ttyS ttyS3: tty_port_close_start: tty->count = 1 port count = 2 ====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Tainted: G L ------------------------------------------------------ syz.0.1522/11361 is trying to acquire lock: ffffffff8df35920 (console_owner){-.-.}-{0:0}, at: rcu_try_lock_acquire include/linux/rcupdate.h:336 [inline] ffffffff8df35920 (console_owner){-.-.}-{0:0}, at: srcu_read_lock_nmisafe include/linux/srcu.h:409 [inline] ffffffff8df35920 (console_owner){-.-.}-{0:0}, at: console_srcu_read_lock kernel/printk/printk.c:289 [inline] ffffffff8df35920 (console_owner){-.-.}-{0:0}, at: console_flush_one_record kernel/printk/printk.c:3192 [inline] ffffffff8df35920 (console_owner){-.-.}-{0:0}, at: console_flush_all+0x11a/0xb00 kernel/printk/printk.c:3289 but task is already holding lock: ffff888021f40d40 (&port->lock#2){-.-.}-{3:3}, at: class_spinlock_irqsave_constructor include/linux/spinlock.h:585 [inline] ffff888021f40d40 (&port->lock#2){-.-.}-{3:3}, at: tty_port_close_start+0x5e/0x580 drivers/tty/tty_port.c:599 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&port->lock#2){-.-.}-{3:3}: __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] _raw_spin_lock_irqsave+0x40/0x60 kernel/locking/spinlock.c:162 class_spinlock_irqsave_constructor include/linux/spinlock.h:585 [inline] tty_port_tty_get drivers/tty/tty_port.c:301 [inline] class_tty_port_tty_constructor include/linux/tty_port.h:280 [inline] tty_port_default_wakeup+0x23/0x170 drivers/tty/tty_port.c:66 serial8250_tx_chars+0x72e/0x970 drivers/tty/serial/8250/8250_port.c:1719 serial8250_handle_irq+0x633/0xbb0 drivers/tty/serial/8250/8250_port.c:1827 serial8250_default_handle_irq+0xbf/0x200 drivers/tty/serial/8250/8250_port.c:1846 serial8250_interrupt+0x8d/0x180 drivers/tty/serial/8250/8250_core.c:86 __handle_irq_event_percpu+0x217/0x970 kernel/irq/handle.c:211 handle_irq_event_percpu kernel/irq/handle.c:248 [inline] handle_irq_event+0x8b/0x1e0 kernel/irq/handle.c:265 handle_edge_irq+0x23b/0xa10 kernel/irq/chip.c:855 generic_handle_irq_desc include/linux/irqdesc.h:172 [inline] handle_irq arch/x86/kernel/irq.c:255 [inline] call_irq_handler arch/x86/kernel/irq.c:-1 [inline] __common_interrupt+0x141/0x1f0 arch/x86/kernel/irq.c:326 common_interrupt+0xb6/0xe0 arch/x86/kernel/irq.c:319 asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:688 default_idle_call+0x9e/0xb0 kernel/sched/idle.c:130 cpuidle_idle_call kernel/sched/idle.c:191 [inline] do_idle+0x1be/0x4d0 kernel/sched/idle.c:332 cpu_startup_entry+0x44/0x60 kernel/sched/idle.c:430 rest_init+0x2de/0x300 init/main.c:757 start_kernel+0x381/0x3d0 init/main.c:1206 x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310 x86_64_start_kernel+0x143/0x1c0 arch/x86/kernel/head64.c:291 common_startup_64+0x13e/0x147 -> #1 (&port_lock_key){-.-.}-{3:3}: __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] _raw_spin_lock_irqsave+0x40/0x60 kernel/locking/spinlock.c:162 uart_port_lock_irqsave include/linux/serial_core.h:717 [inline] serial8250_console_write+0x155/0x1b60 drivers/tty/serial/8250/8250_port.c:3301 console_emit_next_record kernel/printk/printk.c:3129 [inline] console_flush_one_record kernel/printk/printk.c:3215 [inline] console_flush_all+0x713/0xb00 kernel/printk/printk.c:3289 __console_flush_and_unlock kernel/printk/printk.c:3319 [inline] console_unlock+0xbb/0x190 kernel/printk/printk.c:3359 vprintk_emit+0x47b/0x550 kernel/printk/printk.c:2426 _printk+0xcf/0x120 kernel/printk/printk.c:2451 register_console+0xa8b/0xf90 kernel/printk/printk.c:4170 univ8250_console_init+0x3a/0x70 drivers/tty/serial/8250/8250_core.c:515 console_init+0xfc/0x3f0 kernel/printk/printk.c:4369 start_kernel+0x227/0x3d0 init/main.c:1143 x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310 x86_64_start_kernel+0x143/0x1c0 arch/x86/kernel/head64.c:291 common_startup_64+0x13e/0x147 -> #0 (console_owner){-.-.}-{0:0}: 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+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237 lock_acquire+0x107/0x340 kernel/locking/lockdep.c:5868 console_lock_spinning_enable kernel/printk/printk.c:1900 [inline] console_emit_next_record kernel/printk/printk.c:3123 [inline] console_flush_one_record kernel/printk/printk.c:3215 [inline] console_flush_all+0x6bc/0xb00 kernel/printk/printk.c:3289 __console_flush_and_unlock kernel/printk/printk.c:3319 [inline] console_unlock+0xbb/0x190 kernel/printk/printk.c:3359 vprintk_emit+0x47b/0x550 kernel/printk/printk.c:2426 _printk+0xcf/0x120 kernel/printk/printk.c:2451 tty_port_close_start+0x3f4/0x580 drivers/tty/tty_port.c:601 tty_port_close+0x2a/0x170 drivers/tty/tty_port.c:682 tty_release+0x389/0x1720 drivers/tty/tty_io.c:1745 __fput+0x44c/0xa70 fs/file_table.c:468 task_work_run+0x1d4/0x260 kernel/task_work.c:233 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline] __exit_to_user_mode_loop kernel/entry/common.c:44 [inline] exit_to_user_mode_loop+0xef/0x4e0 kernel/entry/common.c:75 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline] syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline] syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline] syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline] do_syscall_64+0x2c1/0xf80 arch/x86/entry/syscall_64.c:100 entry_SYSCALL_64_after_hwframe+0x77/0x7f other info that might help us debug this: Chain exists of: console_owner --> &port_lock_key --> &port->lock#2 Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&port->lock#2); lock(&port_lock_key); lock(&port->lock#2); lock(console_owner); *** DEADLOCK *** 4 locks held by syz.0.1522/11361: #0: ffff888031b871c0 (&tty->legacy_mutex){+.+.}-{4:4}, at: tty_release+0x72/0x1720 drivers/tty/tty_io.c:1727 #1: ffff888021f40d40 (&port->lock#2){-.-.}-{3:3}, at: class_spinlock_irqsave_constructor include/linux/spinlock.h:585 [inline] #1: ffff888021f40d40 (&port->lock#2){-.-.}-{3:3}, at: tty_port_close_start+0x5e/0x580 drivers/tty/tty_port.c:599 #2: ffffffff8df35980 (console_lock){+.+.}-{0:0}, at: _printk+0xcf/0x120 kernel/printk/printk.c:2451 #3: ffffffff8de1d238 (console_srcu){....}-{0:0}, at: rcu_try_lock_acquire include/linux/rcupdate.h:336 [inline] #3: ffffffff8de1d238 (console_srcu){....}-{0:0}, at: srcu_read_lock_nmisafe include/linux/srcu.h:409 [inline] #3: ffffffff8de1d238 (console_srcu){....}-{0:0}, at: console_srcu_read_lock kernel/printk/printk.c:289 [inline] #3: ffffffff8de1d238 (console_srcu){....}-{0:0}, at: console_flush_one_record kernel/printk/printk.c:3192 [inline] #3: ffffffff8de1d238 (console_srcu){....}-{0:0}, at: console_flush_all+0x11a/0xb00 kernel/printk/printk.c:3289 stack backtrace: CPU: 1 UID: 0 PID: 11361 Comm: syz.0.1522 Tainted: G L syzkaller #0 PREEMPT(full) Tainted: [L]=SOFTLOCKUP Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025 Call Trace: dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2043 check_noncircular+0x12e/0x150 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+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237 lock_acquire+0x107/0x340 kernel/locking/lockdep.c:5868 console_lock_spinning_enable kernel/printk/printk.c:1900 [inline] console_emit_next_record kernel/printk/printk.c:3123 [inline] console_flush_one_record kernel/printk/printk.c:3215 [inline] console_flush_all+0x6bc/0xb00 kernel/printk/printk.c:3289 __console_flush_and_unlock kernel/printk/printk.c:3319 [inline] console_unlock+0xbb/0x190 kernel/printk/printk.c:3359 vprintk_emit+0x47b/0x550 kernel/printk/printk.c:2426 _printk+0xcf/0x120 kernel/printk/printk.c:2451 tty_port_close_start+0x3f4/0x580 drivers/tty/tty_port.c:601 tty_port_close+0x2a/0x170 drivers/tty/tty_port.c:682 tty_release+0x389/0x1720 drivers/tty/tty_io.c:1745 __fput+0x44c/0xa70 fs/file_table.c:468 task_work_run+0x1d4/0x260 kernel/task_work.c:233 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline] __exit_to_user_mode_loop kernel/entry/common.c:44 [inline] exit_to_user_mode_loop+0xef/0x4e0 kernel/entry/common.c:75 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline] syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline] syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline] syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline] do_syscall_64+0x2c1/0xf80 arch/x86/entry/syscall_64.c:100 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f276238f749 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f27631df038 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4 RAX: 0000000000000000 RBX: 00007f27625e6360 RCX: 00007f276238f749 RDX: 0000000000000000 RSI: ffffffffffffffff RDI: 0000000000000008 RBP: 00007f2762413f91 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f27625e63f8 R14: 00007f27625e6360 R15: 00007f276270fa28