00 48 8b 75 08 75 2b 8b 90 90 12 00 00 83 fa
02 75 20 48 8b 88 98 12 00 00 8b 80 94 12 00 00 48 8b 11 <48> 83 c2 01 48
39 d0 76 07 48 89 34 d1 48 89 11 5d c3 0f 1f 00 55
RSP: 0018:ffff880196d677b0 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: 0000000000040000 RBX: 000000026e136b20 RCX: ffffc9000ac73000
RDX: 000000000003ffff RSI: ffffffff83a45704 RDI: 0000000000000001
RBP: ffff880196d677b0 R08: ffff8801caf0a0c0 R09: 0000000000000006
R10: ffff8801caf0a0c0 R11: 0000000000000000 R12: ffffc90013387000
R13: 0000000000000771 R14: 000000026e136b20 R15: 0000000000000000
__process_echoes+0x264/0x8d0 drivers/tty/n_tty.c:731
flush_echoes drivers/tty/n_tty.c:799 [inline]
__receive_buf drivers/tty/n_tty.c:1615 [inline]
n_tty_receive_buf_common+0x11dd/0x2c60 drivers/tty/n_tty.c:1709
n_tty_receive_buf+0x30/0x40 drivers/tty/n_tty.c:1738
tiocsti drivers/tty/tty_io.c:2180 [inline]
tty_ioctl+0x7e7/0x1870 drivers/tty/tty_io.c:2566
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x1de/0x1720 fs/ioctl.c:684
ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
__do_sys_ioctl fs/ioctl.c:708 [inline]
__se_sys_ioctl fs/ioctl.c:706 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455a99
Code: 1d ba 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 eb b9 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f0a65cc3c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f0a65cc46d4 RCX: 0000000000455a99
RDX: 0000000020000000 RSI: 0000000000005412 RDI: 0000000000000016
RBP: 000000000072bff0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004be97b R14: 00000000004cd6c8 R15: 0000000000000002
2 locks held by getty/4497:
INFO: NMI handler (nmi_cpu_backtrace_handler) took too long to run: 1.525
msecs
#0: 00000000fc3ca002 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 000000000eea208c (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2131
2 locks held by getty/4498:
#0: 00000000023e5337 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 0000000011c80644 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2131
2 locks held by getty/4499:
#0: 00000000bb2f9348 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000ad24ab98 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2131
2 locks held by getty/4500:
#0: 000000000cb01976 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 0000000014167e60 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2131
2 locks held by getty/4501:
#0: 0000000079010c1e (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000e8ab401a (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2131
2 locks held by getty/4502:
#0: 000000008813ffdf (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000389fe4af (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2131
6 locks held by kworker/u4:7/28378:
#0: 0000000072dd80f5 ((wq_completion)"events_unbound"){+.+.}, at:
__write_once_size include/linux/compiler.h:215 [inline]
#0: 0000000072dd80f5 ((wq_completion)"events_unbound"){+.+.}, at:
arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
#0: 0000000072dd80f5 ((wq_completion)"events_unbound"){+.+.}, at:
atomic64_set include/asm-generic/atomic-instrumented.h:40 [inline]
#0: 0000000072dd80f5 ((wq_completion)"events_unbound"){+.+.}, at:
atomic_long_set include/asm-generic/atomic-long.h:59 [inline]
#0: 0000000072dd80f5 ((wq_completion)"events_unbound"){+.+.}, at:
set_work_data kernel/workqueue.c:617 [inline]
#0: 0000000072dd80f5 ((wq_completion)"events_unbound"){+.+.}, at:
set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
#0: 0000000072dd80f5 ((wq_completion)"events_unbound"){+.+.}, at:
process_one_work+0xb44/0x1ba0 kernel/workqueue.c:2124
#1: 00000000ec69bcf0 ((work_completion)(&buf->work)){+.+.}, at:
process_one_work+0xb9b/0x1ba0 kernel/workqueue.c:2128
#2: 0000000048ca8f2f (&port->buf.lock/1){+.+.}, at:
flush_to_ldisc+0xbf/0x570 drivers/tty/tty_buffer.c:496
#3: 0000000030e79f75 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref+0x22/0x90
drivers/tty/tty_ldisc.c:284
#4: 0000000039e19c75 (&o_tty->termios_rwsem/1){++++}, at:
n_tty_receive_buf_common+0xeb/0x2c60 drivers/tty/n_tty.c:1672
#5: 000000008cbcd005 (&ldata->output_lock){+.+.}, at:
commit_echoes+0x13f/0x1d0 drivers/tty/n_tty.c:762
3 locks held by syz-executor5/30250:

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

NMI backtrace for cpu 1
CPU: 1 PID: 900 Comm: khungtaskd Not tainted 4.18.0-rc2+ #124
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+0x1c9/0x2b4 lib/dump_stack.c:113
nmi_cpu_backtrace.cold.4+0x19/0xce lib/nmi_backtrace.c:103
nmi_trigger_cpumask_backtrace+0x151/0x192 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:138 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:196 [inline]
watchdog+0x9c4/0xf80 kernel/hung_task.c:252
kthread+0x345/0x410 kernel/kthread.c:240
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 30250 Comm: syz-executor5 Not tainted 4.18.0-rc2+ #124
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:get_current arch/x86/include/asm/current.h:15 [inline]
RIP: 0010:write_comp_data+0xa/0x70 kernel/kcov.c:121
Code: e8 db d4 3d 00 e9 ad fc ff ff 4c 89 ef e8 2e d4 3d 00 e9 76 fc ff ff
e8 74 27 cb ff 90 90 90 90 55 65 4c 8b 04 25 40 ee 01 00 <65> 8b 05 bf e1
85 7e 48 89 e5 a9 00 01 1f 00 75 51 41 8b 80 90 12
RSP: 0018:ffff880196d677a0 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 0000000271a74952 RCX: ffffffff83a4577c
RDX: 0000000000000000 RSI: 00000000000000ff RDI: 0000000000000001
RBP: ffff880196d677b0 R08: ffff8801caf0a0c0 R09: 0000000000000006
R10: ffff8801caf0a0c0 R11: 0000000000000000 R12: ffffc90013387000
R13: 0000000000000771 R14: 0000000271a74953 R15: 0000000000000000
FS: 00007f0a65cc4700(0000) GS:ffff8801dae00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f26f4e49518 CR3: 0000000195c05000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
__process_echoes+0x2dc/0x8d0 drivers/tty/n_tty.c:732
flush_echoes drivers/tty/n_tty.c:799 [inline]
__receive_buf drivers/tty/n_tty.c:1615 [inline]
n_tty_receive_buf_common+0x11dd/0x2c60 drivers/tty/n_tty.c:1709
n_tty_receive_buf+0x30/0x40 drivers/tty/n_tty.c:1738
tiocsti drivers/tty/tty_io.c:2180 [inline]
tty_ioctl+0x7e7/0x1870 drivers/tty/tty_io.c:2566
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x1de/0x1720 fs/ioctl.c:684
ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
__do_sys_ioctl fs/ioctl.c:708 [inline]
__se_sys_ioctl fs/ioctl.c:706 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455a99
Code: 1d ba 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 eb b9 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f0a65cc3c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f0a65cc46d4 RCX: 0000000000455a99
RDX: 0000000020000000 RSI: 0000000000005412 RDI: 0000000000000016
RBP: 000000000072bff0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004be97b R14: 00000000004cd6c8 R15: 0000000000000002


---
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[syzbot]

> This is a dup of "INFO: rcu detected stall in __process_echoes" which was
> already fixed in linux.git#master before syzbot sent this report.

> #syz fix: n_tty: Access echo_* variables carefully.

Your 'fix:' command is accepted, but please keep
syzkaller-upst...@googlegroups.com mailing list in CC next
time. It serves as a history of what happened with each bug report. Thank
you.