INFO: task hung in tty_set_termios

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
c2a9838452a4d71f76103c18c926468a9ea05713 (Fri Mar 30 05:27:12 2018 +0000)
Merge tag 'for-4.16/dm-fixes-4' of
git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm
syzbot dashboard link:
https://syzkaller.appspot.com/bug?extid=adcaec3db47dacacf451

Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:
https://syzkaller.appspot.com/x/log.txt?id=4688830217060352
Kernel config:
https://syzkaller.appspot.com/x/.config?id=-8440362230543204781
compiler: gcc (GCC) 7.1.1 20170620
CC: [gre...@linuxfoundation.org jsl...@suse.com
linux-...@vger.kernel.org]

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+adcaec...@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for
details.
If you forward the report, please keep this part and the footer.

INFO: task syz-executor0:14547 blocked for more than 120 seconds.
Not tainted 4.16.0-rc7+ #6
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0 D24696 14547 4431 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2862 [inline]
__schedule+0x8fb/0x1ec0 kernel/sched/core.c:3440
schedule+0xf5/0x430 kernel/sched/core.c:3499
__rwsem_down_write_failed_common+0x7c0/0x1540
kernel/locking/rwsem-xadd.c:566
rwsem_down_write_failed+0xe/0x10 kernel/locking/rwsem-xadd.c:595
call_rwsem_down_write_failed+0x17/0x30 arch/x86/lib/rwsem.S:117
__down_write arch/x86/include/asm/rwsem.h:142 [inline]
down_write+0xa2/0x120 kernel/locking/rwsem.c:72
tty_set_termios+0xe5/0xa60 drivers/tty/tty_ioctl.c:328
set_termios+0x392/0x6d0 drivers/tty/tty_ioctl.c:414
tty_mode_ioctl+0x9fc/0xb30 drivers/tty/tty_ioctl.c:749
n_tty_ioctl_helper+0x40/0x360 drivers/tty/tty_ioctl.c:940
n_tty_ioctl+0x14d/0x2d0 drivers/tty/n_tty.c:2441
tty_ioctl+0x336/0x1610 drivers/tty/tty_io.c:2655
vfs_ioctl fs/ioctl.c:46 [inline]
do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4548b9
RSP: 002b:00007f537ed6cc68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f537ed6d6d4 RCX: 00000000004548b9
RDX: 0000000020000140 RSI: 0000000000005402 RDI: 0000000000000015
RBP: 000000000072bf58 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000002f9 R14: 00000000006f67f8 R15: 0000000000000001

Showing all locks held in the system:
2 locks held by khungtaskd/868:
#0: (rcu_read_lock){....}, at: [<00000000b945f5c3>]
check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
#0: (rcu_read_lock){....}, at: [<00000000b945f5c3>] watchdog+0x1c5/0xd60
kernel/hung_task.c:249
#1: (tasklist_lock){.+.+}, at: [<000000004f3eb2e0>]
debug_show_all_locks+0xd3/0x3d0 kernel/locking/lockdep.c:4470
2 locks held by getty/4358:
#0: (&tty->ldisc_sem){++++}, at: [<00000000ffde600d>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000002718afc6>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4359:
#0: (&tty->ldisc_sem){++++}, at: [<00000000ffde600d>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000002718afc6>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4360:
#0: (&tty->ldisc_sem){++++}, at: [<00000000ffde600d>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000002718afc6>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4361:
#0: (&tty->ldisc_sem){++++}, at: [<00000000ffde600d>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000002718afc6>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4362:
#0: (&tty->ldisc_sem){++++}, at: [<00000000ffde600d>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000002718afc6>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4363:
#0: (&tty->ldisc_sem){++++}, at: [<00000000ffde600d>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000002718afc6>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4364:
#0: (&tty->ldisc_sem){++++}, at: [<00000000ffde600d>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000002718afc6>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by syz-executor0/14547:
#0: (&tty->ldisc_sem){++++}, at: [<00000000ffde600d>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (&o_tty->termios_rwsem/1){++++}, at: [<000000008247af10>]
tty_set_termios+0xe5/0xa60 drivers/tty/tty_ioctl.c:328
1 lock held by syz-executor1/14545:
#0: (event_mutex){+.+.}, at: [<000000009aaa04ba>]
perf_trace_destroy+0x28/0x100 kernel/trace/trace_event_perf.c:234
3 locks held by syz-executor6/14579:
#0: (&sig->cred_guard_mutex){+.+.}, at: [<000000004a34bd2f>]
SYSC_perf_event_open+0x12ca/0x2e00 kernel/events/core.c:9990
#1: (&pmus_srcu){....}, at: [<0000000054b313f9>]
perf_event_alloc+0xf55/0x2b00 kernel/events/core.c:9551
#2: (event_mutex){+.+.}, at: [<0000000088baf472>]
perf_trace_init+0x58/0xab0 kernel/trace/trace_event_perf.c:216
1 lock held by syz-executor5/14549:
#0: (&type->s_umount_key#28){++++}, at: [<0000000015cce8cc>] SYSC_syncfs
fs/sync.c:165 [inline]
#0: (&type->s_umount_key#28){++++}, at: [<0000000015cce8cc>]
SyS_syncfs+0x86/0xe0 fs/sync.c:155
1 lock held by syz-executor5/14552:
#0: (&type->s_umount_key#28){++++}, at: [<000000003f27d1e3>]
iterate_supers+0xe1/0x250 fs/super.c:596
1 lock held by syz-executor5/14563:
#0: (&type->s_umount_key#28){++++}, at: [<0000000015cce8cc>] SYSC_syncfs
fs/sync.c:165 [inline]
#0: (&type->s_umount_key#28){++++}, at: [<0000000015cce8cc>]
SyS_syncfs+0x86/0xe0 fs/sync.c:155
1 lock held by syz-executor5/14564:
#0: (&type->s_umount_key#28){++++}, at: [<00000000a3899c5a>]
thaw_super+0x2c/0x260 fs/super.c:1499
3 locks held by syz-executor4/14559:
#0: (&sig->cred_guard_mutex){+.+.}, at: [<000000004a34bd2f>]
SYSC_perf_event_open+0x12ca/0x2e00 kernel/events/core.c:9990
#1: (&pmus_srcu){....}, at: [<0000000054b313f9>]
perf_event_alloc+0xf55/0x2b00 kernel/events/core.c:9551
#2: (event_mutex){+.+.}, at: [<0000000088baf472>]
perf_trace_init+0x58/0xab0 kernel/trace/trace_event_perf.c:216
1 lock held by syz-executor2/14562:
#0: (lock#6){+.+.}, at: [<00000000c6fcc0be>] lru_add_drain_all+0xb2/0x540
mm/swap.c:683
1 lock held by syz-executor7/14582:
#0: (&vcpu->mutex){+.+.}, at: [<00000000b1f9d6b0>]
kvm_vcpu_ioctl+0x1d1/0xff0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2542

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

NMI backtrace for cpu 1
CPU: 1 PID: 868 Comm: khungtaskd Not tainted 4.16.0-rc7+ #6
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x194/0x24d lib/dump_stack.c:53
nmi_cpu_backtrace+0x1d2/0x210 lib/nmi_backtrace.c:103
nmi_trigger_cpumask_backtrace+0x123/0x180 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_task kernel/hung_task.c:132 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:190 [inline]
watchdog+0x90c/0xd60 kernel/hung_task.c:249
kthread+0x33c/0x400 kernel/kthread.c:238
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:406
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 5 Comm: kworker/u4:0 Not tainted 4.16.0-rc7+ #6
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: events_unbound flush_to_ldisc
RIP: 0010:__sanitizer_cov_trace_pc+0xd/0x50 kernel/kcov.c:94
RSP: 0018:ffff8801d9acf068 EFLAGS: 00000217
RAX: ffff8801d9abc140 RBX: ffffc90004f3c000 RCX: ffffffff82f384b2
RDX: 0000000000000004 RSI: 1ffff1003b357954 RDI: ffffc90004f3d4b4
RBP: ffff8801d9acf068 R08: 1ffff1003b359db5 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 00000005e23f7253
R13: dffffc0000000000 R14: 0000000000000254 R15: 0000000000001a37
FS: 0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f537ed2adb8 CR3: 0000000007a22004 CR4: 00000000001626f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
__process_echoes+0x648/0x770 drivers/tty/n_tty.c:736
commit_echoes+0x147/0x1b0 drivers/tty/n_tty.c:764
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+0x1156/0x2520 drivers/tty/n_tty.c:1709
n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1744
tty_ldisc_receive_buf+0xa7/0x180 drivers/tty/tty_buffer.c:456
tty_port_default_receive_buf+0x106/0x160 drivers/tty/tty_port.c:38
receive_buf drivers/tty/tty_buffer.c:475 [inline]
flush_to_ldisc+0x3c4/0x590 drivers/tty/tty_buffer.c:524
process_one_work+0xc47/0x1bb0 kernel/workqueue.c:2113
worker_thread+0x223/0x1990 kernel/workqueue.c:2247
kthread+0x33c/0x400 kernel/kthread.c:238
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:406
Code: ff 48 8b bd d0 fe ff ff e8 61 47 38 00 e9 c3 fc ff ff 90 90 90 90 90
90 90 90 90 90 90 90 55 65 48 8b 04 25 c0 ed 01 00 48 89 e5 <65> 8b 15 1c
24 90 7e 81 e2 00 01 1f 00 48 8b 4d 08 75 2b 8b 90


---
This bug is generated by a dumb bot. It may contain errors.
See https://goo.gl/tpsmEJ for details.
Direct all questions to syzk...@googlegroups.com.

syzbot will keep track of this bug report.
If you forgot to add the Reported-by tag, once the fix for this bug is
merged
into any tree, please reply to this email with:
#syz fix: exact-commit-title
To mark this as a duplicate of another syzbot report, please reply with:
#syz dup: exact-subject-of-another-report
If it's a one-off invalid bug report, please reply with:
#syz invalid
Note: if the crash happens again, it will cause creation of a new bug
report.
Note: all commands must start from beginning of the line in the email body.
To upstream this report, please reply with:
#syz upstream