======================================================
WARNING: possible circular locking dependency detected
6.15.0-rc2-syzkaller-00087-gcfb2e2c57aef #0 Not tainted
------------------------------------------------------
kworker/0:4/5877 is trying to acquire lock:
ffff88801b4990b8 (&buf->lock){+.+.}-{4:4}, at: tty_buffer_flush+0x72/0x310 drivers/tty/tty_buffer.c:229

but task is already holding lock:
ffffffff8e3aee40 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x13/0x310 drivers/tty/vt/vt_ioctl.c:983

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (console_lock){+.+.}-{0:0}:
       console_lock+0x7a/0xa0 kernel/printk/printk.c:2849
       con_flush_chars+0x5e/0x80 drivers/tty/vt/vt.c:3501
       __receive_buf drivers/tty/n_tty.c:1628 [inline]
       n_tty_receive_buf_common+0xa97/0x1980 drivers/tty/n_tty.c:1723
       tty_ldisc_receive_buf+0xa7/0x1a0 drivers/tty/tty_buffer.c:387
       tty_port_default_receive_buf+0x70/0xb0 drivers/tty/tty_port.c:37
       receive_buf drivers/tty/tty_buffer.c:445 [inline]
       flush_to_ldisc+0x268/0x780 drivers/tty/tty_buffer.c:495
       process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3238
       process_scheduled_works kernel/workqueue.c:3319 [inline]
       worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
       kthread+0x3c2/0x780 kernel/kthread.c:464
       ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:153
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #1 (&tty->termios_rwsem){++++}-{4:4}:
       down_read+0x9b/0x480 kernel/locking/rwsem.c:1524
       n_tty_receive_buf_common+0x85/0x1980 drivers/tty/n_tty.c:1686
       tty_ldisc_receive_buf+0xa7/0x1a0 drivers/tty/tty_buffer.c:387
       tty_port_default_receive_buf+0x70/0xb0 drivers/tty/tty_port.c:37
       receive_buf drivers/tty/tty_buffer.c:445 [inline]
       flush_to_ldisc+0x268/0x780 drivers/tty/tty_buffer.c:495
       process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3238
       process_scheduled_works kernel/workqueue.c:3319 [inline]
       worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
       kthread+0x3c2/0x780 kernel/kthread.c:464
       ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:153
       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:3166 [inline]
       check_prevs_add kernel/locking/lockdep.c:3285 [inline]
       validate_chain kernel/locking/lockdep.c:3909 [inline]
       __lock_acquire+0x1173/0x1ba0 kernel/locking/lockdep.c:5235
       lock_acquire kernel/locking/lockdep.c:5866 [inline]
       lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5823
       __mutex_lock_common kernel/locking/mutex.c:601 [inline]
       __mutex_lock+0x199/0xb90 kernel/locking/mutex.c:746
       tty_buffer_flush+0x72/0x310 drivers/tty/tty_buffer.c:229
       tty_ldisc_flush+0x64/0xe0 drivers/tty/tty_ldisc.c:388
       __do_SAK+0x6ab/0x810 drivers/tty/tty_io.c:3037
       vc_SAK+0x7f/0x310 drivers/tty/vt/vt_ioctl.c:993
       process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3238
       process_scheduled_works kernel/workqueue.c:3319 [inline]
       worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
       kthread+0x3c2/0x780 kernel/kthread.c:464
       ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:153
       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/0:4/5877:
 #0: ffff88801b478d48 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x12a2/0x1b70 kernel/workqueue.c:3213
 #1: ffffc9000403fd18 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_one_work+0x929/0x1b70 kernel/workqueue.c:3214
 #2: ffffffff8e3aee40 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x13/0x310 drivers/tty/vt/vt_ioctl.c:983
 #3: ffff8880755990a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref drivers/tty/tty_ldisc.c:263 [inline]
 #3: ffff8880755990a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_flush+0x1c/0xe0 drivers/tty/tty_ldisc.c:386

stack backtrace:
CPU: 0 UID: 0 PID: 5877 Comm: kworker/0:4 Not tainted 6.15.0-rc2-syzkaller-00087-gcfb2e2c57aef #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Workqueue: events vc_SAK
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x275/0x350 kernel/locking/lockdep.c:2079
 check_noncircular+0x14c/0x170 kernel/locking/lockdep.c:2211
 check_prev_add kernel/locking/lockdep.c:3166 [inline]
 check_prevs_add kernel/locking/lockdep.c:3285 [inline]
 validate_chain kernel/locking/lockdep.c:3909 [inline]
 __lock_acquire+0x1173/0x1ba0 kernel/locking/lockdep.c:5235
 lock_acquire kernel/locking/lockdep.c:5866 [inline]
 lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5823
 __mutex_lock_common kernel/locking/mutex.c:601 [inline]
 __mutex_lock+0x199/0xb90 kernel/locking/mutex.c:746
 tty_buffer_flush+0x72/0x310 drivers/tty/tty_buffer.c:229
 tty_ldisc_flush+0x64/0xe0 drivers/tty/tty_ldisc.c:388
 __do_SAK+0x6ab/0x810 drivers/tty/tty_io.c:3037
 vc_SAK+0x7f/0x310 drivers/tty/vt/vt_ioctl.c:993
 process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3238
 process_scheduled_works kernel/workqueue.c:3319 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
 kthread+0x3c2/0x780 kernel/kthread.c:464
 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
tty tty1: SAK: killed process 6161 (syz.0.16): by fd#3
tty tty1: SAK: killed process 6162 (syz.0.16): by fd#3