======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
kworker/0:17/4583 is trying to acquire lock:
ffff8880176280b8 (&buf->lock){+.+.}-{3:3}, at: tty_buffer_flush+0x78/0x3e0 drivers/tty/tty_buffer.c:230

but task is already holding lock:
ffffffff8cb21e20 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x24/0x210 drivers/tty/vt/vt_ioctl.c:985

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (console_lock){+.+.}-{0:0}:
       console_lock+0x160/0x1c0 kernel/printk/printk.c:2629
       con_flush_chars+0x47/0x270 drivers/tty/vt/vt.c:3365
       __receive_buf drivers/tty/n_tty.c:1627 [inline]
       n_tty_receive_buf_common+0xe0d/0x1470 drivers/tty/n_tty.c:1721
       tty_port_default_receive_buf+0x69/0x90 drivers/tty/tty_port.c:39
       receive_buf drivers/tty/tty_buffer.c:515 [inline]
       flush_to_ldisc+0x2b9/0x800 drivers/tty/tty_buffer.c:565
       process_one_work+0x8ab/0x1160 kernel/workqueue.c:2292
       worker_thread+0xaf5/0x12a0 kernel/workqueue.c:2439
       kthread+0x29d/0x330 kernel/kthread.c:376
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

-> #1 (&tty->termios_rwsem){++++}-{3:3}:
       down_read+0x42/0x2d0 kernel/locking/rwsem.c:1520
       n_tty_receive_buf_common+0x79/0x1470 drivers/tty/n_tty.c:1684
       tty_port_default_receive_buf+0x69/0x90 drivers/tty/tty_port.c:39
       receive_buf drivers/tty/tty_buffer.c:515 [inline]
       flush_to_ldisc+0x2b9/0x800 drivers/tty/tty_buffer.c:565
       process_one_work+0x8ab/0x1160 kernel/workqueue.c:2292
       worker_thread+0xaf5/0x12a0 kernel/workqueue.c:2439
       kthread+0x29d/0x330 kernel/kthread.c:376
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

-> #0 (&buf->lock){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3095 [inline]
       check_prevs_add kernel/locking/lockdep.c:3214 [inline]
       validate_chain kernel/locking/lockdep.c:3830 [inline]
       __lock_acquire+0x2d18/0x7c40 kernel/locking/lockdep.c:5063
       lock_acquire+0x1bb/0x4a0 kernel/locking/lockdep.c:5676
       __mutex_lock_common kernel/locking/mutex.c:603 [inline]
       __mutex_lock+0x12d/0xae0 kernel/locking/mutex.c:747
       tty_buffer_flush+0x78/0x3e0 drivers/tty/tty_buffer.c:230
       tty_ldisc_flush+0x6a/0xc0 drivers/tty/tty_ldisc.c:389
       __do_SAK+0x25c/0x630 drivers/tty/tty_io.c:3011
       vc_SAK+0x74/0x210 drivers/tty/vt/vt_ioctl.c:995
       process_one_work+0x8ab/0x1160 kernel/workqueue.c:2292
       worker_thread+0xaf5/0x12a0 kernel/workqueue.c:2439
       kthread+0x29d/0x330 kernel/kthread.c:376
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

other info that might help us debug this:

Chain exists of:
  &buf->lock --> &tty->termios_rwsem --> console_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(console_lock);
                               lock(&tty->termios_rwsem);
                               lock(console_lock);
  lock(&buf->lock);

 *** DEADLOCK ***

4 locks held by kworker/0:17/4583:
 #0: ffff888017470938 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x7b4/0x1160 kernel/workqueue.c:2267
 #1: ffffc900052e7d00 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_one_work+0x7b4/0x1160 kernel/workqueue.c:2267
 #2: ffffffff8cb21e20 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x24/0x210 drivers/tty/vt/vt_ioctl.c:985
 #3: ffff888057ee4098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref drivers/tty/tty_ldisc.c:264 [inline]
 #3: ffff888057ee4098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_flush+0x1c/0xc0 drivers/tty/tty_ldisc.c:387

stack backtrace:
CPU: 0 PID: 4583 Comm: kworker/0:17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: events vc_SAK
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x24e lib/dump_stack.c:106
 check_noncircular+0x296/0x330 kernel/locking/lockdep.c:2170
 check_prev_add kernel/locking/lockdep.c:3095 [inline]
 check_prevs_add kernel/locking/lockdep.c:3214 [inline]
 validate_chain kernel/locking/lockdep.c:3830 [inline]
 __lock_acquire+0x2d18/0x7c40 kernel/locking/lockdep.c:5063
 lock_acquire+0x1bb/0x4a0 kernel/locking/lockdep.c:5676
 __mutex_lock_common kernel/locking/mutex.c:603 [inline]
 __mutex_lock+0x12d/0xae0 kernel/locking/mutex.c:747
 tty_buffer_flush+0x78/0x3e0 drivers/tty/tty_buffer.c:230
 tty_ldisc_flush+0x6a/0xc0 drivers/tty/tty_ldisc.c:389
 __do_SAK+0x25c/0x630 drivers/tty/tty_io.c:3011
 vc_SAK+0x74/0x210 drivers/tty/vt/vt_ioctl.c:995
 process_one_work+0x8ab/0x1160 kernel/workqueue.c:2292
 worker_thread+0xaf5/0x12a0 kernel/workqueue.c:2439
 kthread+0x29d/0x330 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>