linux-kernel - Re: Crashes in perf_event_ctx_lock

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Message-ID: <alpine.DEB.2.20.1711010926170.1942@nanos>
Date:   Wed, 1 Nov 2017 09:26:35 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
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 Wed, 1 Nov 2017, Peter Zijlstra wrote:

> 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?

probe() releases the event.