====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ kworker/0:6/4325 is trying to acquire lock: ffff8880529372e8 (&tty->termios_rwsem){++++}-{3:3}, at: n_tty_flush_buffer+0x2c/0x210 drivers/tty/n_tty.c:370 but task is already holding lock: ffff8880176280b8 (&buf->lock){+.+.}-{3:3}, at: tty_buffer_flush+0x78/0x3e0 drivers/tty/tty_buffer.c:230 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #3 (&buf->lock){+.+.}-{3:3}: __mutex_lock_common kernel/locking/mutex.c:603 [inline] __mutex_lock+0x12d/0xae0 kernel/locking/mutex.c:747 tty_buffer_flush+0x78/0x3e0 drivers/tty/tty_buffer.c:230 tty_ldisc_flush+0x6a/0xc0 drivers/tty/tty_ldisc.c:389 __do_SAK+0x25c/0x630 drivers/tty/tty_io.c:3011 vc_SAK+0x74/0x210 drivers/tty/vt/vt_ioctl.c:995 process_one_work+0x8ab/0x1160 kernel/workqueue.c:2292 worker_thread+0xaf5/0x12a0 kernel/workqueue.c:2439 kthread+0x29d/0x330 kernel/kthread.c:376 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 -> #2 (console_lock){+.+.}-{0:0}: console_lock+0x160/0x1c0 kernel/printk/printk.c:2629 uart_configure_port drivers/tty/serial/serial_core.c:2576 [inline] uart_add_one_port+0x828/0x1e70 drivers/tty/serial/serial_core.c:3135 serial8250_register_8250_port+0x1321/0x1b40 drivers/tty/serial/8250/8250_core.c:1092 serial_pnp_probe+0x56f/0x750 drivers/tty/serial/8250/8250_pnp.c:478 pnp_device_probe+0x301/0x4b0 drivers/pnp/driver.c:111 call_driver_probe drivers/base/dd.c:-1 [inline] really_probe+0x24a/0xb40 drivers/base/dd.c:638 __driver_probe_device+0x1f5/0x390 drivers/base/dd.c:804 driver_probe_device+0x4f/0x420 drivers/base/dd.c:834 __driver_attach+0x43d/0x6c0 drivers/base/dd.c:1220 bus_for_each_dev+0x182/0x1f0 drivers/base/bus.c:303 bus_add_driver+0x324/0x5d0 drivers/base/bus.c:620 driver_register+0x32d/0x430 drivers/base/driver.c:246 serial8250_init+0x96/0x161 drivers/tty/serial/8250/8250_core.c:1191 do_one_initcall+0x257/0x800 init/main.c:1309 do_initcall_level+0x13d/0x1ed init/main.c:1382 do_initcalls+0x4b/0x8a init/main.c:1398 kernel_init_freeable+0x401/0x5ab init/main.c:1637 kernel_init+0x19/0x1b0 init/main.c:1525 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 -> #1 (&port->mutex){+.+.}-{3:3}: __mutex_lock_common kernel/locking/mutex.c:603 [inline] __mutex_lock+0x12d/0xae0 kernel/locking/mutex.c:747 uart_set_termios+0x80/0x900 drivers/tty/serial/serial_core.c:1651 tty_set_termios+0xcad/0x17e0 drivers/tty/tty_ioctl.c:363 set_termios+0x4fe/0x680 drivers/tty/tty_ioctl.c:537 tty_mode_ioctl+0x51e/0x6a0 drivers/tty/tty_ioctl.c:-1 tty_ioctl+0x878/0xba0 drivers/tty/tty_io.c:2785 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:870 [inline] __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:856 do_syscall_x64 arch/x86/entry/common.c:46 [inline] do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76 entry_SYSCALL_64_after_hwframe+0x68/0xd2 -> #0 (&tty->termios_rwsem){++++}-{3:3}: check_prev_add kernel/locking/lockdep.c:3095 [inline] check_prevs_add kernel/locking/lockdep.c:3214 [inline] validate_chain kernel/locking/lockdep.c:3830 [inline] __lock_acquire+0x2d18/0x7c40 kernel/locking/lockdep.c:5063 lock_acquire+0x1bb/0x4a0 kernel/locking/lockdep.c:5676 down_write+0x36/0x60 kernel/locking/rwsem.c:1573 n_tty_flush_buffer+0x2c/0x210 drivers/tty/n_tty.c:370 tty_buffer_flush+0x31d/0x3e0 drivers/tty/tty_buffer.c:242 tty_ldisc_flush+0x6a/0xc0 drivers/tty/tty_ldisc.c:389 __do_SAK+0x25c/0x630 drivers/tty/tty_io.c:3011 vc_SAK+0x74/0x210 drivers/tty/vt/vt_ioctl.c:995 process_one_work+0x8ab/0x1160 kernel/workqueue.c:2292 worker_thread+0xaf5/0x12a0 kernel/workqueue.c:2439 kthread+0x29d/0x330 kernel/kthread.c:376 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 other info that might help us debug this: Chain exists of: &tty->termios_rwsem --> console_lock --> &buf->lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&buf->lock); lock(console_lock); lock(&buf->lock); lock(&tty->termios_rwsem); *** DEADLOCK *** 5 locks held by kworker/0:6/4325: #0: ffff888017470938 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x7b4/0x1160 kernel/workqueue.c:2267 #1: ffffc9000481fd00 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_one_work+0x7b4/0x1160 kernel/workqueue.c:2267 #2: ffffffff8cb21e20 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x24/0x210 drivers/tty/vt/vt_ioctl.c:985 #3: ffff888052937098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref drivers/tty/tty_ldisc.c:264 [inline] #3: ffff888052937098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_flush+0x1c/0xc0 drivers/tty/tty_ldisc.c:387 #4: ffff8880176280b8 (&buf->lock){+.+.}-{3:3}, at: tty_buffer_flush+0x78/0x3e0 drivers/tty/tty_buffer.c:230 stack backtrace: CPU: 0 PID: 4325 Comm: kworker/0:6 Not tainted syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026 Workqueue: events vc_SAK Call Trace: dump_stack_lvl+0x188/0x24e lib/dump_stack.c:106 check_noncircular+0x296/0x330 kernel/locking/lockdep.c:2170 check_prev_add kernel/locking/lockdep.c:3095 [inline] check_prevs_add kernel/locking/lockdep.c:3214 [inline] validate_chain kernel/locking/lockdep.c:3830 [inline] __lock_acquire+0x2d18/0x7c40 kernel/locking/lockdep.c:5063 lock_acquire+0x1bb/0x4a0 kernel/locking/lockdep.c:5676 down_write+0x36/0x60 kernel/locking/rwsem.c:1573 n_tty_flush_buffer+0x2c/0x210 drivers/tty/n_tty.c:370 tty_buffer_flush+0x31d/0x3e0 drivers/tty/tty_buffer.c:242 tty_ldisc_flush+0x6a/0xc0 drivers/tty/tty_ldisc.c:389 __do_SAK+0x25c/0x630 drivers/tty/tty_io.c:3011 vc_SAK+0x74/0x210 drivers/tty/vt/vt_ioctl.c:995 process_one_work+0x8ab/0x1160 kernel/workqueue.c:2292 worker_thread+0xaf5/0x12a0 kernel/workqueue.c:2439 kthread+0x29d/0x330 kernel/kthread.c:376 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 tty tty1: SAK: killed process 4427 (syz.0.20): by fd#3 tty tty1: SAK: killed process 4429 (syz.0.20): by fd#3