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Date: Wed, 1 Nov 2017 09:14:50 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Guenter Roeck <linux@roeck-us.net>, linux-kernel@vger.kernel.org,
        Don Zickus <dzickus@redhat.com>, Ingo Molnar <mingo@kernel.org>
Subject: Re: Crashes in perf_event_ctx_lock_nested
Message-ID: <20171101081450.waqzz2ftebaw3tal@hirez.programming.kicks-ass.net>
References: <20171030224512.GA13592@roeck-us.net>
 <20171031134850.ynix2zqypmca2mtt@hirez.programming.kicks-ass.net>
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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?