* [syzbot] [kernel?] possible deadlock in __balance_push_cpu_stop
@ 2026-08-29 4:50 syzbot
2026-08-30 14:58 ` [syzbot] [fs?] " syzbot
0 siblings, 1 reply; 2+ messages in thread
From: syzbot @ 2026-08-29 4:50 UTC (permalink / raw)
To: bp, dave.hansen, hpa, linux-kernel, mingo, syzkaller-bugs, tglx, x86
Hello,
syzbot found the following issue on:
HEAD commit: 18fbf5151d2c Merge tag 'mm-stable-2026-08-26-15-22' of git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14737415580000
kernel config: https://syzkaller.appspot.com/x/.config?x=315b9470ea1919b5
dashboard link: https://syzkaller.appspot.com/bug?extid=acf142088e0182172e58
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/048de1af0091/disk-18fbf515.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/40ec4a36602a/vmlinux-18fbf515.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d49e157a8ad0/bzImage-18fbf515.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+acf142088e0182172e58@syzkaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
migration/1/27 is trying to acquire lock:
ffff8880b8740998 (_T->lock){....}-{2:2}, at: rt_mutex_slowtrylock kernel/locking/rtmutex.c:1404 [inline]
ffff8880b8740998 (_T->lock){....}-{2:2}, at: __rt_spin_trylock kernel/locking/spinlock_rt.c:123 [inline]
ffff8880b8740998 (_T->lock){....}-{2:2}, at: rt_spin_trylock+0x56/0x2b0 kernel/locking/spinlock_rt.c:135
but task is already holding lock:
ffff88802718e8c0 (&p->pi_lock){-...}-{2:2}, at: class_raw_spinlock_irq_constructor include/linux/spinlock.h:575 [inline]
ffff88802718e8c0 (&p->pi_lock){-...}-{2:2}, at: __balance_push_cpu_stop+0x78/0x410 kernel/sched/core.c:8446
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&p->pi_lock){-...}-{2:2}:
__raw_spin_lock include/linux/spinlock_api_smp.h:190 [inline]
_raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:173
rtlock_slowlock_locked+0x1ec/0x3c20 kernel/locking/rtmutex.c:1874
rtlock_slowlock kernel/locking/rtmutex.c:1922 [inline]
rtlock_lock kernel/locking/spinlock_rt.c:43 [inline]
__rt_spin_lock kernel/locking/spinlock_rt.c:49 [inline]
rt_spin_lock+0x165/0x400 kernel/locking/spinlock_rt.c:57
spin_lock include/linux/spinlock_rt.h:45 [inline]
finish_wait+0xbe/0x1e0 kernel/sched/wait.c:395
synchronize_rcu_expedited+0x63e/0x770 kernel/rcu/tree_exp.h:981
srcu_readers_active_idx_check kernel/rcu/srcutree.c:540 [inline]
try_check_zero+0x2c1/0x4c0 kernel/rcu/srcutree.c:1135
srcu_advance_state kernel/rcu/srcutree.c:1845 [inline]
process_srcu+0x328/0x16f0 kernel/rcu/srcutree.c:1954
process_one_work kernel/workqueue.c:3387 [inline]
process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3470
worker_thread+0xa47/0xfb0 kernel/workqueue.c:3551
kthread+0x38b/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #0 (_T->lock){....}-{2:2}:
check_prev_add kernel/locking/lockdep.c:3181 [inline]
check_prevs_add kernel/locking/lockdep.c:3300 [inline]
validate_chain kernel/locking/lockdep.c:3924 [inline]
__lock_acquire+0x15ff/0x2e40 kernel/locking/lockdep.c:5254
lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5908
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:155 [inline]
_raw_spin_lock_irqsave+0x40/0x60 kernel/locking/spinlock.c:181
rt_mutex_slowtrylock kernel/locking/rtmutex.c:1404 [inline]
__rt_spin_trylock kernel/locking/spinlock_rt.c:123 [inline]
rt_spin_trylock+0x56/0x2b0 kernel/locking/spinlock_rt.c:135
__kfree_rcu_sheaf+0xd3/0x620 mm/slub.c:6113
kfree_rcu_sheaf mm/slab_common.c:1688 [inline]
kvfree_call_rcu+0xa4/0x430 mm/slab_common.c:2037
set_cpus_allowed_force+0x1bd/0x2a0 kernel/sched/core.c:2833
cpuset_cpus_allowed_fallback+0x24a/0x370 kernel/cgroup/cpuset.c:4258
select_fallback_rq+0x11e/0x200 kernel/sched/core.c:3589
__balance_push_cpu_stop+0xa1/0x410 kernel/sched/core.c:8453
cpu_stopper_thread+0x25e/0x3f0 kernel/stop_machine.c:510
smpboot_thread_fn+0x565/0xa70 kernel/smpboot.c:160
kthread+0x38b/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&p->pi_lock);
lock(_T->lock);
lock(&p->pi_lock);
lock(_T->lock);
*** DEADLOCK ***
locks held by migration/1/27: 2, last CPU#1:
#0: ffff88802718e8c0 (&p->pi_lock){-...}-{2:2}, at: class_raw_spinlock_irq_constructor include/linux/spinlock.h:575 [inline]
#0: ffff88802718e8c0 (&p->pi_lock){-...}-{2:2}, at: __balance_push_cpu_stop+0x78/0x410 kernel/sched/core.c:8446
#1: ffffffff8e1c3ac0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline]
#1: ffffffff8e1c3ac0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
#1: ffffffff8e1c3ac0 (rcu_read_lock){....}-{1:3}, at: cpuset_cpus_allowed_fallback+0x22/0x370 kernel/cgroup/cpuset.c:4255
stack backtrace:
CPU: 1 UID: 0 PID: 27 Comm: migration/1 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Stopper: __balance_push_cpu_stop+0x0/0x410 kernel/sched/sched.h:3965 <- balance_push+0x28d/0x4f0
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2059
check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2191
check_prev_add kernel/locking/lockdep.c:3181 [inline]
check_prevs_add kernel/locking/lockdep.c:3300 [inline]
validate_chain kernel/locking/lockdep.c:3924 [inline]
__lock_acquire+0x15ff/0x2e40 kernel/locking/lockdep.c:5254
lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5908
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:155 [inline]
_raw_spin_lock_irqsave+0x40/0x60 kernel/locking/spinlock.c:181
rt_mutex_slowtrylock kernel/locking/rtmutex.c:1404 [inline]
__rt_spin_trylock kernel/locking/spinlock_rt.c:123 [inline]
rt_spin_trylock+0x56/0x2b0 kernel/locking/spinlock_rt.c:135
__kfree_rcu_sheaf+0xd3/0x620 mm/slub.c:6113
kfree_rcu_sheaf mm/slab_common.c:1688 [inline]
kvfree_call_rcu+0xa4/0x430 mm/slab_common.c:2037
set_cpus_allowed_force+0x1bd/0x2a0 kernel/sched/core.c:2833
cpuset_cpus_allowed_fallback+0x24a/0x370 kernel/cgroup/cpuset.c:4258
select_fallback_rq+0x11e/0x200 kernel/sched/core.c:3589
__balance_push_cpu_stop+0xa1/0x410 kernel/sched/core.c:8453
cpu_stopper_thread+0x25e/0x3f0 kernel/stop_machine.c:510
smpboot_thread_fn+0x565/0xa70 kernel/smpboot.c:160
kthread+0x38b/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
process 5837 (syz.3.12) no longer affine to cpu1
---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.
syzbot will keep track of this issue. See:
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If the report is already addressed, let syzbot know by replying with:
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If you want to overwrite report's subsystems, reply with:
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If the report is a duplicate of another one, reply with:
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If you want to undo deduplication, reply with:
#syz undup
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [syzbot] [fs?] possible deadlock in __balance_push_cpu_stop
2026-08-29 4:50 [syzbot] [kernel?] possible deadlock in __balance_push_cpu_stop syzbot
@ 2026-08-30 14:58 ` syzbot
0 siblings, 0 replies; 2+ messages in thread
From: syzbot @ 2026-08-30 14:58 UTC (permalink / raw)
To: bp, dave.hansen, hpa, linux-fsdevel, linux-kernel, mingo,
syzkaller-bugs, tglx, x86
syzbot has found a reproducer for the following issue on:
HEAD commit: 08dbfad3f504 Merge tag 'for-linus' of git://git.kernel.org..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=154fb379580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b454dc6b1b7acd30
dashboard link: https://syzkaller.appspot.com/bug?extid=acf142088e0182172e58
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17c19379580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=134fb379580000
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/8aa9167f616f/disk-08dbfad3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9ec932d59de3/vmlinux-08dbfad3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/86e2243e886e/bzImage-08dbfad3.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+acf142088e0182172e58@syzkaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
migration/1/27 is trying to acquire lock:
ffff8880b8740998 (_T->lock){....}-{2:2}, at: rt_mutex_slowtrylock kernel/locking/rtmutex.c:1404 [inline]
ffff8880b8740998 (_T->lock){....}-{2:2}, at: __rt_spin_trylock kernel/locking/spinlock_rt.c:123 [inline]
ffff8880b8740998 (_T->lock){....}-{2:2}, at: rt_spin_trylock+0x56/0x2b0 kernel/locking/spinlock_rt.c:135
but task is already holding lock:
ffff88803cefe8c0 (&p->pi_lock){-...}-{2:2}, at: class_raw_spinlock_irq_constructor include/linux/spinlock.h:575 [inline]
ffff88803cefe8c0 (&p->pi_lock){-...}-{2:2}, at: __balance_push_cpu_stop+0x78/0x410 kernel/sched/core.c:8446
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&p->pi_lock){-...}-{2:2}:
__raw_spin_lock include/linux/spinlock_api_smp.h:190 [inline]
_raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:173
rtlock_slowlock_locked+0x1ec/0x3c20 kernel/locking/rtmutex.c:1874
rtlock_slowlock kernel/locking/rtmutex.c:1922 [inline]
rtlock_lock kernel/locking/spinlock_rt.c:43 [inline]
__rt_spin_lock kernel/locking/spinlock_rt.c:49 [inline]
rt_spin_lock+0x165/0x400 kernel/locking/spinlock_rt.c:57
spin_lock include/linux/spinlock_rt.h:45 [inline]
finish_wait+0xbe/0x1e0 kernel/sched/wait.c:395
synchronize_rcu_expedited+0x63e/0x770 kernel/rcu/tree_exp.h:981
srcu_readers_active_idx_check kernel/rcu/srcutree.c:538 [inline]
try_check_zero+0x2c8/0x4c0 kernel/rcu/srcutree.c:1135
srcu_advance_state kernel/rcu/srcutree.c:1827 [inline]
process_srcu+0x148/0x16f0 kernel/rcu/srcutree.c:1954
process_one_work kernel/workqueue.c:3387 [inline]
process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3470
worker_thread+0xa47/0xfb0 kernel/workqueue.c:3551
kthread+0x38b/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #0 (_T->lock){....}-{2:2}:
check_prev_add kernel/locking/lockdep.c:3181 [inline]
check_prevs_add kernel/locking/lockdep.c:3300 [inline]
validate_chain kernel/locking/lockdep.c:3924 [inline]
__lock_acquire+0x15ff/0x2e40 kernel/locking/lockdep.c:5254
lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5908
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:155 [inline]
_raw_spin_lock_irqsave+0x40/0x60 kernel/locking/spinlock.c:181
rt_mutex_slowtrylock kernel/locking/rtmutex.c:1404 [inline]
__rt_spin_trylock kernel/locking/spinlock_rt.c:123 [inline]
rt_spin_trylock+0x56/0x2b0 kernel/locking/spinlock_rt.c:135
__kfree_rcu_sheaf+0xd3/0x620 mm/slub.c:6113
kfree_rcu_sheaf mm/slab_common.c:1688 [inline]
kvfree_call_rcu+0xa4/0x430 mm/slab_common.c:2037
set_cpus_allowed_force+0x1bd/0x2a0 kernel/sched/core.c:2833
cpuset_cpus_allowed_fallback+0x24a/0x370 kernel/cgroup/cpuset.c:4258
select_fallback_rq+0x11e/0x200 kernel/sched/core.c:3589
__balance_push_cpu_stop+0xa1/0x410 kernel/sched/core.c:8453
cpu_stopper_thread+0x25e/0x3f0 kernel/stop_machine.c:510
smpboot_thread_fn+0x565/0xa70 kernel/smpboot.c:160
kthread+0x38b/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&p->pi_lock);
lock(_T->lock);
lock(&p->pi_lock);
lock(_T->lock);
*** DEADLOCK ***
locks held by migration/1/27: 2, last CPU#1:
#0: ffff88803cefe8c0 (&p->pi_lock){-...}-{2:2}, at: class_raw_spinlock_irq_constructor include/linux/spinlock.h:575 [inline]
#0: ffff88803cefe8c0 (&p->pi_lock){-...}-{2:2}, at: __balance_push_cpu_stop+0x78/0x410 kernel/sched/core.c:8446
#1: ffffffff8e1c3ac0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline]
#1: ffffffff8e1c3ac0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
#1: ffffffff8e1c3ac0 (rcu_read_lock){....}-{1:3}, at: cpuset_cpus_allowed_fallback+0x22/0x370 kernel/cgroup/cpuset.c:4255
stack backtrace:
CPU: 1 UID: 0 PID: 27 Comm: migration/1 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Stopper: __balance_push_cpu_stop+0x0/0x410 kernel/sched/sched.h:3965 <- balance_push+0x28d/0x4f0
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2059
check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2191
check_prev_add kernel/locking/lockdep.c:3181 [inline]
check_prevs_add kernel/locking/lockdep.c:3300 [inline]
validate_chain kernel/locking/lockdep.c:3924 [inline]
__lock_acquire+0x15ff/0x2e40 kernel/locking/lockdep.c:5254
lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5908
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:155 [inline]
_raw_spin_lock_irqsave+0x40/0x60 kernel/locking/spinlock.c:181
rt_mutex_slowtrylock kernel/locking/rtmutex.c:1404 [inline]
__rt_spin_trylock kernel/locking/spinlock_rt.c:123 [inline]
rt_spin_trylock+0x56/0x2b0 kernel/locking/spinlock_rt.c:135
__kfree_rcu_sheaf+0xd3/0x620 mm/slub.c:6113
kfree_rcu_sheaf mm/slab_common.c:1688 [inline]
kvfree_call_rcu+0xa4/0x430 mm/slab_common.c:2037
set_cpus_allowed_force+0x1bd/0x2a0 kernel/sched/core.c:2833
cpuset_cpus_allowed_fallback+0x24a/0x370 kernel/cgroup/cpuset.c:4258
select_fallback_rq+0x11e/0x200 kernel/sched/core.c:3589
__balance_push_cpu_stop+0xa1/0x410 kernel/sched/core.c:8453
cpu_stopper_thread+0x25e/0x3f0 kernel/stop_machine.c:510
smpboot_thread_fn+0x565/0xa70 kernel/smpboot.c:160
kthread+0x38b/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
process 5610 (syz-executor350) no longer affine to cpu1
---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.
^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2026-08-30 14:58 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
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2026-08-30 14:58 ` [syzbot] [fs?] " syzbot
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