linux-kernel - Re: Crashes in perf_event_ctx_lock

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Message-ID: <20171101081450.waqzz2ftebaw3tal@hirez.programming.kicks-ass.net>
Date:   Wed, 1 Nov 2017 09:14:50 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Guenter Roeck <linux@...ck-us.net>, linux-kernel@...r.kernel.org,
        Don Zickus <dzickus@...hat.com>, Ingo Molnar <mingo@...nel.org>
Subject: Re: Crashes in perf_event_ctx_lock_nested

On Tue, Oct 31, 2017 at 10:32:00PM +0100, Thomas Gleixner wrote:
> That means we can have the following situation:
> 
>     lock(watchdog_mutex);
>     lockup_detector_reconfigure();
>         cpus_read_lock();
> 	stop();
> 	   park()
> 	update();
> 	start();
> 	   unpark()
> 	cpus_read_unlock();		thread runs()
> 	cleanup();						
>     unlock(watchdog_mutex);
> 

Isn't there also a where hardlockup_detector_perf_init() creates an
event to 'probe' stuff, and then hardlockup_detector_perf_enable()
_again_ creates the event?