syzbot

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WARNING: possible circular locking dependency detected
6.16.0-rc1-syzkaller-g39dfc971e42d #0 Not tainted
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bch-copygc/loop/7881 is trying to acquire lock:
ffff0000c9cb46c8 (&p->pi_lock){-.-.}-{2:2}, at: class_raw_spinlock_irqsave_constructor include/linux/spinlock.h:557 [inline]
ffff0000c9cb46c8 (&p->pi_lock){-.-.}-{2:2}, at: try_to_wake_up+0x68/0xdf0 kernel/sched/core.c:4226

but task is already holding lock:
ffff8000975fb610 (&obj_hash[i].lock){-.-.}-{2:2}, at: __debug_object_init+0x6c/0x40c lib/debugobjects.c:741

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&obj_hash[i].lock){-.-.}-{2:2}:
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0x5c/0x7c kernel/locking/spinlock.c:162
       debug_object_assert_init+0xa0/0x2c8 lib/debugobjects.c:1007
       debug_timer_assert_init kernel/time/timer.c:803 [inline]
       debug_assert_init kernel/time/timer.c:848 [inline]
       __mod_timer+0x5c/0xd00 kernel/time/timer.c:1025
       add_timer_global+0x88/0xc0 kernel/time/timer.c:1283
       __queue_delayed_work+0x218/0x2c8 kernel/workqueue.c:2526
       queue_delayed_work_on+0xe4/0x194 kernel/workqueue.c:2561
       queue_delayed_work include/linux/workqueue.h:677 [inline]
       schedule_delayed_work include/linux/workqueue.h:817 [inline]
       psi_group_change+0xd50/0x12e4 kernel/sched/psi.c:873
       psi_task_change+0xec/0x244 kernel/sched/psi.c:912
       psi_enqueue kernel/sched/stats.h:166 [inline]
       enqueue_task+0x250/0x2f4 kernel/sched/core.c:2086
       activate_task kernel/sched/core.c:2126 [inline]
       wake_up_new_task+0x324/0x990 kernel/sched/core.c:4891
       kernel_clone+0x440/0x7a0 kernel/fork.c:2630
       user_mode_thread+0xc8/0x11c kernel/fork.c:2677
       rest_init+0x30/0x2f4 init/main.c:709
       start_kernel+0x450/0x4ac init/main.c:1101
       __primary_switched+0x8c/0x94 arch/arm64/kernel/head.S:246

-> #1 (&rq->__lock){-.-.}-{2:2}:
       _raw_spin_lock_nested+0x50/0x6c kernel/locking/spinlock.c:378
       raw_spin_rq_lock_nested kernel/sched/core.c:606 [inline]
       raw_spin_rq_lock kernel/sched/sched.h:1532 [inline]
       task_rq_lock+0xc4/0x33c kernel/sched/core.c:708
       cgroup_move_task+0x9c/0x454 kernel/sched/psi.c:1161
       css_set_move_task+0x69c/0x8bc kernel/cgroup/cgroup.c:918
       cgroup_post_fork+0x160/0x5cc kernel/cgroup/cgroup.c:6754
       copy_process+0x2e48/0x31ec kernel/fork.c:2413
       kernel_clone+0x1d8/0x7a0 kernel/fork.c:2599
       user_mode_thread+0xc8/0x11c kernel/fork.c:2677
       rest_init+0x30/0x2f4 init/main.c:709
       start_kernel+0x450/0x4ac init/main.c:1101
       __primary_switched+0x8c/0x94 arch/arm64/kernel/head.S:246

-> #0 (&p->pi_lock){-.-.}-{2:2}:
       check_prev_add kernel/locking/lockdep.c:3168 [inline]
       check_prevs_add kernel/locking/lockdep.c:3287 [inline]
       validate_chain kernel/locking/lockdep.c:3911 [inline]
       __lock_acquire+0x1774/0x30a4 kernel/locking/lockdep.c:5240
       lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5871
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0x5c/0x7c kernel/locking/spinlock.c:162
       class_raw_spinlock_irqsave_constructor include/linux/spinlock.h:557 [inline]
       try_to_wake_up+0x68/0xdf0 kernel/sched/core.c:4226
       wake_up_process kernel/sched/core.c:4475 [inline]
       wake_up_q+0x70/0x9c kernel/sched/core.c:1081
       up+0x100/0x170 kernel/locking/semaphore.c:235
       __up_console_sem kernel/printk/printk.c:343 [inline]
       __console_unlock+0x88/0xc4 kernel/printk/printk.c:2885
       __console_flush_and_unlock kernel/printk/printk.c:3287 [inline]
       console_unlock+0xfc/0x288 kernel/printk/printk.c:3325
       vprintk_emit+0x298/0x430 kernel/printk/printk.c:2450
       vprintk_default+0x54/0x80 kernel/printk/printk.c:2465
       vprintk+0x90/0x128 kernel/printk/printk_safe.c:82
       _printk+0xd0/0x118 kernel/printk/printk.c:2475
       __report_bug lib/bug.c:191 [inline]
       report_bug+0x3a8/0x568 lib/bug.c:215
       bug_handler+0x50/0x1fc arch/arm64/kernel/traps.c:1002
       call_break_hook arch/arm64/kernel/debug-monitors.c:315 [inline]
       brk_handler+0x1d8/0x288 arch/arm64/kernel/debug-monitors.c:325
       do_debug_exception+0x1e4/0x38c arch/arm64/mm/fault.c:1002
       el1_dbg+0x64/0x80 arch/arm64/kernel/entry-common.c:513
       el1h_64_sync_handler+0x40/0xcc arch/arm64/kernel/entry-common.c:559
       el1h_64_sync+0x6c/0x70 arch/arm64/kernel/entry.S:595
       debug_object_is_on_stack lib/debugobjects.c:-1 [inline]
       lookup_object_or_alloc lib/debugobjects.c:688 [inline]
       __debug_object_init+0x364/0x40c lib/debugobjects.c:743
       debug_object_init+0x20/0x2c lib/debugobjects.c:779
       __init_work+0x58/0x68 kernel/workqueue.c:677
       rhashtable_init_noprof+0x734/0xa10 lib/rhashtable.c:1085
       bch2_copygc_thread+0xec/0xd40 fs/bcachefs/movinggc.c:353
       kthread+0x5fc/0x75c kernel/kthread.c:464
       ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:847

other info that might help us debug this:

Chain exists of:
  &p->pi_lock --> &rq->__lock --> &obj_hash[i].lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&obj_hash[i].lock);
                               lock(&rq->__lock);
                               lock(&obj_hash[i].lock);
  lock(&p->pi_lock);

 *** DEADLOCK ***

1 lock held by bch-copygc/loop/7881:
 #0: ffff8000975fb610 (&obj_hash[i].lock){-.-.}-{2:2}, at: __debug_object_init+0x6c/0x40c lib/debugobjects.c:741

stack backtrace:
CPU: 0 UID: 0 PID: 7881 Comm: bch-copygc/loop Not tainted 6.16.0-rc1-syzkaller-g39dfc971e42d #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:466 (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+0x324/0x32c kernel/locking/lockdep.c:2046
 check_noncircular+0x154/0x174 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3168 [inline]
 check_prevs_add kernel/locking/lockdep.c:3287 [inline]
 validate_chain kernel/locking/lockdep.c:3911 [inline]
 __lock_acquire+0x1774/0x30a4 kernel/locking/lockdep.c:5240
 lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5871
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x5c/0x7c kernel/locking/spinlock.c:162
 class_raw_spinlock_irqsave_constructor include/linux/spinlock.h:557 [inline]
 try_to_wake_up+0x68/0xdf0 kernel/sched/core.c:4226
 wake_up_process kernel/sched/core.c:4475 [inline]
 wake_up_q+0x70/0x9c kernel/sched/core.c:1081
 up+0x100/0x170 kernel/locking/semaphore.c:235
 __up_console_sem kernel/printk/printk.c:343 [inline]
 __console_unlock+0x88/0xc4 kernel/printk/printk.c:2885
 __console_flush_and_unlock kernel/printk/printk.c:3287 [inline]
 console_unlock+0xfc/0x288 kernel/printk/printk.c:3325
 vprintk_emit+0x298/0x430 kernel/printk/printk.c:2450
 vprintk_default+0x54/0x80 kernel/printk/printk.c:2465
 vprintk+0x90/0x128 kernel/printk/printk_safe.c:82
 _printk+0xd0/0x118 kernel/printk/printk.c:2475
 __report_bug lib/bug.c:191 [inline]
 report_bug+0x3a8/0x568 lib/bug.c:215
 bug_handler+0x50/0x1fc arch/arm64/kernel/traps.c:1002
 call_break_hook arch/arm64/kernel/debug-monitors.c:315 [inline]
 brk_handler+0x1d8/0x288 arch/arm64/kernel/debug-monitors.c:325
 do_debug_exception+0x1e4/0x38c arch/arm64/mm/fault.c:1002
 el1_dbg+0x64/0x80 arch/arm64/kernel/entry-common.c:513
 el1h_64_sync_handler+0x40/0xcc arch/arm64/kernel/entry-common.c:559
 el1h_64_sync+0x6c/0x70 arch/arm64/kernel/entry.S:595
 debug_object_is_on_stack lib/debugobjects.c:-1 [inline] (P)
 lookup_object_or_alloc lib/debugobjects.c:688 [inline] (P)
 __debug_object_init+0x364/0x40c lib/debugobjects.c:743 (P)
 debug_object_init+0x20/0x2c lib/debugobjects.c:779
 __init_work+0x58/0x68 kernel/workqueue.c:677
 rhashtable_init_noprof+0x734/0xa10 lib/rhashtable.c:1085
 bch2_copygc_thread+0xec/0xd40 fs/bcachefs/movinggc.c:353
 kthread+0x5fc/0x75c kernel/kthread.c:464
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:847
WARNING: CPU: 0 PID: 7881 at lib/debugobjects.c:655 debug_object_is_on_stack lib/debugobjects.c:-1 [inline]
WARNING: CPU: 0 PID: 7881 at lib/debugobjects.c:655 lookup_object_or_alloc lib/debugobjects.c:688 [inline]
WARNING: CPU: 0 PID: 7881 at lib/debugobjects.c:655 __debug_object_init+0x364/0x40c lib/debugobjects.c:743
Modules linked in:
CPU: 0 UID: 0 PID: 7881 Comm: bch-copygc/loop Not tainted 6.16.0-rc1-syzkaller-g39dfc971e42d #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
pstate: 604000c5 (nZCv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : debug_object_is_on_stack lib/debugobjects.c:-1 [inline]
pc : lookup_object_or_alloc lib/debugobjects.c:688 [inline]
pc : __debug_object_init+0x364/0x40c lib/debugobjects.c:743
lr : debug_object_is_on_stack lib/debugobjects.c:-1 [inline]
lr : lookup_object_or_alloc lib/debugobjects.c:688 [inline]
lr : __debug_object_init+0x364/0x40c lib/debugobjects.c:743
sp : ffff80009c337700
x29: ffff80009c337700 x28: 0000000000000000 x27: dfff800000000000
x26: ffff800097693000 x25: ffff0000d2e30020 x24: 0000000000000000
x23: ffff0000f27cbd58 x22: 0000000000000000 x21: ffff8000975fb5f0
x20: ffff80008af70de0 x19: ffff80009c337bb0 x18: 00000000ffffffff
x17: ffff80009331f000 x16: ffff80008aec8e2c x15: 0000000000000001
x14: 1ffff00013866e58 x13: 0000000000000000 x12: 0000000000000000
x11: ffff700013866e59 x10: 0000000000ff0100 x9 : 6623cf50e130e900
x8 : 6623cf50e130e900 x7 : 0000000000000001 x6 : 0000000000000001
x5 : ffff80009c337098 x4 : ffff80008f727060 x3 : ffff8000807c0744
x2 : 0000000000000001 x1 : 0000000100000001 x0 : 0000000000000050
Call trace:
 debug_object_is_on_stack lib/debugobjects.c:-1 [inline] (P)
 lookup_object_or_alloc lib/debugobjects.c:688 [inline] (P)
 __debug_object_init+0x364/0x40c lib/debugobjects.c:743 (P)
 debug_object_init+0x20/0x2c lib/debugobjects.c:779
 __init_work+0x58/0x68 kernel/workqueue.c:677
 rhashtable_init_noprof+0x734/0xa10 lib/rhashtable.c:1085
 bch2_copygc_thread+0xec/0xd40 fs/bcachefs/movinggc.c:353
 kthread+0x5fc/0x75c kernel/kthread.c:464
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:847
irq event stamp: 18
hardirqs last  enabled at (17): [<ffff800083e7f73c>] get_random_u32+0x2d4/0x540 drivers/char/random.c:554
hardirqs last disabled at (18): [<ffff80008aeea2b4>] __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:108 [inline]
hardirqs last disabled at (18): [<ffff80008aeea2b4>] _raw_spin_lock_irqsave+0x2c/0x7c kernel/locking/spinlock.c:162
softirqs last  enabled at (0): [<ffff8000803afb44>] copy_process+0x1134/0x31ec kernel/fork.c:2114
softirqs last disabled at (0): [<0000000000000000>] 0x0
---[ end trace 0000000000000000 ]---