======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
kworker/0:4/5811 is trying to acquire lock:
ffff8880186510b8 (&buf->lock){+.+.}-{3:3}, at: tty_buffer_flush+0x79/0x3e0 drivers/tty/tty_buffer.c:229

but task is already holding lock:
ffffffff8d126180 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x28/0x220 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+0x164/0x1b0 kernel/printk/printk.c:2686
       con_flush_chars+0x4b/0x280 drivers/tty/vt/vt.c:3315
       __receive_buf drivers/tty/n_tty.c:1650 [inline]
       n_tty_receive_buf_common+0xcdc/0x1380 drivers/tty/n_tty.c:1745
       tty_port_default_receive_buf+0x6e/0xa0 drivers/tty/tty_port.c:37
       receive_buf drivers/tty/tty_buffer.c:445 [inline]
       flush_to_ldisc+0x2bc/0x7f0 drivers/tty/tty_buffer.c:495
       process_one_work kernel/workqueue.c:2657 [inline]
       process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2734
       worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2815
       kthread+0x2fa/0x390 kernel/kthread.c:388
       ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
       ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293

-> #1 (&tty->termios_rwsem){++++}-{3:3}:
       down_read+0x46/0x2e0 kernel/locking/rwsem.c:1520
       n_tty_receive_buf_common+0x7d/0x1380 drivers/tty/n_tty.c:1708
       tty_port_default_receive_buf+0x6e/0xa0 drivers/tty/tty_port.c:37
       receive_buf drivers/tty/tty_buffer.c:445 [inline]
       flush_to_ldisc+0x2bc/0x7f0 drivers/tty/tty_buffer.c:495
       process_one_work kernel/workqueue.c:2657 [inline]
       process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2734
       worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2815
       kthread+0x2fa/0x390 kernel/kthread.c:388
       ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
       ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293

-> #0 (&buf->lock){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3134 [inline]
       check_prevs_add kernel/locking/lockdep.c:3253 [inline]
       validate_chain kernel/locking/lockdep.c:3869 [inline]
       __lock_acquire+0x37ef/0x7d80 kernel/locking/lockdep.c:5137
       lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5754
       __mutex_lock_common kernel/locking/mutex.c:603 [inline]
       __mutex_lock+0x135/0xc80 kernel/locking/mutex.c:747
       tty_buffer_flush+0x79/0x3e0 drivers/tty/tty_buffer.c:229
       tty_ldisc_flush+0x6b/0xc0 drivers/tty/tty_ldisc.c:388
       __do_SAK+0x25b/0x680 drivers/tty/tty_io.c:3014
       vc_SAK+0x78/0x220 drivers/tty/vt/vt_ioctl.c:995
       process_one_work kernel/workqueue.c:2657 [inline]
       process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2734
       worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2815
       kthread+0x2fa/0x390 kernel/kthread.c:388
       ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
       ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293

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/0:4/5811:
 #0: ffff888017c70938 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2632 [inline]
 #0: ffff888017c70938 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2734
 #1: ffffc9000489fd00 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2632 [inline]
 #1: ffffc9000489fd00 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2734
 #2: ffffffff8d126180 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x28/0x220 drivers/tty/vt/vt_ioctl.c:985
 #3: ffff8880301600a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref drivers/tty/tty_ldisc.c:263 [inline]
 #3: ffff8880301600a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_flush+0x20/0xc0 drivers/tty/tty_ldisc.c:386

stack backtrace:
CPU: 0 PID: 5811 Comm: kworker/0:4 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+0x18c/0x250 lib/dump_stack.c:106
 check_noncircular+0x2fc/0x400 kernel/locking/lockdep.c:2187
 check_prev_add kernel/locking/lockdep.c:3134 [inline]
 check_prevs_add kernel/locking/lockdep.c:3253 [inline]
 validate_chain kernel/locking/lockdep.c:3869 [inline]
 __lock_acquire+0x37ef/0x7d80 kernel/locking/lockdep.c:5137
 lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5754
 __mutex_lock_common kernel/locking/mutex.c:603 [inline]
 __mutex_lock+0x135/0xc80 kernel/locking/mutex.c:747
 tty_buffer_flush+0x79/0x3e0 drivers/tty/tty_buffer.c:229
 tty_ldisc_flush+0x6b/0xc0 drivers/tty/tty_ldisc.c:388
 __do_SAK+0x25b/0x680 drivers/tty/tty_io.c:3014
 vc_SAK+0x78/0x220 drivers/tty/vt/vt_ioctl.c:995
 process_one_work kernel/workqueue.c:2657 [inline]
 process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2734
 worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2815
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>