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

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Message-ID: <20180124153257.kzekv6cjxgk7djkh@gmail.com>
Date:   Wed, 24 Jan 2018 16:32:57 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     hpa@...or.com, tglx@...utronix.de, linux-kernel@...r.kernel.org,
        rostedt@...dmis.org, torvalds@...ux-foundation.org,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/urgent] perf/core: Fix lock inversion between
 perf,trace,cpuhp


* Peter Zijlstra <peterz@...radead.org> wrote:

> 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@...radead.org>
> > AuthorDate: Tue, 9 Jan 2018 13:10:30 +0100
> > Committer:  Ingo Molnar <mingo@...nel.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.

Oh, the '#' was probably interpreted as a comment when I applied it ...

Thanks,

	Ingo