Re: BUG: spinlock bad magic in lock_timer_base

[Thomas Gleixner <tglx@linutronix.de>]

On Thu, Jul 03 2025 at 16:54, 白烁冉 wrote:

> Dear Maintainers,

The timer maintainers are hardly the right group to ask. The timer code
is just the messenger :)

I've Cc'ed the KVM folks, as you correctly identified KVM already as the
probable source of the problem.

> When using our customized Syzkaller to fuzz the latest Linux kernel, the following crash (110th)was triggered.

6.14 is not really the latest kernel.

> HEAD commit: 6537cfb395f352782918d8ee7b7f10ba2cc3cbf2
> git tree: upstream
> Output:https://github.com/pghk13/Kernel-Bug/blob/main/0702_6.14/BUG%3A%20spinlock%20bad%20magic%20in%20lock_timer_base/report110.txt 
> Kernel config:https://github.com/pghk13/Kernel-Bug/blob/main/0702_6.14/config.txt
> C reproducer:https://github.com/pghk13/Kernel-Bug/blob/main/0702_6.14/BUG%3A%20spinlock%20bad%20magic%20in%20lock_timer_base/110repro.c Syzlang 
> reproducer:https://github.com/pghk13/Kernel-Bug/blob/main/0702_6.14/BUG%3A%20spinlock%20bad%20magic%20in%20lock_timer_base/110repro.txt Our reproducer uses mounts a constructed filesystem image.
>  
> The error occurs in the lock_timer_base (timer.c lines 1770-1790 or
> so). It happens cleanup_srcu_struct during the KVM VM shutdown
> process, and it is likely that the memory pointed to by the timer
> object has been freed. The timer_base pointer returned by the
> get_timer_base (tf) points to an invalid memory area
> (__init_begin+0x2a500)

If you enable DEBUG_OBJECTS_TIMERS and DEBUG_OBJECTS_FREE the kernel
should survive and provide some useful output.

> We have reproduced this issue several times on 6.14 again.

Does the probkem still exist on the latest upstream kernel release
candidate, i.e. v6.16-rc4?

Leaving the report context intact for kvm folks.

Thanks,

        tglx
    

> If you fix this issue, please add the following tag to the commit:
> Reported-by: Kun Hu <huk23@m.fudan.edu.cn>, Jiaji Qin <jjtan24@m.fudan.edu.cn>, Shuoran Bai <baishuoran@hrbeu.edu.cn>
>
>
>
>
> BUG: spinlock bad magic on CPU#2, syz.6.399/18129
>  lock: __init_begin+0x2a500/0x41000, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
> CPU: 2 UID: 0 PID: 18129 Comm: syz.6.399 Not tainted 6.14.0 #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x116/0x1b0
>  do_raw_spin_lock+0x22c/0x2e0
>  _raw_spin_lock_irqsave+0x45/0x60
>  lock_timer_base+0x125/0x1c0
>  __try_to_del_timer_sync+0x7f/0x160
>  __timer_delete_sync+0x120/0x1c0
>  cleanup_srcu_struct+0x122/0x5a0
>  kvm_put_kvm+0x7c9/0xa10
>  kvm_vcpu_release+0x4b/0x70
>  __fput+0x417/0xb60
>  __fput_sync+0xa6/0xc0
>  __x64_sys_close+0x8b/0x120
>  do_syscall_64+0xcf/0x250
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fafdad1ebdb
> Code: 03 00 00 00 0f 05 48 3d 00 f0 ff ff 77 41 c3 48 83 ec 18 89 7c 24 0c e8 63 fc ff ff 8b 7c 24 0c 41 89 c0 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 2f 44 89 c7 89 44 24 0c e8 a1 fc ff ff 8b 44
> RSP: 002b:00007ffde8c95b20 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
> RAX: ffffffffffffffda RBX: 0000000000000006 RCX: 00007fafdad1ebdb
> RDX: ffffffffffffffff RSI: 0000000000000000 RDI: 0000000000000005
> RBP: 00007ffde8c95bf8 R08: 0000000000000000 R09: 00007fafda8015a6
> R10: 0000000000000001 R11: 0000000000000293 R12: 00007fafdafa5fa0
> R13: 000000000002f3ea R14: ffffffffffffffff R15: 00007fafdafa5fa0
>  </TASK>