====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ kworker/0:1/11 is trying to acquire lock: ffff0000d47b12c8 (&tty->termios_rwsem){++++}-{4:4}, at: class_rwsem_write_constructor include/linux/rwsem.h:270 [inline] ffff0000d47b12c8 (&tty->termios_rwsem){++++}-{4:4}, at: n_tty_flush_buffer+0x2c/0xa4 drivers/tty/n_tty.c:349 but task is already holding lock: ffff0000c006a0b8 (&buf->lock){+.+.}-{4:4}, at: tty_buffer_flush+0x78/0x2b4 drivers/tty/tty_buffer.c:236 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #4 (&buf->lock){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x164/0xf14 kernel/locking/mutex.c:821 mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874 tty_buffer_flush+0x78/0x2b4 drivers/tty/tty_buffer.c:236 tty_ldisc_flush+0x30/0x7c drivers/tty/tty_ldisc.c:388 __do_SAK+0x21c/0x604 drivers/tty/tty_io.c:3025 vc_SAK+0x74/0xa4 drivers/tty/vt/vt_ioctl.c:994 process_one_work kernel/workqueue.c:3322 [inline] process_scheduled_works+0x788/0x10b8 kernel/workqueue.c:3405 worker_thread+0x798/0xbd0 kernel/workqueue.c:3486 kthread+0x304/0x3d4 kernel/kthread.c:436 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:842 -> #3 (console_lock){+.+.}-{0:0}: console_lock+0x8c/0xac kernel/printk/printk.c:2896 console_call_setup+0x54/0xa4 kernel/printk/printk.c:3881 try_enable_preferred_console+0x444/0x5a4 kernel/printk/printk.c:3926 register_console+0x3a0/0xb98 kernel/printk/printk.c:4120 univ8250_console_init+0x5c/0x84 drivers/tty/serial/8250/8250_core.c:515 console_init+0x14c/0x89c kernel/printk/printk.c:4407 start_kernel+0x25c/0x3c0 init/main.c:1112 __primary_switched+0x8c/0x94 arch/arm64/kernel/head.S:246 -> #2 (console_mutex){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x164/0xf14 kernel/locking/mutex.c:821 mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874 console_list_lock+0x90/0xa8 kernel/printk/printk.c:263 console_is_registered include/linux/console.h:573 [inline] uart_configure_port drivers/tty/serial/serial_core.c:2574 [inline] serial_core_add_one_port drivers/tty/serial/serial_core.c:3101 [inline] serial_core_register_port+0x1284/0x1b0c drivers/tty/serial/serial_core.c:3322 serial_ctrl_register_port+0x28/0x38 drivers/tty/serial/serial_ctrl.c:41 uart_add_one_port+0x28/0x38 drivers/tty/serial/serial_port.c:143 pl011_register_port+0x194/0x2ec drivers/tty/serial/amba-pl011.c:2989 sbsa_uart_probe+0x334/0x46c drivers/tty/serial/amba-pl011.c:3163 platform_probe+0x100/0x1a4 drivers/base/platform.c:1439 call_driver_probe drivers/base/dd.c:-1 [inline] really_probe+0x29c/0x800 drivers/base/dd.c:706 __driver_probe_device+0x1e0/0x350 drivers/base/dd.c:868 driver_probe_device+0x6c/0x19c drivers/base/dd.c:898 __device_attach_driver+0x198/0x2f8 drivers/base/dd.c:1026 bus_for_each_drv+0x144/0x1dc drivers/base/bus.c:500 __device_attach+0x248/0x390 drivers/base/dd.c:1098 device_initial_probe+0x90/0xc8 drivers/base/dd.c:1153 bus_probe_device+0x58/0x120 drivers/base/bus.c:620 device_add+0x6cc/0x9e0 drivers/base/core.c:3772 platform_device_add+0x3dc/0x6f0 drivers/base/platform.c:762 platform_device_register_full+0x4fc/0x5ac drivers/base/platform.c:902 acpi_create_platform_device+0x50c/0x6e4 drivers/acpi/acpi_platform.c:181 acpi_default_enumeration+0x200/0x438 drivers/acpi/scan.c:2281 acpi_bus_attach+0x64c/0x7e0 drivers/acpi/scan.c:2390 acpi_dev_for_one_check+0xa0/0xb4 drivers/acpi/bus.c:1278 device_for_each_child+0xf4/0x184 drivers/base/core.c:4101 acpi_dev_for_each_child+0x98/0xe4 drivers/acpi/bus.c:1290 acpi_bus_attach+0x20c/0x7e0 drivers/acpi/scan.c:2395 acpi_dev_for_one_check+0xa0/0xb4 drivers/acpi/bus.c:1278 device_for_each_child+0xf4/0x184 drivers/base/core.c:4101 acpi_dev_for_each_child+0x98/0xe4 drivers/acpi/bus.c:1290 acpi_bus_attach+0x20c/0x7e0 drivers/acpi/scan.c:2395 acpi_bus_scan+0x104/0x310 drivers/acpi/scan.c:2745 acpi_scan_init+0x168/0x3cc drivers/acpi/scan.c:2871 acpi_init+0x15c/0x1f4 drivers/acpi/bus.c:1605 do_one_initcall+0x274/0xc38 init/main.c:1347 do_initcall_level+0x12c/0x1c4 init/main.c:1409 do_initcalls+0x70/0xd0 init/main.c:1425 do_basic_setup+0x7c/0x90 init/main.c:1445 kernel_init_freeable+0x268/0x3a8 init/main.c:1658 kernel_init+0x24/0x1dc init/main.c:1548 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:842 -> #1 (&port->mutex){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x164/0xf14 kernel/locking/mutex.c:821 mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874 class_mutex_constructor include/linux/mutex.h:253 [inline] uart_set_termios+0x74/0x58c drivers/tty/serial/serial_core.c:1645 tty_set_termios+0x3b0/0x6d0 drivers/tty/tty_ioctl.c:341 set_termios+0x428/0x618 drivers/tty/tty_ioctl.c:516 tty_mode_ioctl+0x45c/0x7f4 drivers/tty/tty_ioctl.c:-1 n_tty_ioctl_helper+0xa8/0x2d8 drivers/tty/tty_ioctl.c:982 n_tty_ioctl+0x190/0x434 drivers/tty/n_tty.c:2496 tty_ioctl+0x900/0xd50 drivers/tty/tty_io.c:2801 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl fs/ioctl.c:583 [inline] __arm64_sys_ioctl+0x154/0x1cc fs/ioctl.c:583 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline] invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140 el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736 el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594 -> #0 (&tty->termios_rwsem){++++}-{4:4}: check_prev_add kernel/locking/lockdep.c:3165 [inline] check_prevs_add kernel/locking/lockdep.c:3284 [inline] validate_chain kernel/locking/lockdep.c:3908 [inline] __lock_acquire+0x17c0/0x2ebc kernel/locking/lockdep.c:5237 lock_acquire+0x140/0x364 kernel/locking/lockdep.c:5868 down_write+0x50/0xc0 kernel/locking/rwsem.c:1631 class_rwsem_write_constructor include/linux/rwsem.h:270 [inline] n_tty_flush_buffer+0x2c/0xa4 drivers/tty/n_tty.c:349 tty_buffer_flush+0x1b8/0x2b4 drivers/tty/tty_buffer.c:248 tty_ldisc_flush+0x30/0x7c drivers/tty/tty_ldisc.c:388 __do_SAK+0x21c/0x604 drivers/tty/tty_io.c:3025 vc_SAK+0x74/0xa4 drivers/tty/vt/vt_ioctl.c:994 process_one_work kernel/workqueue.c:3322 [inline] process_scheduled_works+0x788/0x10b8 kernel/workqueue.c:3405 worker_thread+0x798/0xbd0 kernel/workqueue.c:3486 kthread+0x304/0x3d4 kernel/kthread.c:436 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:842 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/0:1/11: #0: ffff0000c002b540 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3297 [inline] #0: ffff0000c002b540 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x734/0x10b8 kernel/workqueue.c:3405 #1: ffff80008ec47c40 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3297 [inline] #1: ffff80008ec47c40 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_scheduled_works+0x73c/0x10b8 kernel/workqueue.c:3405 #2: ffff800088cec860 (console_lock){+.+.}-{0:0}, at: class_console_lock_constructor include/linux/console.h:734 [inline] #2: ffff800088cec860 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x2c/0xa4 drivers/tty/vt/vt_ioctl.c:985 #3: ffff0000d47b10a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref+0x20/0x90 drivers/tty/tty_ldisc.c:263 #4: ffff0000c006a0b8 (&buf->lock){+.+.}-{4:4}, at: tty_buffer_flush+0x78/0x2b4 drivers/tty/tty_buffer.c:236 stack backtrace: CPU: 0 UID: 0 PID: 11 Comm: kworker/0:1 Not tainted syzkaller #0 PREEMPT Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/02/2026 Workqueue: events vc_SAK Call trace: show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C) __dump_stack+0x30/0x40 lib/dump_stack.c:94 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120 dump_stack+0x1c/0x28 lib/dump_stack.c:129 print_circular_bug+0x328/0x330 kernel/locking/lockdep.c:2043 check_noncircular+0x158/0x174 kernel/locking/lockdep.c:2175 check_prev_add kernel/locking/lockdep.c:3165 [inline] check_prevs_add kernel/locking/lockdep.c:3284 [inline] validate_chain kernel/locking/lockdep.c:3908 [inline] __lock_acquire+0x17c0/0x2ebc kernel/locking/lockdep.c:5237 lock_acquire+0x140/0x364 kernel/locking/lockdep.c:5868 down_write+0x50/0xc0 kernel/locking/rwsem.c:1631 class_rwsem_write_constructor include/linux/rwsem.h:270 [inline] n_tty_flush_buffer+0x2c/0xa4 drivers/tty/n_tty.c:349 tty_buffer_flush+0x1b8/0x2b4 drivers/tty/tty_buffer.c:248 tty_ldisc_flush+0x30/0x7c drivers/tty/tty_ldisc.c:388 __do_SAK+0x21c/0x604 drivers/tty/tty_io.c:3025 vc_SAK+0x74/0xa4 drivers/tty/vt/vt_ioctl.c:994 process_one_work kernel/workqueue.c:3322 [inline] process_scheduled_works+0x788/0x10b8 kernel/workqueue.c:3405 worker_thread+0x798/0xbd0 kernel/workqueue.c:3486 kthread+0x304/0x3d4 kernel/kthread.c:436 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:842