Kernel bug: possible deadlock in tty_buffer_flush (3)
Subsystem: serial
Status: open

Crash report:
======================================================
WARNING: possible circular locking dependency detected
6.13.0-rc7-syzkaller-00189-g595523945be0 #0 Not tainted
------------------------------------------------------
kworker/1:4/5864 is trying to acquire lock:
ffff88801b0990b8 (&buf->lock){+.+.}-{4:4}, at: tty_buffer_flush+0x72/0x310 drivers/tty/tty_buffer.c:229

but task is already holding lock:
ffffffff8e1a9040 (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:2833
       con_flush_chars+0x5e/0x80 drivers/tty/vt/vt.c:3503
       __receive_buf drivers/tty/n_tty.c:1644 [inline]
       n_tty_receive_buf_common+0xa99/0x1980 drivers/tty/n_tty.c:1739
       tty_ldisc_receive_buf+0xa2/0x190 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+0x264/0x780 drivers/tty/tty_buffer.c:495
       process_one_work+0x9c5/0x1ba0 kernel/workqueue.c:3236
       process_scheduled_works kernel/workqueue.c:3317 [inline]
       worker_thread+0x6c8/0xf00 kernel/workqueue.c:3398
       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

-> #1 (&tty->termios_rwsem){++++}-{4:4}:
       down_read+0x9a/0x330 kernel/locking/rwsem.c:1524
       n_tty_receive_buf_common+0x85/0x1980 drivers/tty/n_tty.c:1702
       tty_ldisc_receive_buf+0xa2/0x190 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+0x264/0x780 drivers/tty/tty_buffer.c:495
       process_one_work+0x9c5/0x1ba0 kernel/workqueue.c:3236
       process_scheduled_works kernel/workqueue.c:3317 [inline]
       worker_thread+0x6c8/0xf00 kernel/workqueue.c:3398
       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){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3161 [inline]
       check_prevs_add kernel/locking/lockdep.c:3280 [inline]
       validate_chain kernel/locking/lockdep.c:3904 [inline]
       __lock_acquire+0x249e/0x3c40 kernel/locking/lockdep.c:5226
       lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5849
       __mutex_lock_common kernel/locking/mutex.c:585 [inline]
       __mutex_lock+0x19b/0xa60 kernel/locking/mutex.c:735
       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+0x9c5/0x1ba0 kernel/workqueue.c:3236
       process_scheduled_works kernel/workqueue.c:3317 [inline]
       worker_thread+0x6c8/0xf00 kernel/workqueue.c:3398
       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/1:4/5864:
 #0: ffff88801b078948 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x1293/0x1ba0 kernel/workqueue.c:3211
 #1: ffffc90004a9fd80 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_one_work+0x921/0x1ba0 kernel/workqueue.c:3212
 #2: ffffffff8e1a9040 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x13/0x310 drivers/tty/vt/vt_ioctl.c:983
 #3: ffff8880698950a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref drivers/tty/tty_ldisc.c:263 [inline]
 #3: ffff8880698950a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_flush+0x1c/0xe0 drivers/tty/tty_ldisc.c:386

stack backtrace:
CPU: 1 UID: 0 PID: 5864 Comm: kworker/1:4 Not tainted 6.13.0-rc7-syzkaller-00189-g595523945be0 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
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+0x419/0x5d0 kernel/locking/lockdep.c:2074
 check_noncircular+0x31a/0x400 kernel/locking/lockdep.c:2206
 check_prev_add kernel/locking/lockdep.c:3161 [inline]
 check_prevs_add kernel/locking/lockdep.c:3280 [inline]
 validate_chain kernel/locking/lockdep.c:3904 [inline]
 __lock_acquire+0x249e/0x3c40 kernel/locking/lockdep.c:5226
 lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5849
 __mutex_lock_common kernel/locking/mutex.c:585 [inline]
 __mutex_lock+0x19b/0xa60 kernel/locking/mutex.c:735
 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+0x9c5/0x1ba0 kernel/workqueue.c:3236
 process_scheduled_works kernel/workqueue.c:3317 [inline]
 worker_thread+0x6c8/0xf00 kernel/workqueue.c:3398
 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 5889 (syz-executor496): by fd#4
usb 2-1: USB disconnect, device number 3
usb 2-1: new high-speed USB device number 4 using dummy_hcd
usb 2-1: config 0 interface 0 altsetting 0 endpoint 0x81 has an invalid bInterval 0, changing to 7
usb 2-1: New USB device found, idVendor=0926, idProduct=3333, bcdDevice= 0.40
usb 2-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
usb 2-1: config 0 descriptor??
keytouch 0003:0926:3333.000F: fixing up Keytouch IEC report descriptor
input: HID 0926:3333 as /devices/platform/dummy_hcd.1/usb2/2-1/2-1:0.0/0003:0926:3333.000F/input/input19
keytouch 0003:0926:3333.000F: input,hidraw2: USB HID v0.00 Keyboard [HID 0926:3333] on usb-dummy_hcd.1-1/input0