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possible deadlock in serial8250_handle_irq (2)

Status: upstream: reported on 2026/01/14 22:52
Subsystems: ppp fs
[Documentation on labels]
Reported-by: syzbot+b503105c2410c3433459@syzkaller.appspotmail.com
First crash: 94d, last: 22d
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ID Workflow Result Correct Bug Created Started Finished Revision Error
ea9999bd-ebbe-4869-b311-f0630091f5a4 repro possible deadlock in serial8250_handle_irq (2) 2026/03/07 18:25 2026/03/07 18:25 2026/03/07 18:34 31e9c887f7dc24e04b3ca70d0d54fc34141844b0
Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [fs?] possible deadlock in serial8250_handle_irq (2) 0 (1) 2026/01/14 22:52
Similar bugs (6)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-5.15 possible deadlock in serial8250_handle_irq 4 2 304d 369d 0/3 auto-obsoleted due to no activity on 2025/09/22 18:06
upstream possible deadlock in serial8250_handle_irq hams 4 C 180 196d 997d 29/29 fixed on 2025/10/29 21:02
linux-6.1 possible deadlock in serial8250_handle_irq (2) 4 14 97d 272d 0/3 upstream: reported on 2025/07/16 08:44
linux-6.6 possible deadlock in serial8250_handle_irq 4 2 282d 283d 0/2 auto-obsoleted due to no activity on 2025/10/14 13:08
linux-6.1 possible deadlock in serial8250_handle_irq 4 1 483d 483d 0/3 auto-obsoleted due to no activity on 2025/03/27 21:41
linux-5.15 possible deadlock in serial8250_handle_irq (2) 4 11 22d 188d 0/3 upstream: reported on 2025/10/09 00:28

Sample crash report:
=====================================================
WARNING: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected
syzkaller #0 Tainted: G             L     
-----------------------------------------------------
syz.8.6666/32332 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
ffffffff8fa16298 (disc_data_lock){.+.+}-{3:3}, at: sp_get+0x18/0xf0 drivers/net/ppp/ppp_synctty.c:138

and this task is already holding:
ffffffff9b4a7658 (&port_lock_key){-.-.}-{3:3}, at: uart_port_lock_irqsave include/linux/serial_core.h:717 [inline]
ffffffff9b4a7658 (&port_lock_key){-.-.}-{3:3}, at: uart_port_ref_lock drivers/tty/serial/serial_core.c:83 [inline]
ffffffff9b4a7658 (&port_lock_key){-.-.}-{3:3}, at: uart_carrier_raised+0xfa/0x7c0 drivers/tty/serial/serial_core.c:1876
which would create a new lock dependency:
 (&port_lock_key){-.-.}-{3:3} -> (disc_data_lock){.+.+}-{3:3}

but this new dependency connects a HARDIRQ-irq-safe lock:
 (&port_lock_key){-.-.}-{3:3}

... which became HARDIRQ-irq-safe at:
  lock_acquire kernel/locking/lockdep.c:5868 [inline]
  lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:132 [inline]
  _raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:162
  uart_port_lock_irqsave include/linux/serial_core.h:717 [inline]
  class_uart_port_lock_irqsave_constructor include/linux/serial_core.h:797 [inline]
  serial8250_handle_irq.part.0+0x28/0x550 drivers/tty/serial/8250/8250_port.c:1840
  serial8250_handle_irq drivers/tty/serial/8250/8250_port.c:1837 [inline]
  serial8250_default_handle_irq+0xc2/0x2a0 drivers/tty/serial/8250/8250_port.c:1855
  serial8250_interrupt+0xf8/0x1d0 drivers/tty/serial/8250/8250_core.c:86
  __handle_irq_event_percpu+0x232/0x8e0 kernel/irq/handle.c:209
  handle_irq_event_percpu kernel/irq/handle.c:246 [inline]
  handle_irq_event+0xab/0x1e0 kernel/irq/handle.c:263
  handle_edge_irq+0x375/0x970 kernel/irq/chip.c:855
  generic_handle_irq_desc include/linux/irqdesc.h:186 [inline]
  handle_irq arch/x86/kernel/irq.c:262 [inline]
  call_irq_handler arch/x86/kernel/irq.c:318 [inline]
  __common_interrupt+0xd8/0x2f0 arch/x86/kernel/irq.c:333
  common_interrupt+0xb9/0xe0 arch/x86/kernel/irq.c:326
  asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:688
  native_safe_halt arch/x86/include/asm/irqflags.h:48 [inline]
  pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:62
  arch_safe_halt arch/x86/include/asm/paravirt.h:73 [inline]
  default_idle+0x9/0x10 arch/x86/kernel/process.c:767
  default_idle_call+0x6c/0xb0 kernel/sched/idle.c:122
  cpuidle_idle_call kernel/sched/idle.c:199 [inline]
  do_idle+0x464/0x590 kernel/sched/idle.c:352
  cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:451
  start_secondary+0x21d/0x2d0 arch/x86/kernel/smpboot.c:312
  common_startup_64+0x13e/0x148

to a HARDIRQ-irq-unsafe lock:
 (disc_data_lock){.+.+}-{3:3}

... which became HARDIRQ-irq-unsafe at:
...
  lock_acquire kernel/locking/lockdep.c:5868 [inline]
  lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
  __raw_read_lock include/linux/rwlock_api_smp.h:161 [inline]
  _raw_read_lock+0x5f/0x70 kernel/locking/spinlock.c:228
  sp_get+0x18/0xf0 drivers/net/ppp/ppp_synctty.c:138
  ppp_synctty_ioctl+0x23/0x250 drivers/net/ppp/ppp_synctty.c:278
  tty_ioctl+0x1204/0x1690 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]
  __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
  do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
  entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

 Possible interrupt unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(disc_data_lock);
                               local_irq_disable();
                               lock(&port_lock_key);
                               lock(disc_data_lock);
  <Interrupt>
    lock(&port_lock_key);

 *** DEADLOCK ***

3 locks held by syz.8.6666/32332:
 #0: ffff8880592af1c0 (&tty->legacy_mutex){+.+.}-{4:4}, at: tty_lock_interruptible+0x75/0xe0 drivers/tty/tty_mutex.c:27
 #1: ffffffff9b4a7658 (&port_lock_key){-.-.}-{3:3}, at: uart_port_lock_irqsave include/linux/serial_core.h:717 [inline]
 #1: ffffffff9b4a7658 (&port_lock_key){-.-.}-{3:3}, at: uart_port_ref_lock drivers/tty/serial/serial_core.c:83 [inline]
 #1: ffffffff9b4a7658 (&port_lock_key){-.-.}-{3:3}, at: uart_carrier_raised+0xfa/0x7c0 drivers/tty/serial/serial_core.c:1876
 #2: ffff8880592af0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref+0x21/0x90 drivers/tty/tty_ldisc.c:263

the dependencies between HARDIRQ-irq-safe lock and the holding lock:
-> (&port_lock_key){-.-.}-{3:3} {
   IN-HARDIRQ-W at:
                    lock_acquire kernel/locking/lockdep.c:5868 [inline]
                    lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
                    __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:132 [inline]
                    _raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:162
                    uart_port_lock_irqsave include/linux/serial_core.h:717 [inline]
                    class_uart_port_lock_irqsave_constructor include/linux/serial_core.h:797 [inline]
                    serial8250_handle_irq.part.0+0x28/0x550 drivers/tty/serial/8250/8250_port.c:1840
                    serial8250_handle_irq drivers/tty/serial/8250/8250_port.c:1837 [inline]
                    serial8250_default_handle_irq+0xc2/0x2a0 drivers/tty/serial/8250/8250_port.c:1855
                    serial8250_interrupt+0xf8/0x1d0 drivers/tty/serial/8250/8250_core.c:86
                    __handle_irq_event_percpu+0x232/0x8e0 kernel/irq/handle.c:209
                    handle_irq_event_percpu kernel/irq/handle.c:246 [inline]
                    handle_irq_event+0xab/0x1e0 kernel/irq/handle.c:263
                    handle_edge_irq+0x375/0x970 kernel/irq/chip.c:855
                    generic_handle_irq_desc include/linux/irqdesc.h:186 [inline]
                    handle_irq arch/x86/kernel/irq.c:262 [inline]
                    call_irq_handler arch/x86/kernel/irq.c:318 [inline]
                    __common_interrupt+0xd8/0x2f0 arch/x86/kernel/irq.c:333
                    common_interrupt+0xb9/0xe0 arch/x86/kernel/irq.c:326
                    asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:688
                    native_safe_halt arch/x86/include/asm/irqflags.h:48 [inline]
                    pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:62
                    arch_safe_halt arch/x86/include/asm/paravirt.h:73 [inline]
                    default_idle+0x9/0x10 arch/x86/kernel/process.c:767
                    default_idle_call+0x6c/0xb0 kernel/sched/idle.c:122
                    cpuidle_idle_call kernel/sched/idle.c:199 [inline]
                    do_idle+0x464/0x590 kernel/sched/idle.c:352
                    cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:451
                    start_secondary+0x21d/0x2d0 arch/x86/kernel/smpboot.c:312
                    common_startup_64+0x13e/0x148
   IN-SOFTIRQ-W at:
                    lock_acquire kernel/locking/lockdep.c:5868 [inline]
                    lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
                    __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:132 [inline]
                    _raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:162
                    uart_port_lock_irqsave include/linux/serial_core.h:717 [inline]
                    class_uart_port_lock_irqsave_constructor include/linux/serial_core.h:797 [inline]
                    serial8250_handle_irq.part.0+0x28/0x550 drivers/tty/serial/8250/8250_port.c:1840
                    serial8250_handle_irq drivers/tty/serial/8250/8250_port.c:1837 [inline]
                    serial8250_default_handle_irq+0xc2/0x2a0 drivers/tty/serial/8250/8250_port.c:1855
                    serial8250_interrupt+0xf8/0x1d0 drivers/tty/serial/8250/8250_core.c:86
                    __handle_irq_event_percpu+0x232/0x8e0 kernel/irq/handle.c:209
                    handle_irq_event_percpu kernel/irq/handle.c:246 [inline]
                    handle_irq_event+0xab/0x1e0 kernel/irq/handle.c:263
                    handle_edge_irq+0x375/0x970 kernel/irq/chip.c:855
                    generic_handle_irq_desc include/linux/irqdesc.h:186 [inline]
                    handle_irq arch/x86/kernel/irq.c:262 [inline]
                    call_irq_handler arch/x86/kernel/irq.c:318 [inline]
                    __common_interrupt+0xd8/0x2f0 arch/x86/kernel/irq.c:333
                    common_interrupt+0x60/0xe0 arch/x86/kernel/irq.c:326
                    asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:688
                    variable_ffs arch/x86/include/asm/bitops.h:312 [inline]
                    handle_softirqs+0x1af/0x9e0 kernel/softirq.c:610
                    __do_softirq kernel/softirq.c:656 [inline]
                    invoke_softirq kernel/softirq.c:496 [inline]
                    __irq_exit_rcu+0xef/0x150 kernel/softirq.c:723
                    irq_exit_rcu+0x9/0x30 kernel/softirq.c:739
                    instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline]
                    sysvec_apic_timer_interrupt+0xa3/0xc0 arch/x86/kernel/apic/apic.c:1056
                    asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
                    console_flush_one_record+0xac3/0xe50 kernel/printk/printk.c:3270
                    console_flush_all kernel/printk/printk.c:3343 [inline]
                    __console_flush_and_unlock kernel/printk/printk.c:3373 [inline]
                    console_unlock+0x103/0x260 kernel/printk/printk.c:3413
                    vprintk_emit+0x407/0x6b0 kernel/printk/printk.c:2479
                    _printk+0xcf/0x110 kernel/printk/printk.c:2504
                    kauditd_printk_skb kernel/audit.c:587 [inline]
                    kauditd_hold_skb.cold+0x3f/0x4e kernel/audit.c:622
                    kauditd_send_queue+0x232/0x2e0 kernel/audit.c:807
                    kauditd_thread+0x645/0xb30 kernel/audit.c:931
                    kthread+0x370/0x450 kernel/kthread.c:436
                    ret_from_fork+0x754/0xd80 arch/x86/kernel/process.c:158
                    ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
   INITIAL USE at:
                   lock_acquire kernel/locking/lockdep.c:5868 [inline]
                   lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
                   __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:132 [inline]
                   _raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:162
                   uart_port_lock_irqsave include/linux/serial_core.h:717 [inline]
                   class_uart_port_lock_irqsave_constructor include/linux/serial_core.h:797 [inline]
                   serial8250_do_set_termios+0x330/0x1730 drivers/tty/serial/8250/8250_port.c:2774
                   serial8250_set_termios+0x73/0x90 drivers/tty/serial/8250/8250_port.c:2801
                   uart_set_options+0x316/0x5e0 drivers/tty/serial/serial_core.c:2237
                   serial8250_console_setup+0x189/0x450 drivers/tty/serial/8250/8250_port.c:3420
                   univ8250_console_setup+0x1eb/0x2e0 drivers/tty/serial/8250/8250_core.c:430
                   console_call_setup kernel/printk/printk.c:3882 [inline]
                   console_call_setup kernel/printk/printk.c:3873 [inline]
                   try_enable_preferred_console+0x2fd/0x530 kernel/printk/printk.c:3926
                   register_console+0x350/0xf50 kernel/printk/printk.c:4120
                   univ8250_console_init+0x6f/0x80 drivers/tty/serial/8250/8250_core.c:515
                   console_init+0x423/0x620 kernel/printk/printk.c:4407
                   start_kernel+0x305/0x480 init/main.c:1147
                   x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310
                   x86_64_start_kernel+0x12b/0x130 arch/x86/kernel/head64.c:291
                   common_startup_64+0x13e/0x148
 }
 ... key      at: [<ffffffff9b4a68c0>] port_lock_key+0x0/0x40

the dependencies between the lock to be acquired
 and HARDIRQ-irq-unsafe lock:
-> (disc_data_lock){.+.+}-{3:3} {
   HARDIRQ-ON-R at:
                    lock_acquire kernel/locking/lockdep.c:5868 [inline]
                    lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
                    __raw_read_lock include/linux/rwlock_api_smp.h:161 [inline]
                    _raw_read_lock+0x5f/0x70 kernel/locking/spinlock.c:228
                    sp_get+0x18/0xf0 drivers/net/ppp/ppp_synctty.c:138
                    ppp_synctty_ioctl+0x23/0x250 drivers/net/ppp/ppp_synctty.c:278
                    tty_ioctl+0x1204/0x1690 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]
                    __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
                    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
                    do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
                    entry_SYSCALL_64_after_hwframe+0x77/0x7f
   SOFTIRQ-ON-R at:
                    lock_acquire kernel/locking/lockdep.c:5868 [inline]
                    lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
                    __raw_read_lock include/linux/rwlock_api_smp.h:161 [inline]
                    _raw_read_lock+0x5f/0x70 kernel/locking/spinlock.c:228
                    sp_get+0x18/0xf0 drivers/net/ppp/ppp_synctty.c:138
                    ppp_synctty_ioctl+0x23/0x250 drivers/net/ppp/ppp_synctty.c:278
                    tty_ioctl+0x1204/0x1690 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]
                    __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
                    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
                    do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
                    entry_SYSCALL_64_after_hwframe+0x77/0x7f
   INITIAL USE at:
                   lock_acquire kernel/locking/lockdep.c:5868 [inline]
                   lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
                   __raw_write_lock_irq include/linux/rwlock_api_smp.h:211 [inline]
                   _raw_write_lock_irq+0x36/0x50 kernel/locking/spinlock.c:326
                   ppp_sync_close+0x1c/0x170 drivers/net/ppp/ppp_synctty.c:218
                   tty_ldisc_close+0x114/0x1a0 drivers/tty/tty_ldisc.c:455
                   tty_ldisc_kill+0x8e/0x150 drivers/tty/tty_ldisc.c:613
                   tty_ldisc_release+0x107/0x2f0 drivers/tty/tty_ldisc.c:781
                   tty_release_struct+0x23/0xe0 drivers/tty/tty_io.c:1681
                   tty_release+0xd7a/0x1300 drivers/tty/tty_io.c:1852
                   __fput+0x3ff/0xb40 fs/file_table.c:469
                   task_work_run+0x150/0x240 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:67 [inline]
                   exit_to_user_mode_loop+0x100/0x4a0 kernel/entry/common.c:98
                   __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 include/linux/entry-common.h:325 [inline]
                   do_syscall_64+0x67c/0xf80 arch/x86/entry/syscall_64.c:100
                   entry_SYSCALL_64_after_hwframe+0x77/0x7f
   INITIAL READ USE at:
                        lock_acquire kernel/locking/lockdep.c:5868 [inline]
                        lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
                        __raw_read_lock include/linux/rwlock_api_smp.h:161 [inline]
                        _raw_read_lock+0x5f/0x70 kernel/locking/spinlock.c:228
                        sp_get+0x18/0xf0 drivers/net/ppp/ppp_synctty.c:138
                        ppp_synctty_ioctl+0x23/0x250 drivers/net/ppp/ppp_synctty.c:278
                        tty_ioctl+0x1204/0x1690 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]
                        __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
                        do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
                        do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
                        entry_SYSCALL_64_after_hwframe+0x77/0x7f
 }
 ... key      at: [<ffffffff8fa16298>] disc_data_lock+0x18/0x1120 mkiss.c:-1
 ... acquired at:
   lock_acquire kernel/locking/lockdep.c:5868 [inline]
   lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
   __raw_read_lock include/linux/rwlock_api_smp.h:161 [inline]
   _raw_read_lock+0x5f/0x70 kernel/locking/spinlock.c:228
   sp_get+0x18/0xf0 drivers/net/ppp/ppp_synctty.c:138
   ppp_sync_wakeup+0x18/0xc0 drivers/net/ppp/ppp_synctty.c:345
   tty_wakeup+0xe8/0x120 drivers/tty/tty_io.c:515
   tty_port_default_wakeup+0x47/0x60 drivers/tty/tty_port.c:67
   uart_write_wakeup drivers/tty/serial/serial_core.c:121 [inline]
   uart_handle_cts_change+0x1ea/0x300 drivers/tty/serial/serial_core.c:3400
   serial8250_modem_status+0x281/0x2f0 drivers/tty/serial/8250/8250_port.c:1751
   serial8250_do_get_mctrl+0xbb/0x390 drivers/tty/serial/8250/8250_port.c:1900
   serial8250_get_mctrl+0x5c/0x80 drivers/tty/serial/8250/8250_port.c:1914
   uart_carrier_raised+0x22c/0x7c0 drivers/tty/serial/serial_core.c:1886
   tty_port_carrier_raised drivers/tty/tty_port.c:420 [inline]
   tty_port_block_til_ready+0x470/0x8c0 drivers/tty/tty_port.c:538
   tty_port_open+0x13e/0x270 drivers/tty/tty_port.c:753
   uart_open+0x41/0x60 drivers/tty/serial/serial_core.c:1929
   tty_open+0x3dd/0xfa0 drivers/tty/tty_io.c:2137
   chrdev_open+0x234/0x6a0 fs/char_dev.c:411
   do_dentry_open+0x6d8/0x1660 fs/open.c:949
   vfs_open+0x82/0x3f0 fs/open.c:1081
   do_open fs/namei.c:4671 [inline]
   path_openat+0x208c/0x31a0 fs/namei.c:4830
   do_file_open+0x20e/0x430 fs/namei.c:4859
   do_sys_openat2+0x10d/0x1e0 fs/open.c:1366
   do_sys_open fs/open.c:1372 [inline]
   __do_sys_openat fs/open.c:1388 [inline]
   __se_sys_openat fs/open.c:1383 [inline]
   __x64_sys_openat+0x12d/0x210 fs/open.c:1383
   do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
   do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
   entry_SYSCALL_64_after_hwframe+0x77/0x7f


stack backtrace:
CPU: 0 UID: 0 PID: 32332 Comm: syz.8.6666 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_bad_irq_dependency kernel/locking/lockdep.c:2616 [inline]
 check_irq_usage+0x7aa/0x810 kernel/locking/lockdep.c:2857
 check_prev_add kernel/locking/lockdep.c:3169 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x14cf/0x2630 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
 __raw_read_lock include/linux/rwlock_api_smp.h:161 [inline]
 _raw_read_lock+0x5f/0x70 kernel/locking/spinlock.c:228
 sp_get+0x18/0xf0 drivers/net/ppp/ppp_synctty.c:138
 ppp_sync_wakeup+0x18/0xc0 drivers/net/ppp/ppp_synctty.c:345
 tty_wakeup+0xe8/0x120 drivers/tty/tty_io.c:515
 tty_port_default_wakeup+0x47/0x60 drivers/tty/tty_port.c:67
 uart_write_wakeup drivers/tty/serial/serial_core.c:121 [inline]
 uart_handle_cts_change+0x1ea/0x300 drivers/tty/serial/serial_core.c:3400
 serial8250_modem_status+0x281/0x2f0 drivers/tty/serial/8250/8250_port.c:1751
 serial8250_do_get_mctrl+0xbb/0x390 drivers/tty/serial/8250/8250_port.c:1900
 serial8250_get_mctrl+0x5c/0x80 drivers/tty/serial/8250/8250_port.c:1914
 uart_carrier_raised+0x22c/0x7c0 drivers/tty/serial/serial_core.c:1886
 tty_port_carrier_raised drivers/tty/tty_port.c:420 [inline]
 tty_port_block_til_ready+0x470/0x8c0 drivers/tty/tty_port.c:538
 tty_port_open+0x13e/0x270 drivers/tty/tty_port.c:753
 uart_open+0x41/0x60 drivers/tty/serial/serial_core.c:1929
 tty_open+0x3dd/0xfa0 drivers/tty/tty_io.c:2137
 chrdev_open+0x234/0x6a0 fs/char_dev.c:411
 do_dentry_open+0x6d8/0x1660 fs/open.c:949
 vfs_open+0x82/0x3f0 fs/open.c:1081
 do_open fs/namei.c:4671 [inline]
 path_openat+0x208c/0x31a0 fs/namei.c:4830
 do_file_open+0x20e/0x430 fs/namei.c:4859
 do_sys_openat2+0x10d/0x1e0 fs/open.c:1366
 do_sys_open fs/open.c:1372 [inline]
 __do_sys_openat fs/open.c:1388 [inline]
 __se_sys_openat fs/open.c:1383 [inline]
 __x64_sys_openat+0x12d/0x210 fs/open.c:1383
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb553d9c799
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fb554ce0028 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007fb554015fa0 RCX: 00007fb553d9c799
RDX: 0000000000020040 RSI: 0000200000000140 RDI: 00000000ffffff9c
RBP: 00007fb553e32c99 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb554016038 R14: 00007fb554015fa0 R15: 00007ffd304583e8
 </TASK>

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/03/23 01:20 upstream 8d8bd2a5aa98 5b92003d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in serial8250_handle_irq
2026/01/10 22:41 upstream b6151c4e60e5 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in serial8250_handle_irq
* Struck through repros no longer work on HEAD.