[v5.15] INFO: task hung in vt_ioctl

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: aabd761612db Linux 5.15.215
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1774ca9e580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f161cbc9aef65db0
dashboard link: https://syzkaller.appspot.com/bug?extid=3e4cfd6db5f42b0e1a62
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f636f56d3662/disk-aabd7616.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f1a46620f40c/vmlinux-aabd7616.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9b78bb48b022/bzImage-aabd7616.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3e4cfd...@syzkaller.appspotmail.com

INFO: task syz.0.187:5041 blocked for more than 144 seconds.
Tainted: G S syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.187 state:D stack:26704 pid: 5041 ppid: 4187 flags:0x00004004
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5049 [inline]
__schedule+0x11c3/0x4350 kernel/sched/core.c:6395
schedule+0x11b/0x1e0 kernel/sched/core.c:6478
schedule_timeout+0xbd/0x2d0 kernel/time/timer.c:2093
__down_common+0x289/0x3b0 kernel/locking/semaphore.c:228
down+0x7e/0xd0 kernel/locking/semaphore.c:63
console_lock+0x29/0x70 kernel/printk/printk.c:2557
vt_k_ioctl drivers/tty/vt/vt_ioctl.c:380 [inline]
vt_ioctl+0x6ff/0x1cb0 drivers/tty/vt/vt_ioctl.c:752
tty_ioctl+0x848/0xc30 drivers/tty/tty_io.c:2810
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fa22a07c0d9
RSP: 002b:00007fa2282d4028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fa22a303fa0 RCX: 00007fa22a07c0d9
RDX: 0000000000000001 RSI: 0000000000004b3a RDI: 0000000000000004
RBP: 00007fa22a113024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa22a304038 R14: 00007fa22a303fa0 R15: 00007ffc714e0358
</TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/27:
#0: ffffffff8c31ef60 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x0/0x30
2 locks held by getty/3948:
#0: ffff88814d613098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x21/0x70 drivers/tty/tty_ldisc.c:252
#1: ffffc900026562e8 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x594/0x1a50 drivers/tty/n_tty.c:2158
3 locks held by kworker/u4:7/4298:
1 lock held by syz.4.181/5021:
4 locks held by syz.3.210/5150:
#0: ffff888079130870 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2bf/0x370 fs/file.c:1056
#1: ffff88801bc3a460 (sb_writers#8){.+.+}-{0:0}, at: vfs_write+0x296/0xd70 fs/read_write.c:590
#2: ffff888060b74888 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x1dc/0x500 fs/kernfs/file.c:287
#3: ffff888147a68bd0 (kn->active#524){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x1fd/0x500 fs/kernfs/file.c:288
4 locks held by syz.9.333/5777:
#0: ffff88802b66a098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x21/0x70 drivers/tty/tty_ldisc.c:252
#1: ffff88802b66a130 (&tty->atomic_write_lock){+.+.}-{3:3}, at: tty_write_lock drivers/tty/tty_io.c:961 [inline]
#1: ffff88802b66a130 (&tty->atomic_write_lock){+.+.}-{3:3}, at: do_tty_write drivers/tty/tty_io.c:984 [inline]
#1: ffff88802b66a130 (&tty->atomic_write_lock){+.+.}-{3:3}, at: file_tty_write+0x23c/0x8a0 drivers/tty/tty_io.c:1110
#2: ffff88802b66a2e8 (&tty->termios_rwsem){++++}-{3:3}, at: n_tty_write+0x1ec/0x1220 drivers/tty/n_tty.c:2322
#3: ffffc90001111378 (&ldata->output_lock){+.+.}-{3:3}, at: process_output_block drivers/tty/n_tty.c:547 [inline]
#3: ffffc90001111378 (&ldata->output_lock){+.+.}-{3:3}, at: n_tty_write+0x66a/0x1220 drivers/tty/n_tty.c:2339
2 locks held by syz.2.345/5825:
#0: ffffffff8c9f62e8 (tty_mutex){+.+.}-{3:3}, at: tty_open_by_driver drivers/tty/tty_io.c:2064 [inline]
#0: ffffffff8c9f62e8 (tty_mutex){+.+.}-{3:3}, at: tty_open+0x20a/0xcd0 drivers/tty/tty_io.c:2148
#1: ffff88801d6291c0 (&tty->legacy_mutex){+.+.}-{3:3}, at: tty_init_dev+0x6f/0x470 drivers/tty/tty_io.c:1430
1 lock held by syz.0.396/6187:
#0: ffffffff8c9f62e8 (tty_mutex){+.+.}-{3:3}, at: tty_open_by_driver drivers/tty/tty_io.c:2064 [inline]
#0: ffffffff8c9f62e8 (tty_mutex){+.+.}-{3:3}, at: tty_open+0x20a/0xcd0 drivers/tty/tty_io.c:2148
1 lock held by syz.6.400/6212:
#0: ffffffff8c9f62e8 (tty_mutex){+.+.}-{3:3}, at: tty_open_by_driver drivers/tty/tty_io.c:2064 [inline]
#0: ffffffff8c9f62e8 (tty_mutex){+.+.}-{3:3}, at: tty_open+0x20a/0xcd0 drivers/tty/tty_io.c:2148
1 lock held by syz.3.412/6259:
#0: ffffffff8c9f62e8 (tty_mutex){+.+.}-{3:3}, at: tty_open_by_driver drivers/tty/tty_io.c:2064 [inline]
#0: ffffffff8c9f62e8 (tty_mutex){+.+.}-{3:3}, at: tty_open+0x20a/0xcd0 drivers/tty/tty_io.c:2148
1 lock held by syz.4.435/6448:
#0: ffffffff8c9f62e8 (tty_mutex){+.+.}-{3:3}, at: tty_open_by_driver drivers/tty/tty_io.c:2064 [inline]
#0: ffffffff8c9f62e8 (tty_mutex){+.+.}-{3:3}, at: tty_open+0x20a/0xcd0 drivers/tty/tty_io.c:2148
3 locks held by kworker/0:23/6630:
3 locks held by syz.8.453/6660:
1 lock held by syz.7.455/6667:
#0: ffffffff8c9f62e8 (tty_mutex){+.+.}-{3:3}, at: tty_open_by_driver drivers/tty/tty_io.c:2064 [inline]
#0: ffffffff8c9f62e8 (tty_mutex){+.+.}-{3:3}, at: tty_open+0x20a/0xcd0 drivers/tty/tty_io.c:2148
2 locks held by sed/6675:

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

NMI backtrace for cpu 0
CPU: 0 PID: 27 Comm: khungtaskd Tainted: G S syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
<TASK>
dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
nmi_cpu_backtrace+0x3a2/0x3d0 lib/nmi_backtrace.c:111
nmi_trigger_cpumask_backtrace+0x163/0x280 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:148 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:212 [inline]
watchdog+0xe1b/0xe60 kernel/hung_task.c:369
kthread+0x42e/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
</TASK>


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