======================================================
WARNING: possible circular locking dependency detected
6.16.0-rc4-syzkaller-00308-ga79a588fc176 #0 Not tainted
------------------------------------------------------
kworker/1:4/5919 is trying to acquire lock:
ffff88801a4a10b8 (&buf->lock){+.+.}-{4:4}, at: tty_buffer_flush+0x74/0x2b0 drivers/tty/tty_buffer.c:229

but task is already holding lock:
ffffffff8e1330a0 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x28/0x220 drivers/tty/vt/vt_ioctl.c:999

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (console_lock){+.+.}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       console_lock+0x164/0x1b0 kernel/printk/printk.c:2849
       con_flush_chars+0x70/0x280 drivers/tty/vt/vt.c:3585
       n_tty_write+0xede/0x11d0 drivers/tty/n_tty.c:2393
       iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
       file_tty_write+0x500/0x990 drivers/tty/tty_io.c:1081
       do_iter_readv_writev+0x56e/0x7f0 fs/read_write.c:-1
       vfs_writev+0x31a/0x960 fs/read_write.c:1057
       do_writev+0x14d/0x2d0 fs/read_write.c:1103
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&tty->termios_rwsem){++++}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       down_read+0x46/0x2e0 kernel/locking/rwsem.c:1524
       n_tty_receive_buf_common+0x84/0x12f0 drivers/tty/n_tty.c:1686
       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+0x24a/0x720 drivers/tty/tty_buffer.c:495
       process_one_work kernel/workqueue.c:3238 [inline]
       process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3321
       worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402
       kthread+0x711/0x8a0 kernel/kthread.c:464
       ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #0 (&buf->lock){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3168 [inline]
       check_prevs_add kernel/locking/lockdep.c:3287 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
       tty_buffer_flush+0x74/0x2b0 drivers/tty/tty_buffer.c:229
       tty_ldisc_flush+0x6b/0xc0 drivers/tty/tty_ldisc.c:388
       __do_SAK+0x138/0x6d0 drivers/tty/tty_io.c:3025
       vc_SAK+0x78/0x220 drivers/tty/vt/vt_ioctl.c:1009
       process_one_work kernel/workqueue.c:3238 [inline]
       process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3321
       worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402
       kthread+0x711/0x8a0 kernel/kthread.c:464
       ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

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/1:4/5919:
 #0: ffff88801a480d48 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3213 [inline]
 #0: ffff88801a480d48 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x17b0 kernel/workqueue.c:3321
 #1: ffffc9000442fbc0 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3214 [inline]
 #1: ffffc9000442fbc0 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x17b0 kernel/workqueue.c:3321
 #2: ffffffff8e1330a0 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x28/0x220 drivers/tty/vt/vt_ioctl.c:999
 #3: ffff88807edf30a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref drivers/tty/tty_ldisc.c:263 [inline]
 #3: ffff88807edf30a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_flush+0x20/0xc0 drivers/tty/tty_ldisc.c:386

stack backtrace:
CPU: 1 UID: 0 PID: 5919 Comm: kworker/1:4 Not tainted 6.16.0-rc4-syzkaller-00308-ga79a588fc176 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Workqueue: events vc_SAK
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2046
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3168 [inline]
 check_prevs_add kernel/locking/lockdep.c:3287 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
 __mutex_lock_common kernel/locking/mutex.c:602 [inline]
 __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
 tty_buffer_flush+0x74/0x2b0 drivers/tty/tty_buffer.c:229
 tty_ldisc_flush+0x6b/0xc0 drivers/tty/tty_ldisc.c:388
 __do_SAK+0x138/0x6d0 drivers/tty/tty_io.c:3025
 vc_SAK+0x78/0x220 drivers/tty/vt/vt_ioctl.c:1009
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3321
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402
 kthread+0x711/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>