linux-kernel - Re: [patch V2 24/24] cpu/hotplug: Convert hotplug locking to percpu rwsem

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Message-ID: <alpine.DEB.2.20.1705101047200.1979@nanos>
Date:   Wed, 10 May 2017 10:49:09 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Michael Ellerman <mpe@...erman.id.au>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Siewior <bigeasy@...utronix.de>
Subject: Re: [patch V2 24/24] cpu/hotplug: Convert hotplug locking to percpu
 rwsem

On Wed, 10 May 2017, Michael Ellerman wrote:

> Thomas Gleixner <tglx@...utronix.de> writes:
> 
> > @@ -130,6 +130,7 @@ void __static_key_slow_inc(struct static
> >  	 * the all CPUs, for that to be serialized against CPU hot-plug
> >  	 * we need to avoid CPUs coming online.
> >  	 */
> > +	lockdep_assert_hotplug_held();
> >  	jump_label_lock();
> >  	if (atomic_read(&key->enabled) == 0) {
> >  		atomic_set(&key->enabled, -1);
> 
> I seem to be hitting this assert from the ftrace event selftests,
> enabled at boot with CONFIG_FTRACE_STARTUP_TEST=y, using next-20170509
> (on powerpc).
> 
> The stupidly obvious (or perhaps obviously stupid) patch below fixes it:

Kinda. There is more horror in that area lurking and I'm still trying to
figure out all the convoluted call pathes.

Thanks,

	tglx

> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index daefdee9411a..5531f7ce8fa6 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -3241,9 +3241,19 @@ static __init void event_trace_self_tests(void)
>  			continue;
>  		}
>  
> +		get_online_cpus();
> +		mutex_lock(&event_mutex);
>  		ftrace_event_enable_disable(file, 1);
> +		mutex_unlock(&event_mutex);
> +		put_online_cpus();
> +
>  		event_test_stuff();
> +
> +		get_online_cpus();
> +		mutex_lock(&event_mutex);
>  		ftrace_event_enable_disable(file, 0);
> +		mutex_unlock(&event_mutex);
> +		put_online_cpus();
>  
>  		pr_cont("OK\n");
>  	}
> 
> cheers
>