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

From: Ingo Molnar
Date: Wed Jan 24 2018 - 10:33:07 EST



* Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > AuthorDate: Tue, 9 Jan 2018 13:10:30 +0100
> > Committer: Ingo Molnar <mingo@xxxxxxxxxx>
> > 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