====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ kworker/0:1/9 is trying to acquire lock: ffff8880790722e8 (&tty->termios_rwsem){++++}-{3:3}, at: n_tty_flush_buffer+0x30/0x230 drivers/tty/n_tty.c:363 but task is already holding lock: ffff8880186510b8 (&buf->lock){+.+.}-{3:3}, at: tty_buffer_flush+0x79/0x3e0 drivers/tty/tty_buffer.c:229 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+0x135/0xc80 kernel/locking/mutex.c:747 tty_buffer_flush+0x79/0x3e0 drivers/tty/tty_buffer.c:229 tty_ldisc_flush+0x6b/0xc0 drivers/tty/tty_ldisc.c:388 __do_SAK+0x25b/0x680 drivers/tty/tty_io.c:3014 vc_SAK+0x78/0x220 drivers/tty/vt/vt_ioctl.c:995 process_one_work kernel/workqueue.c:2657 [inline] process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2734 worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2815 kthread+0x2fa/0x390 kernel/kthread.c:388 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293 -> #2 (console_lock){+.+.}-{0:0}: console_lock+0x164/0x1b0 kernel/printk/printk.c:2686 uart_configure_port drivers/tty/serial/serial_core.c:2632 [inline] serial_core_add_one_port drivers/tty/serial/serial_core.c:3199 [inline] serial_core_register_port+0xbee/0x20b0 drivers/tty/serial/serial_core.c:3422 serial8250_register_8250_port+0x15fd/0x1f40 drivers/tty/serial/8250/8250_core.c:1142 serial_pnp_probe+0x577/0x750 drivers/tty/serial/8250/8250_pnp.c:478 pnp_device_probe+0x305/0x4b0 drivers/pnp/driver.c:111 call_driver_probe drivers/base/dd.c:-1 [inline] really_probe+0x247/0xae0 drivers/base/dd.c:717 __driver_probe_device+0x1f5/0x390 drivers/base/dd.c:879 driver_probe_device+0x4f/0x420 drivers/base/dd.c:909 __driver_attach+0x444/0x6d0 drivers/base/dd.c:1295 bus_for_each_dev+0x235/0x2b0 drivers/base/bus.c:370 bus_add_driver+0x340/0x630 drivers/base/bus.c:723 driver_register+0x23a/0x310 drivers/base/driver.c:246 serial8250_init+0x9a/0x170 drivers/tty/serial/8250/8250_core.c:1243 do_one_initcall+0x242/0x790 init/main.c:1210 do_initcall_level+0x13d/0x1f0 init/main.c:1272 do_initcalls+0x69/0xd0 init/main.c:1288 kernel_init_freeable+0x3d9/0x560 init/main.c:1525 kernel_init+0x1d/0x1c0 init/main.c:1415 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293 -> #1 (&port->mutex){+.+.}-{3:3}: __mutex_lock_common kernel/locking/mutex.c:603 [inline] __mutex_lock+0x135/0xc80 kernel/locking/mutex.c:747 uart_set_termios+0x84/0x900 drivers/tty/serial/serial_core.c:1703 tty_set_termios+0xcb1/0x17e0 drivers/tty/tty_ioctl.c:354 set_termios+0x52b/0x6c0 drivers/tty/tty_ioctl.c:528 tty_mode_ioctl+0x49f/0x7b0 drivers/tty/tty_ioctl.c:-1 tty_ioctl+0x9b5/0xdc0 drivers/tty/tty_io.c:2788 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:871 [inline] __se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857 do_syscall_x64 arch/x86/entry/common.c:46 [inline] do_syscall_64+0x55/0xb0 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:3134 [inline] check_prevs_add kernel/locking/lockdep.c:3253 [inline] validate_chain kernel/locking/lockdep.c:3869 [inline] __lock_acquire+0x37ef/0x7d80 kernel/locking/lockdep.c:5137 lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5754 down_write+0x97/0x200 kernel/locking/rwsem.c:1573 n_tty_flush_buffer+0x30/0x230 drivers/tty/n_tty.c:363 tty_buffer_flush+0x31e/0x3e0 drivers/tty/tty_buffer.c:241 tty_ldisc_flush+0x6b/0xc0 drivers/tty/tty_ldisc.c:388 __do_SAK+0x25b/0x680 drivers/tty/tty_io.c:3014 vc_SAK+0x78/0x220 drivers/tty/vt/vt_ioctl.c:995 process_one_work kernel/workqueue.c:2657 [inline] process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2734 worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2815 kthread+0x2fa/0x390 kernel/kthread.c:388 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293 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/0:1/9: #0: ffff888017c70938 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2632 [inline] #0: ffff888017c70938 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2734 #1: ffffc900000e7d00 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2632 [inline] #1: ffffc900000e7d00 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2734 #2: ffffffff8d126180 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x28/0x220 drivers/tty/vt/vt_ioctl.c:985 #3: ffff8880790720a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref drivers/tty/tty_ldisc.c:263 [inline] #3: ffff8880790720a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_flush+0x20/0xc0 drivers/tty/tty_ldisc.c:386 #4: ffff8880186510b8 (&buf->lock){+.+.}-{3:3}, at: tty_buffer_flush+0x79/0x3e0 drivers/tty/tty_buffer.c:229 stack backtrace: CPU: 0 PID: 9 Comm: kworker/0:1 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+0x18c/0x250 lib/dump_stack.c:106 check_noncircular+0x2fc/0x400 kernel/locking/lockdep.c:2187 check_prev_add kernel/locking/lockdep.c:3134 [inline] check_prevs_add kernel/locking/lockdep.c:3253 [inline] validate_chain kernel/locking/lockdep.c:3869 [inline] __lock_acquire+0x37ef/0x7d80 kernel/locking/lockdep.c:5137 lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5754 down_write+0x97/0x200 kernel/locking/rwsem.c:1573 n_tty_flush_buffer+0x30/0x230 drivers/tty/n_tty.c:363 tty_buffer_flush+0x31e/0x3e0 drivers/tty/tty_buffer.c:241 tty_ldisc_flush+0x6b/0xc0 drivers/tty/tty_ldisc.c:388 __do_SAK+0x25b/0x680 drivers/tty/tty_io.c:3014 vc_SAK+0x78/0x220 drivers/tty/vt/vt_ioctl.c:995 process_one_work kernel/workqueue.c:2657 [inline] process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2734 worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2815 kthread+0x2fa/0x390 kernel/kthread.c:388 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293 tty tty1: SAK: killed process 6964 (syz.5.111): by fd#3 tty tty1: SAK: killed process 6965 (syz.5.111): by fd#3 tty tty1: SAK: killed process 6967 (syz.5.111): by fd#3