syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.5.404/6547 is trying to acquire lock:
ffff888017479818 (&pool->lock/1){-.-.}-{2:2}, at: __queue_work+0x60d/0xfb0 kernel/workqueue.c:-1

but task is already holding lock:
ffffffff96d56f68 (&port_lock_key){-.-.}-{2:2}, at: serial8250_handle_irq+0x7a/0x6d0 drivers/tty/serial/8250/8250_port.c:1932

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&port_lock_key){-.-.}-{2:2}:
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0xa4/0xf0 kernel/locking/spinlock.c:162
       serial8250_console_write+0x169/0x17a0 drivers/tty/serial/8250/8250_port.c:3432
       call_console_driver kernel/printk/printk.c:1977 [inline]
       console_emit_next_record+0x947/0xc90 kernel/printk/printk.c:2777
       console_flush_all kernel/printk/printk.c:-1 [inline]
       console_unlock+0x223/0x630 kernel/printk/printk.c:2906
       vprintk_emit+0x489/0x680 kernel/printk/printk.c:2303
       _printk+0xcc/0x110 kernel/printk/printk.c:2328
       register_console+0x6c6/0x9c0 kernel/printk/printk.c:3269
       univ8250_console_init+0x41/0x43 drivers/tty/serial/8250/8250_core.c:687
       console_init+0x1bc/0x78e kernel/printk/printk.c:3359
       start_kernel+0x303/0x539 init/main.c:1088
       secondary_startup_64_no_verify+0xcf/0xdb

-> #3 (console_owner){..-.}-{0:0}:
       console_lock_spinning_enable kernel/printk/printk.c:1818 [inline]
       console_emit_next_record+0x84c/0xc90 kernel/printk/printk.c:2774
       console_flush_all kernel/printk/printk.c:-1 [inline]
       console_unlock+0x223/0x630 kernel/printk/printk.c:2906
       vprintk_emit+0x489/0x680 kernel/printk/printk.c:2303
       _printk+0xcc/0x110 kernel/printk/printk.c:2328
       fail_dump lib/fault-inject.c:45 [inline]
       should_fail_ex+0x37a/0x4d0 lib/fault-inject.c:147
       strncpy_from_user+0x32/0x350 lib/strncpy_from_user.c:118
       strncpy_from_user_nofault+0x6d/0x140 mm/maccess.c:186
       bpf_trace_copy_string kernel/bpf/helpers.c:746 [inline]
       bpf_bprintf_prepare+0xba0/0x13d0 kernel/bpf/helpers.c:971
       ____bpf_trace_printk kernel/trace/bpf_trace.c:384 [inline]
       bpf_trace_printk+0xd8/0x190 kernel/trace/bpf_trace.c:374
       0xffffffffa0002911
       bpf_dispatcher_nop_func include/linux/bpf.h:1012 [inline]
       __bpf_prog_run include/linux/filter.h:603 [inline]
       bpf_prog_run include/linux/filter.h:610 [inline]
       __bpf_trace_run kernel/trace/bpf_trace.c:2285 [inline]
       bpf_trace_run2+0x1cd/0x3b0 kernel/trace/bpf_trace.c:2324
       __traceiter_contention_begin+0x74/0xa0 include/trace/events/lock.h:95
       trace_contention_begin+0x142/0x190 include/trace/events/lock.h:95
       __pv_queued_spin_lock_slowpath+0xdc/0x9c0 kernel/locking/qspinlock.c:405
       pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:591 [inline]
       queued_spin_lock_slowpath+0x43/0x50 arch/x86/include/asm/qspinlock.h:51
       queued_spin_lock include/asm-generic/qspinlock.h:114 [inline]
       do_raw_spin_lock+0x217/0x280 kernel/locking/spinlock_debug.c:115
       raw_spin_rq_lock_nested+0xa5/0x140 kernel/sched/core.c:545
       raw_spin_rq_lock kernel/sched/sched.h:1355 [inline]
       rq_lock kernel/sched/sched.h:1645 [inline]
       __schedule+0x2ed/0x40b0 kernel/sched/core.c:6477
       preempt_schedule_irq+0xb1/0x150 kernel/sched/core.c:6873
       irqentry_exit+0x63/0x70 kernel/entry/common.c:439
       asm_sysvec_reschedule_ipi+0x16/0x20 arch/x86/include/asm/idtentry.h:696
       preempt_count arch/x86/include/asm/preempt.h:27 [inline]
       check_kcov_mode kernel/kcov.c:182 [inline]
       __sanitizer_cov_trace_pc+0x13/0x60 kernel/kcov.c:216
       build_open_flags+0x20d/0x5e0 fs/open.c:1171
       do_sys_openat2+0x9f/0x490 fs/open.c:1308
       do_sys_open fs/open.c:1336 [inline]
       __do_sys_openat fs/open.c:1352 [inline]
       __se_sys_openat fs/open.c:1347 [inline]
       __x64_sys_openat+0x135/0x160 fs/open.c:1347
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #2 (&rq->__lock){-.-.}-{2:2}:
       _raw_spin_lock_nested+0x2e/0x40 kernel/locking/spinlock.c:378
       raw_spin_rq_lock_nested+0x26/0x140 kernel/sched/core.c:537
       raw_spin_rq_lock kernel/sched/sched.h:1355 [inline]
       rq_lock kernel/sched/sched.h:1645 [inline]
       task_fork_fair+0x5c/0x350 kernel/sched/fair.c:11901
       sched_cgroup_fork+0x32c/0x3c0 kernel/sched/core.c:4685
       copy_process+0x24b8/0x4020 kernel/fork.c:2459
       kernel_clone+0x225/0x8b0 kernel/fork.c:2757
       user_mode_thread+0xda/0x130 kernel/fork.c:2833
       rest_init+0x23/0x300 init/main.c:710
       start_kernel+0x0/0x539 init/main.c:905
       start_kernel+0x490/0x539 init/main.c:1152
       secondary_startup_64_no_verify+0xcf/0xdb

-> #1 (&p->pi_lock){-.-.}-{2:2}:
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0xa4/0xf0 kernel/locking/spinlock.c:162
       try_to_wake_up+0x5c/0x1080 kernel/sched/core.c:4111
       create_worker+0x4c3/0x630 kernel/workqueue.c:1967
       workqueue_init+0x4da/0x58a kernel/workqueue.c:6133
       kernel_init_freeable+0x39c/0x5ac init/main.c:1621
       kernel_init+0x19/0x1b0 init/main.c:1526
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

-> #0 (&pool->lock/1){-.-.}-{2:2}:
       check_prev_add kernel/locking/lockdep.c:3090 [inline]
       check_prevs_add kernel/locking/lockdep.c:3209 [inline]
       validate_chain kernel/locking/lockdep.c:3825 [inline]
       __lock_acquire+0x2cf8/0x7c50 kernel/locking/lockdep.c:5049
       lock_acquire+0x1b4/0x490 kernel/locking/lockdep.c:5662
       __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
       _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:154
       __queue_work+0x60d/0xfb0 kernel/workqueue.c:-1
       queue_work_on+0x11d/0x1d0 kernel/workqueue.c:1548
       serial8250_rx_chars drivers/tty/serial/8250/8250_port.c:1801 [inline]
       serial8250_handle_irq+0x456/0x6d0 drivers/tty/serial/8250/8250_port.c:1956
       serial8250_default_handle_irq+0xb4/0x1a0 drivers/tty/serial/8250/8250_port.c:1981
       serial8250_interrupt+0x9b/0x1c0 drivers/tty/serial/8250/8250_core.c:126
       __handle_irq_event_percpu+0x298/0xa30 kernel/irq/handle.c:158
       handle_irq_event_percpu kernel/irq/handle.c:193 [inline]
       handle_irq_event+0x87/0x1e0 kernel/irq/handle.c:210
       handle_edge_irq+0x243/0xb20 kernel/irq/chip.c:819
       generic_handle_irq_desc include/linux/irqdesc.h:158 [inline]
       handle_irq arch/x86/kernel/irq.c:233 [inline]
       __common_interrupt+0xd7/0x1e0 arch/x86/kernel/irq.c:252
       common_interrupt+0x59/0xd0 arch/x86/kernel/irq.c:242
       asm_common_interrupt+0x22/0x40 arch/x86/include/asm/idtentry.h:682
       native_irq_enable arch/x86/include/asm/irqflags.h:-1 [inline]
       arch_local_irq_enable arch/x86/include/asm/irqflags.h:80 [inline]
       handle_softirqs+0x1c8/0x920 kernel/softirq.c:580
       __do_softirq kernel/softirq.c:630 [inline]
       invoke_softirq kernel/softirq.c:470 [inline]
       __irq_exit_rcu+0x12f/0x220 kernel/softirq.c:679
       irq_exit_rcu+0x5/0x20 kernel/softirq.c:691
       instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1118 [inline]
       sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1118
       asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
       __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
       _raw_spin_unlock_irqrestore+0xa5/0x100 kernel/locking/spinlock.c:194
       try_to_wake_up+0x64c/0x1080 kernel/sched/core.c:4229
       wake_up_process kernel/sched/core.c:4361 [inline]
       wake_up_q+0x78/0xc0 kernel/sched/core.c:1009
       futex_wake+0x409/0x4b0 kernel/futex/waitwake.c:184
       do_futex+0x2e2/0x320 kernel/futex/syscalls.c:139
       __do_sys_futex kernel/futex/syscalls.c:211 [inline]
       __se_sys_futex+0x14a/0x440 kernel/futex/syscalls.c:192
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

other info that might help us debug this:

Chain exists of:
  &pool->lock/1 --> console_owner --> &port_lock_key

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&port_lock_key);
                               lock(console_owner);
                               lock(&port_lock_key);
  lock(&pool->lock/1);

 *** DEADLOCK ***

3 locks held by syz.5.404/6547:
 #0: ffff88807e757e30 (&i->lock){-.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
 #0: ffff88807e757e30 (&i->lock){-.-.}-{2:2}, at: serial8250_interrupt+0x3e/0x1c0 drivers/tty/serial/8250/8250_core.c:116
 #1: ffffffff96d56f68 (&port_lock_key){-.-.}-{2:2}, at: serial8250_handle_irq+0x7a/0x6d0 drivers/tty/serial/8250/8250_port.c:1932
 #2: ffffffff8c92b120 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
 #2: ffffffff8c92b120 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:791 [inline]
 #2: ffffffff8c92b120 (rcu_read_lock){....}-{1:2}, at: __queue_work+0xeb/0xfb0 kernel/workqueue.c:1443

stack backtrace:
CPU: 0 PID: 6547 Comm: syz.5.404 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <IRQ>
 dump_stack_lvl+0x168/0x22e lib/dump_stack.c:106
 check_noncircular+0x274/0x310 kernel/locking/lockdep.c:2170
 check_prev_add kernel/locking/lockdep.c:3090 [inline]
 check_prevs_add kernel/locking/lockdep.c:3209 [inline]
 validate_chain kernel/locking/lockdep.c:3825 [inline]
 __lock_acquire+0x2cf8/0x7c50 kernel/locking/lockdep.c:5049
 lock_acquire+0x1b4/0x490 kernel/locking/lockdep.c:5662
 __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
 _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:154
 __queue_work+0x60d/0xfb0 kernel/workqueue.c:-1
 queue_work_on+0x11d/0x1d0 kernel/workqueue.c:1548
 serial8250_rx_chars drivers/tty/serial/8250/8250_port.c:1801 [inline]
 serial8250_handle_irq+0x456/0x6d0 drivers/tty/serial/8250/8250_port.c:1956
 serial8250_default_handle_irq+0xb4/0x1a0 drivers/tty/serial/8250/8250_port.c:1981
 serial8250_interrupt+0x9b/0x1c0 drivers/tty/serial/8250/8250_core.c:126
 __handle_irq_event_percpu+0x298/0xa30 kernel/irq/handle.c:158
 handle_irq_event_percpu kernel/irq/handle.c:193 [inline]
 handle_irq_event+0x87/0x1e0 kernel/irq/handle.c:210
 handle_edge_irq+0x243/0xb20 kernel/irq/chip.c:819
 generic_handle_irq_desc include/linux/irqdesc.h:158 [inline]
 handle_irq arch/x86/kernel/irq.c:233 [inline]
 __common_interrupt+0xd7/0x1e0 arch/x86/kernel/irq.c:252
 common_interrupt+0x59/0xd0 arch/x86/kernel/irq.c:242
 asm_common_interrupt+0x22/0x40 arch/x86/include/asm/idtentry.h:682
RIP: 0010:variable_ffs arch/x86/include/asm/bitops.h:319 [inline]
RIP: 0010:handle_softirqs+0x1c8/0x920 kernel/softirq.c:584
Code: 89 7c 24 44 0f b7 db 48 c7 c7 00 fc 6a 8a e8 7f 06 c2 08 65 66 c7 05 65 24 b5 7e 00 00 e8 00 c0 38 00 fb 49 c7 c6 c0 a0 60 8c <89> 5c 24 4c b8 ff ff ff ff 0f bc 44 24 4c 41 89 c5 41 ff c5 0f 84
RSP: 0018:ffffc90000007e00 EFLAGS: 00000286
RAX: 18764b9b1830f400 RBX: 0000000000000100 RCX: 18764b9b1830f400
RDX: dffffc0000000000 RSI: ffffffff8a6c0600 RDI: ffffffff8abef920
RBP: ffffc90000007f30 R08: ffffffff8f7dd008 R09: ffffffff8f7dd018
R10: ffffffff8f7dd010 R11: ffffffff8f7dd003 R12: dffffc0000000000
R13: 0000000000000000 R14: ffffffff8c60a0c0 R15: 000000000000000a
 __do_softirq kernel/softirq.c:630 [inline]
 invoke_softirq kernel/softirq.c:470 [inline]
 __irq_exit_rcu+0x12f/0x220 kernel/softirq.c:679
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:691
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1118 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1118
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xa5/0x100 kernel/locking/spinlock.c:194
Code: 74 05 e8 6e be 6c f7 48 c7 44 24 20 00 00 00 00 9c 8f 44 24 20 f6 44 24 21 02 75 4b f7 c3 00 02 00 00 74 01 fb bf 01 00 00 00 <e8> 16 44 3d f7 65 8b 05 a7 f1 e7 75 85 c0 74 3c 48 c7 04 24 0e 36
RSP: 0018:ffffc90003f07ac0 EFLAGS: 00000206
RAX: 18764b9b1830f400 RBX: 0000000000000a02 RCX: 18764b9b1830f400
RDX: dffffc0000000000 RSI: ffffffff8a6c0600 RDI: 0000000000000001
RBP: ffffc90003f07b48 R08: dffffc0000000000 R09: ffffed1005c6b141
R10: ffffed1005c6b141 R11: 1ffff11005c6b140 R12: dffffc0000000000
R13: dffffc0000000000 R14: ffff88802e358a00 R15: 1ffff920007e0f58
 try_to_wake_up+0x64c/0x1080 kernel/sched/core.c:4229
 wake_up_process kernel/sched/core.c:4361 [inline]
 wake_up_q+0x78/0xc0 kernel/sched/core.c:1009
 futex_wake+0x409/0x4b0 kernel/futex/waitwake.c:184
 do_futex+0x2e2/0x320 kernel/futex/syscalls.c:139
 __do_sys_futex kernel/futex/syscalls.c:211 [inline]
 __se_sys_futex+0x14a/0x440 kernel/futex/syscalls.c:192
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f1d7ab8f749
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:00007f1d7bb120e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: ffffffffffffffda RBX: 00007f1d7ade5fa8 RCX: 00007f1d7ab8f749
RDX: 00000000000f4240 RSI: 0000000000000081 RDI: 00007f1d7ade5fac
RBP: 00007f1d7ade5fa0 R08: 00184d19035437f2 R09: 0000000000000000
R10: 000000000000000a R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1d7ade6038 R14: 00007ffeaee5fd70 R15: 00007ffeaee5fe58
 </TASK>
----------------
Code disassembly (best guess):
   0:	89 7c 24 44          	mov    %edi,0x44(%rsp)
   4:	0f b7 db             	movzwl %bx,%ebx
   7:	48 c7 c7 00 fc 6a 8a 	mov    $0xffffffff8a6afc00,%rdi
   e:	e8 7f 06 c2 08       	call   0x8c20692
  13:	65 66 c7 05 65 24 b5 	movw   $0x0,%gs:0x7eb52465(%rip)        # 0x7eb52482
  1a:	7e 00 00
  1d:	e8 00 c0 38 00       	call   0x38c022
  22:	fb                   	sti
  23:	49 c7 c6 c0 a0 60 8c 	mov    $0xffffffff8c60a0c0,%r14
* 2a:	89 5c 24 4c          	mov    %ebx,0x4c(%rsp) <-- trapping instruction
  2e:	b8 ff ff ff ff       	mov    $0xffffffff,%eax
  33:	0f bc 44 24 4c       	bsf    0x4c(%rsp),%eax
  38:	41 89 c5             	mov    %eax,%r13d
  3b:	41 ff c5             	inc    %r13d
  3e:	0f                   	.byte 0xf
  3f:	84                   	.byte 0x84