Re: [tip:perf/urgent] perf/core: Fix lock inversion between perf,trace,cpuhp

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Jan 24, 2018 at 02:39:16AM -0800, tip-bot for Peter Zijlstra wrote:
> Commit-ID:  25695067c32e34047b5490436a90af507fda1c2e
> Gitweb:     https://git.kernel.org/tip/25695067c32e34047b5490436a90af507fda1c2e
> Author:     Peter Zijlstra <peterz@infradead.org>
> AuthorDate: Tue, 9 Jan 2018 13:10:30 +0100
> Committer:  Ingo Molnar <mingo@kernel.org>
> CommitDate: Wed, 24 Jan 2018 10:07:23 +0100
> 
> perf/core: Fix lock inversion between perf,trace,cpuhp
> 
> Lockdep gifted us with noticing the following race:
> 
>         perf_trace_init()
>           perf_trace_event_init()
>             perf_trace_event_reg()
>               tp_event->class->reg() := tracepoint_probe_register
>                   trace_point_add_func()
> 
>           perf_event_init_cpu()
> 
>         perf_event_task_disable()
>           mutex_lock(&current->perf_event_mutex)
> 
>         do_exit()
>           task_work_run()
>             __fput()
>               perf_release()
>                 perf_event_release_kernel()
>                   free_event()
>                     _free_event()
>                       event->destroy() := perf_trace_destroy
> 

You seem to have lost part of the Changelog, mine looks like:

        perf_trace_init()
#0        mutex_lock(&event_mutex)
          perf_trace_event_init()
            perf_trace_event_reg()
              tp_event->class->reg() := tracepoint_probe_register
#1              mutex_lock(&tracepoints_mutex)
                  trace_point_add_func()
#2                  static_key_enable()


#2      do_cpu_up()
          perf_event_init_cpu()
#3          mutex_lock(&pmus_lock)
#4          mutex_lock(&ctx->mutex)


        perf_event_task_disable()
          mutex_lock(&current->perf_event_mutex)
#4        ctx = perf_event_ctx_lock()
#5        perf_event_for_each_child()


        do_exit()
          task_work_run()
            __fput()
              perf_release()
                perf_event_release_kernel()
#4                mutex_lock(&ctx->mutex)
#5                mutex_lock(&event->child_mutex)
                  free_event()
                    _free_event()
                      event->destroy() := perf_trace_destroy
#0                      mutex_lock(&event_mutex);



Which shows an actual deadlock.