syzbot

======================================================
WARNING: possible circular locking dependency detected
6.11.0-rc6-syzkaller-00048-gc7fb1692dc01 #0 Not tainted
------------------------------------------------------
kworker/1:2/1884 is trying to acquire lock:
ffff88801acb10b8 (&buf->lock){+.+.}-{3:3}, at: tty_buffer_flush+0x72/0x310 drivers/tty/tty_buffer.c:229

but task is already holding lock:
ffffffff8dda7160 (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:2735
       con_flush_chars+0x5e/0x80 drivers/tty/vt/vt.c:3503
       n_tty_write+0xe27/0x1150 drivers/tty/n_tty.c:2405
       iterate_tty_write drivers/tty/tty_io.c:1021 [inline]
       file_tty_write.constprop.0+0x518/0x9b0 drivers/tty/tty_io.c:1096
       new_sync_write fs/read_write.c:497 [inline]
       vfs_write+0x6b6/0x1140 fs/read_write.c:590
       ksys_write+0x12f/0x260 fs/read_write.c:643
       do_syscall_32_irqs_on arch/x86/entry/common.c:165 [inline]
       __do_fast_syscall_32+0x73/0x120 arch/x86/entry/common.c:386
       do_fast_syscall_32+0x32/0x80 arch/x86/entry/common.c:411
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

-> #1 (&tty->termios_rwsem){++++}-{3:3}:
       down_write+0x93/0x200 kernel/locking/rwsem.c:1579
       tty_unthrottle+0x1f/0x110 drivers/tty/tty_ioctl.c:103
       hci_uart_tty_receive+0x394/0x780 drivers/bluetooth/hci_ldisc.c:625
       tty_ldisc_receive_buf+0x153/0x190 drivers/tty/tty_buffer.c:391
       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+0x264/0x780 drivers/tty/tty_buffer.c:495
       process_one_work+0x958/0x1ad0 kernel/workqueue.c:3231
       process_scheduled_works kernel/workqueue.c:3312 [inline]
       worker_thread+0x6c8/0xed0 kernel/workqueue.c:3389
       kthread+0x2c1/0x3a0 kernel/kthread.c:389
       ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

-> #0 (&buf->lock){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3133 [inline]
       check_prevs_add kernel/locking/lockdep.c:3252 [inline]
       validate_chain kernel/locking/lockdep.c:3868 [inline]
       __lock_acquire+0x24ed/0x3cb0 kernel/locking/lockdep.c:5142
       lock_acquire kernel/locking/lockdep.c:5759 [inline]
       lock_acquire+0x1b1/0x560 kernel/locking/lockdep.c:5724
       __mutex_lock_common kernel/locking/mutex.c:608 [inline]
       __mutex_lock+0x175/0x9c0 kernel/locking/mutex.c:752
       tty_buffer_flush+0x72/0x310 drivers/tty/tty_buffer.c:229
       tty_ldisc_flush+0x64/0xe0 drivers/tty/tty_ldisc.c:388
       __do_SAK+0x6a1/0x800 drivers/tty/tty_io.c:3038
       vc_SAK+0x7f/0x310 drivers/tty/vt/vt_ioctl.c:993
       process_one_work+0x958/0x1ad0 kernel/workqueue.c:3231
       process_scheduled_works kernel/workqueue.c:3312 [inline]
       worker_thread+0x6c8/0xed0 kernel/workqueue.c:3389
       kthread+0x2c1/0x3a0 kernel/kthread.c:389
       ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

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/1:2/1884:
 #0: ffff88801ac88948 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x11f0/0x1ad0 kernel/workqueue.c:3206
 #1: ffffc9000ca8fd80 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_one_work+0x8bb/0x1ad0 kernel/workqueue.c:3207
 #2: ffffffff8dda7160 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x13/0x310 drivers/tty/vt/vt_ioctl.c:983
 #3: ffff88801281e0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref drivers/tty/tty_ldisc.c:263 [inline]
 #3: ffff88801281e0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_flush+0x1c/0xe0 drivers/tty/tty_ldisc.c:386

stack backtrace:
CPU: 1 UID: 0 PID: 1884 Comm: kworker/1:2 Not tainted 6.11.0-rc6-syzkaller-00048-gc7fb1692dc01 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Workqueue: events vc_SAK
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:93 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:119
 check_noncircular+0x31a/0x400 kernel/locking/lockdep.c:2186
 check_prev_add kernel/locking/lockdep.c:3133 [inline]
 check_prevs_add kernel/locking/lockdep.c:3252 [inline]
 validate_chain kernel/locking/lockdep.c:3868 [inline]
 __lock_acquire+0x24ed/0x3cb0 kernel/locking/lockdep.c:5142
 lock_acquire kernel/locking/lockdep.c:5759 [inline]
 lock_acquire+0x1b1/0x560 kernel/locking/lockdep.c:5724
 __mutex_lock_common kernel/locking/mutex.c:608 [inline]
 __mutex_lock+0x175/0x9c0 kernel/locking/mutex.c:752
 tty_buffer_flush+0x72/0x310 drivers/tty/tty_buffer.c:229
 tty_ldisc_flush+0x64/0xe0 drivers/tty/tty_ldisc.c:388
 __do_SAK+0x6a1/0x800 drivers/tty/tty_io.c:3038
 vc_SAK+0x7f/0x310 drivers/tty/vt/vt_ioctl.c:993
 process_one_work+0x958/0x1ad0 kernel/workqueue.c:3231
 process_scheduled_works kernel/workqueue.c:3312 [inline]
 worker_thread+0x6c8/0xed0 kernel/workqueue.c:3389
 kthread+0x2c1/0x3a0 kernel/kthread.c:389
 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>
tty tty1: SAK: killed process 11375 (syz.3.1667): by fd#10