syzbot

------------[ cut here ]------------
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
migration/0/19 is trying to acquire lock:
ffffffff8e2d6740 (console_owner){....}-{0:0}, at: console_lock_spinning_enable+0x61/0x80 kernel/printk/printk.c:1900

but task is already holding lock:
ffff8880b843acd8 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested kernel/sched/core.c:647 [inline]
ffff8880b843acd8 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x7e/0x130 kernel/sched/core.c:632

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&rq->__lock){-.-.}-{2:2}:
       _raw_spin_lock_nested+0x31/0x40 kernel/locking/spinlock.c:378
       raw_spin_rq_lock_nested+0x29/0x130 kernel/sched/core.c:639
       raw_spin_rq_lock kernel/sched/sched.h:1558 [inline]
       task_rq_lock+0xcf/0x490 kernel/sched/core.c:739
       cgroup_move_task+0x81/0x2a0 kernel/sched/psi.c:1170
       css_set_move_task+0x288/0x5f0 kernel/cgroup/cgroup.c:951
       cgroup_post_fork+0x201/0x9e0 kernel/cgroup/cgroup.c:6912
       copy_process+0x51d3/0x74e0 kernel/fork.c:2422
       kernel_clone+0xfc/0x910 kernel/fork.c:2608
       user_mode_thread+0xc8/0x110 kernel/fork.c:2684
       rest_init+0x23/0x2b0 init/main.c:722
       start_kernel+0x3f6/0x4d0 init/main.c:1111
       x86_64_start_reservations+0x18/0x30 arch/x86/kernel/head64.c:310
       x86_64_start_kernel+0x130/0x190 arch/x86/kernel/head64.c:291
       common_startup_64+0x13e/0x148

-> #3 (&p->pi_lock){-.-.}-{2:2}:
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:162
       class_raw_spinlock_irqsave_constructor include/linux/spinlock.h:557 [inline]
       try_to_wake_up+0xb7/0x1860 kernel/sched/core.c:4106
       __wake_up_common+0x135/0x1f0 kernel/sched/wait.c:108
       __wake_up_common_lock kernel/sched/wait.c:125 [inline]
       __wake_up+0x31/0x60 kernel/sched/wait.c:146
       tty_port_default_wakeup+0x4d/0x60 drivers/tty/tty_port.c:67
       serial8250_tx_chars+0x68e/0x860 drivers/tty/serial/8250/8250_port.c:1719
       serial8250_handle_irq+0x761/0xcb0 drivers/tty/serial/8250/8250_port.c:1827
       serial8250_default_handle_irq+0x9e/0x270 drivers/tty/serial/8250/8250_port.c:1846
       serial8250_interrupt+0xf8/0x1d0 drivers/tty/serial/8250/8250_core.c:82
       __handle_irq_event_percpu+0x236/0x890 kernel/irq/handle.c:211
       handle_irq_event_percpu kernel/irq/handle.c:248 [inline]
       handle_irq_event+0xab/0x1e0 kernel/irq/handle.c:265
       handle_edge_irq+0x3ca/0x9e0 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:311 [inline]
       __common_interrupt+0xd0/0x2f0 arch/x86/kernel/irq.c:326
       common_interrupt+0xba/0xe0 arch/x86/kernel/irq.c:319
       asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:688
       get_current arch/x86/include/asm/current.h:25 [inline]
       finish_task_switch.isra.0+0x210/0xbd0 kernel/sched/core.c:5114
       context_switch kernel/sched/core.c:5259 [inline]
       __schedule+0x1141/0x6150 kernel/sched/core.c:6863
       __schedule_loop kernel/sched/core.c:6945 [inline]
       schedule+0xe7/0x3a0 kernel/sched/core.c:6960
       worker_thread+0x2e5/0xf10 kernel/workqueue.c:3436
       kthread+0x3c5/0x780 kernel/kthread.c:463
       ret_from_fork+0x983/0xb10 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

-> #2 (&tty->write_wait){-.-.}-{3:3}:
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:162
       __wake_up_common_lock kernel/sched/wait.c:124 [inline]
       __wake_up+0x1c/0x60 kernel/sched/wait.c:146
       tty_port_default_wakeup+0x4d/0x60 drivers/tty/tty_port.c:67
       serial8250_tx_chars+0x68e/0x860 drivers/tty/serial/8250/8250_port.c:1719
       serial8250_handle_irq+0x761/0xcb0 drivers/tty/serial/8250/8250_port.c:1827
       serial8250_default_handle_irq+0x9e/0x270 drivers/tty/serial/8250/8250_port.c:1846
       serial8250_interrupt+0xf8/0x1d0 drivers/tty/serial/8250/8250_core.c:82
       __handle_irq_event_percpu+0x236/0x890 kernel/irq/handle.c:211
       handle_irq_event_percpu kernel/irq/handle.c:248 [inline]
       handle_irq_event+0xab/0x1e0 kernel/irq/handle.c:265
       handle_edge_irq+0x3ca/0x9e0 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:311 [inline]
       __common_interrupt+0xd0/0x2f0 arch/x86/kernel/irq.c:326
       common_interrupt+0xba/0xe0 arch/x86/kernel/irq.c:319
       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:81
       arch_safe_halt arch/x86/include/asm/paravirt.h:107 [inline]
       default_idle+0x13/0x20 arch/x86/kernel/process.c:767
       default_idle_call+0x6c/0xb0 kernel/sched/idle.c:122
       cpuidle_idle_call kernel/sched/idle.c:191 [inline]
       do_idle+0x38d/0x510 kernel/sched/idle.c:332
       cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:430
       rest_init+0x16b/0x2b0 init/main.c:757
       start_kernel+0x3f6/0x4d0 init/main.c:1111
       x86_64_start_reservations+0x18/0x30 arch/x86/kernel/head64.c:310
       x86_64_start_kernel+0x130/0x190 arch/x86/kernel/head64.c:291
       common_startup_64+0x13e/0x148

-> #1 (&port_lock_key){-.-.}-{3:3}:
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:162
       uart_port_lock_irqsave include/linux/serial_core.h:717 [inline]
       serial8250_console_write+0x181/0x1890 drivers/tty/serial/8250/8250_port.c:3301
       console_emit_next_record kernel/printk/printk.c:3129 [inline]
       console_flush_one_record+0x796/0xc60 kernel/printk/printk.c:3215
       console_flush_all kernel/printk/printk.c:3289 [inline]
       __console_flush_and_unlock kernel/printk/printk.c:3319 [inline]
       console_unlock+0xef/0x240 kernel/printk/printk.c:3359
       vprintk_emit+0x407/0x6b0 kernel/printk/printk.c:2426
       _printk+0xc7/0x100 kernel/printk/printk.c:2451
       register_console+0x823/0x1210 kernel/printk/printk.c:4165
       univ8250_console_init+0x5f/0x90 drivers/tty/serial/8250/8250_core.c:511
       console_init+0x152/0x600 kernel/printk/printk.c:4364
       start_kernel+0x29f/0x4d0 init/main.c:1048
       x86_64_start_reservations+0x18/0x30 arch/x86/kernel/head64.c:310
       x86_64_start_kernel+0x130/0x190 arch/x86/kernel/head64.c:291
       common_startup_64+0x13e/0x148

-> #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+0x1542/0x22f0 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x179/0x330 kernel/locking/lockdep.c:5825
       console_lock_spinning_enable+0x72/0x80 kernel/printk/printk.c:1900
       console_emit_next_record kernel/printk/printk.c:3123 [inline]
       console_flush_one_record+0x73f/0xc60 kernel/printk/printk.c:3215
       console_flush_all kernel/printk/printk.c:3289 [inline]
       __console_flush_and_unlock kernel/printk/printk.c:3319 [inline]
       console_unlock+0xef/0x240 kernel/printk/printk.c:3359
       vprintk_emit+0x407/0x6b0 kernel/printk/printk.c:2426
       _printk+0xc7/0x100 kernel/printk/printk.c:2451
       __report_bug+0x3a6/0x520 lib/bug.c:239
       report_bug+0xb2/0x220 lib/bug.c:277
       handle_bug+0x127/0x260 arch/x86/kernel/traps.c:435
       exc_invalid_op+0x17/0x50 arch/x86/kernel/traps.c:489
       asm_exc_invalid_op+0x1a/0x20 arch/x86/include/asm/idtentry.h:616
       lockdep_assert_rq_held kernel/sched/sched.h:1549 [inline]
       lockdep_assert_rq_held kernel/sched/sched.h:1547 [inline]
       update_rq_clock+0x34a/0xc70 kernel/sched/core.c:837
       pick_next_task kernel/sched/core.c:6088 [inline]
       __schedule+0x212d/0x6150 kernel/sched/core.c:6805
       __schedule_loop kernel/sched/core.c:6945 [inline]
       schedule+0xe7/0x3a0 kernel/sched/core.c:6960
       smpboot_thread_fn+0x8e6/0xae0 kernel/smpboot.c:156
       kthread+0x3c5/0x780 kernel/kthread.c:463
       ret_from_fork+0x983/0xb10 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

other info that might help us debug this:

Chain exists of:
  console_owner --> &p->pi_lock --> &rq->__lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&rq->__lock);
                               lock(&p->pi_lock);
                               lock(&rq->__lock);
  lock(console_owner);

 *** DEADLOCK ***

3 locks held by migration/0/19:
 #0: ffff8880b843acd8 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested kernel/sched/core.c:647 [inline]
 #0: ffff8880b843acd8 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x7e/0x130 kernel/sched/core.c:632
 #1: ffffffff8e3b6b80 (console_lock){+.+.}-{0:0}, at: _printk+0xc7/0x100 kernel/printk/printk.c:2451
 #2: ffffffff8e3b6bf8 (console_srcu){....}-{0:0}, at: rcu_try_lock_acquire include/linux/rcupdate.h:336 [inline]
 #2: ffffffff8e3b6bf8 (console_srcu){....}-{0:0}, at: srcu_read_lock_nmisafe include/linux/srcu.h:409 [inline]
 #2: ffffffff8e3b6bf8 (console_srcu){....}-{0:0}, at: console_srcu_read_lock kernel/printk/printk.c:289 [inline]
 #2: ffffffff8e3b6bf8 (console_srcu){....}-{0:0}, at: console_flush_one_record+0x103/0xc60 kernel/printk/printk.c:3192

stack backtrace:
CPU: 0 UID: 0 PID: 19 Comm: migration/0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Stopper: 0x0 <- 0x0
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x2db/0x410 kernel/locking/lockdep.c:2043
 check_noncircular+0x146/0x160 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+0x1542/0x22f0 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x179/0x330 kernel/locking/lockdep.c:5825
 console_lock_spinning_enable+0x72/0x80 kernel/printk/printk.c:1900
 console_emit_next_record kernel/printk/printk.c:3123 [inline]
 console_flush_one_record+0x73f/0xc60 kernel/printk/printk.c:3215
 console_flush_all kernel/printk/printk.c:3289 [inline]
 __console_flush_and_unlock kernel/printk/printk.c:3319 [inline]
 console_unlock+0xef/0x240 kernel/printk/printk.c:3359
 vprintk_emit+0x407/0x6b0 kernel/printk/printk.c:2426
 _printk+0xc7/0x100 kernel/printk/printk.c:2451
 __report_bug+0x3a6/0x520 lib/bug.c:239
 report_bug+0xb2/0x220 lib/bug.c:277
 handle_bug+0x127/0x260 arch/x86/kernel/traps.c:435
 exc_invalid_op+0x17/0x50 arch/x86/kernel/traps.c:489
 asm_exc_invalid_op+0x1a/0x20 arch/x86/include/asm/idtentry.h:616
RIP: 0010:lockdep_assert_rq_held kernel/sched/sched.h:1549 [inline]
RIP: 0010:lockdep_assert_rq_held kernel/sched/sched.h:1547 [inline]
RIP: 0010:update_rq_clock+0x34a/0xc70 kernel/sched/core.c:837
Code: ab 48 0b 00 00 48 83 c4 18 5b 5d 41 5c 41 5d 41 5e 41 5f e9 98 6b dc 09 a8 04 0f 84 9c fd ff ff 90 0f 0b 90 e9 93 fd ff ff 90 <0f> 0b 90 e9 4f fd ff ff 48 8d bb 18 0e 00 00 48 b8 00 00 00 00 00
RSP: 0000:ffffc90000187bd0 EFLAGS: 00010046
RAX: 0000000000000000 RBX: ffff8880b853acc0 RCX: 0000000000000001
RDX: 0000000000000000 RSI: ffffffff8da94318 RDI: ffffffff8bf21680
RBP: 0000000000000001 R08: ffff8880b843b7c8 R09: ffffed100f4fbc00
R10: ffff88807a7de007 R11: 0000000000000001 R12: ffffffff90878854
R13: ffffffff8dd53560 R14: ffff88802d845b80 R15: ffff8880b853acc0
 pick_next_task kernel/sched/core.c:6088 [inline]
 __schedule+0x212d/0x6150 kernel/sched/core.c:6805
 __schedule_loop kernel/sched/core.c:6945 [inline]
 schedule+0xe7/0x3a0 kernel/sched/core.c:6960
 smpboot_thread_fn+0x8e6/0xae0 kernel/smpboot.c:156
 kthread+0x3c5/0x780 kernel/kthread.c:463
 ret_from_fork+0x983/0xb10 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>
WARNING: kernel/sched/sched.h:1549 at lockdep_assert_rq_held kernel/sched/sched.h:1549 [inline], CPU#0: migration/0/19
WARNING: kernel/sched/sched.h:1549 at lockdep_assert_rq_held kernel/sched/sched.h:1547 [inline], CPU#0: migration/0/19
WARNING: kernel/sched/sched.h:1549 at update_rq_clock+0x34a/0xc70 kernel/sched/core.c:837, CPU#0: migration/0/19
Modules linked in:
CPU: 0 UID: 0 PID: 19 Comm: migration/0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Stopper: 0x0 <- 0x0
RIP: 0010:lockdep_assert_rq_held kernel/sched/sched.h:1549 [inline]
RIP: 0010:lockdep_assert_rq_held kernel/sched/sched.h:1547 [inline]
RIP: 0010:update_rq_clock+0x34a/0xc70 kernel/sched/core.c:837
Code: ab 48 0b 00 00 48 83 c4 18 5b 5d 41 5c 41 5d 41 5e 41 5f e9 98 6b dc 09 a8 04 0f 84 9c fd ff ff 90 0f 0b 90 e9 93 fd ff ff 90 <0f> 0b 90 e9 4f fd ff ff 48 8d bb 18 0e 00 00 48 b8 00 00 00 00 00
RSP: 0000:ffffc90000187bd0 EFLAGS: 00010046
RAX: 0000000000000000 RBX: ffff8880b853acc0 RCX: 0000000000000001
RDX: 0000000000000000 RSI: ffffffff8da94318 RDI: ffffffff8bf21680
RBP: 0000000000000001 R08: ffff8880b843b7c8 R09: ffffed100f4fbc00
R10: ffff88807a7de007 R11: 0000000000000001 R12: ffffffff90878854
R13: ffffffff8dd53560 R14: ffff88802d845b80 R15: ffff8880b853acc0
FS:  0000000000000000(0000) GS:ffff888124965000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f5269915690 CR3: 00000000756fa000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 pick_next_task kernel/sched/core.c:6088 [inline]
 __schedule+0x212d/0x6150 kernel/sched/core.c:6805
 __schedule_loop kernel/sched/core.c:6945 [inline]
 schedule+0xe7/0x3a0 kernel/sched/core.c:6960
 smpboot_thread_fn+0x8e6/0xae0 kernel/smpboot.c:156
 kthread+0x3c5/0x780 kernel/kthread.c:463
 ret_from_fork+0x983/0xb10 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>