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

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Date:   Thu, 11 May 2017 15:49:21 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Thomas Gleixner <tglx@...utronix.de>
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

Thomas Gleixner <tglx@...utronix.de> writes:

> 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.

OK thanks.

cheers