Re: [LOCKDEP SPLAT 4.14-rc1] Conflict between smpboot thread create completions and get_online_cpus

[Peter Zijlstra]

On Mon, Sep 18, 2017 at 03:24:59PM -0400, Steven Rostedt wrote:
> And adding some debugging where the lockdep splat happened:
> 
>  watchdog-27      3.... 764857us : cpus_read_lock+0x5/0xc0: lock cpu
>  watchdog-27      3.... 764858us : <stack trace>
>   => x86_release_hardware+0x8f/0xa0
>   => hw_perf_event_destroy+0xe/0x20
>   => _free_event+0xca/0x3d0
>   => put_event+0x14/0x20
>   => perf_event_release_kernel+0x236/0x330
>   => watchdog_nmi_disable+0x49/0x70
>   => watchdog_disable+0x4d/0x60
>   => smpboot_thread_fn+0x138/0x280
>   => kthread+0x152/0x190
>   => ret_from_fork+0x2a/0x40
>  watchdog-27      3.... 764917us : cpus_read_unlock+0x5/0xa0: unlock cpu
>  watchdog-27      3d..1 764918us : lock_commit_crosslock+0xc1/0x5b0: xhlock=132

Yeah, known issue. Thomas has already been prodding at the watchdog
stuff.