INFO: task hung in tty_ioctl

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: a06b0c82a049 Merge tag 'printk-for-4.19-rc4' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=171f5dae400000
kernel config: https://syzkaller.appspot.com/x/.config?x=b8f349d23d3c4835
dashboard link: https://syzkaller.appspot.com/bug?extid=dcb709d3f1aab5efa89d
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+dcb709...@syzkaller.appspotmail.com

IPv6: ADDRCONF(NETDEV_UP): veth0: link is not ready
IPv6: ADDRCONF(NETDEV_UP): veth1: link is not ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
8021q: adding VLAN 0 to HW filter on device team0
INFO: task syz-executor5:7776 blocked for more than 140 seconds.
Not tainted 4.19.0-rc3+ #236
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor5 D20520 7776 5356 0x00000000
Call Trace:
context_switch kernel/sched/core.c:2825 [inline]
__schedule+0x86c/0x1ed0 kernel/sched/core.c:3473
schedule+0xfe/0x460 kernel/sched/core.c:3517
schedule_timeout+0x1cc/0x260 kernel/time/timer.c:1780
down_read_failed drivers/tty/tty_ldsem.c:224 [inline]
__ldsem_down_read_nested+0x538/0xb80 drivers/tty/tty_ldsem.c:318
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
tty_ldisc_ref_wait+0x25/0x80 drivers/tty/tty_ldisc.c:263
tty_ioctl+0x512/0x1820 drivers/tty/tty_io.c:2650
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:501 [inline]
do_vfs_ioctl+0x1de/0x1720 fs/ioctl.c:685
ksys_ioctl+0xa9/0xd0 fs/ioctl.c:702
__do_sys_ioctl fs/ioctl.c:709 [inline]
__se_sys_ioctl fs/ioctl.c:707 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:707
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4572d9
Code: Bad RIP value.
RSP: 002b:00007fcb278c7c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fcb278c86d4 RCX: 00000000004572d9
RDX: 0000000020000100 RSI: 0000000000005600 RDI: 0000000000000005
RBP: 00000000009301e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004d2550 R14: 00000000004c7a92 R15: 0000000000000002

Showing all locks held in the system:
1 lock held by khungtaskd/984:
#0: 000000005b7728df (rcu_read_lock){....}, at:
debug_show_all_locks+0xd0/0x424 kernel/locking/lockdep.c:4436
1 lock held by rsyslogd/5220:
#0: 00000000a3a7bdf0 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x1bb/0x200
fs/file.c:766
2 locks held by getty/5310:
#0: 000000008e2207d8 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 000000009dcb0bff (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
2 locks held by getty/5311:
#0: 00000000270defab (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 0000000097dae4df (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
2 locks held by getty/5312:
#0: 0000000030f6ec08 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 000000005f629db3 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
2 locks held by getty/5313:
#0: 00000000606b13e2 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 000000002218fc4b (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
2 locks held by getty/5314:
#0: 000000001a34fff3 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 00000000ba317663 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
2 locks held by getty/5315:
#0: 00000000ae035bea (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 000000008c2895aa (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
2 locks held by getty/5316:
#0: 000000003a514108 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 000000004b54e2c8 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
2 locks held by syz-executor4/6918:
#0: 000000007ca4e0a5 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 000000002c7ee2c5 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
1 lock held by syz-executor5/7776:
#0: 00000000f25c1c8e (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
2 locks held by syz-executor5/7778:
#0: 00000000f25c1c8e (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 00000000b4b85db3 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
1 lock held by syz-executor4/8706:
#0: 00000000df707619 (sk_lock-AF_ALG){+.+.}, at: lock_sock
include/net/sock.h:1491 [inline]
#0: 00000000df707619 (sk_lock-AF_ALG){+.+.}, at: hash_sendmsg+0xd9/0xae0
crypto/algif_hash.c:81

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

NMI backtrace for cpu 1
CPU: 1 PID: 984 Comm: khungtaskd Not tainted 4.19.0-rc3+ #236
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+0x1c4/0x2b4 lib/dump_stack.c:113
nmi_cpu_backtrace.cold.3+0x63/0xa2 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x1b3/0x1ed 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:144 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:204 [inline]
watchdog+0xb3e/0x1050 kernel/hung_task.c:265
kthread+0x35a/0x420 kernel/kthread.c:246
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:413
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0x6/0x10
arch/x86/include/asm/irqflags.h:57


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.