Re: WARNING: possible circular locking dependency detected

From	Thomas Gleixner <tglx@linutronix.de>
Newsgroups	linux.kernel
Subject	Re: WARNING: possible circular locking dependency detected
Date	2017-08-31 23:30 +0200
Message-ID	<ukFcf-2CI-15@gated-at.bofh.it> (permalink)
References	(6 earlier) <ukrLY-2y1-25@gated-at.bofh.it> <uksf1-2Jn-27@gated-at.bofh.it> <uksym-2Q9-17@gated-at.bofh.it> <uksI3-38N-41@gated-at.bofh.it> <uksRI-3bX-29@gated-at.bofh.it>
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On Thu, 31 Aug 2017, Thomas Gleixner wrote:
> On Thu, 31 Aug 2017, Peter Zijlstra wrote:
> 
> > On Thu, Aug 31, 2017 at 09:55:57AM +0200, Thomas Gleixner wrote:
> > > > Arghh!!!
> > > > 
> > > > And allowing us to create events for offline CPUs (possible I think, but
> > > > maybe slightly tricky) won't solve that, because we're already holding
> > > > the hotplug_lock during PREPARE.
> > > 
> > > There are two ways to cure that:
> > > 
> > > 1) Have a pre cpus_write_lock() stage which is serialized via
> > >    cpus_add_remove_lock, which is the outer lock for hotplug.
> > > 
> > >    There we can sanely create stuff and fail with all consequences.
> > 
> > True, if you're willing to add more state to that hotplug thing I'll try
> > and make that perf patch that allows attaching to offline CPUs.
> 
> Now that I think more about it. That's going to be an interesting exercise
> vs. the hotplug state registration which relies on cpus_read_lock()
> serialization.....

We could have that for built-in stuff which is guaranteed to be never
unregistered. Pretty restricted, but for cases like that it could
work. Famous last work ...

Thanks,

	tglx

Thread

Re: WARNING: possible circular locking dependency detected Peter Zijlstra <peterz@infradead.org> - 2017-08-28 17:00 +0200
  Re: WARNING: possible circular locking dependency detected Peter Zijlstra <peterz@infradead.org> - 2017-08-28 17:10 +0200
    Re: WARNING: possible circular locking dependency detected Peter Zijlstra <peterz@infradead.org> - 2017-08-28 18:40 +0200
  Re: WARNING: possible circular locking dependency detected Thomas Gleixner <tglx@linutronix.de> - 2017-08-29 19:50 +0200
    Re: WARNING: possible circular locking dependency detected Peter Zijlstra <peterz@infradead.org> - 2017-08-29 21:50 +0200
      Re: WARNING: possible circular locking dependency detected Thomas Gleixner <tglx@linutronix.de> - 2017-08-29 22:20 +0200
        Re: WARNING: possible circular locking dependency detected Peter Zijlstra <peterz@infradead.org> - 2017-08-30 07:50 +0200
          Re: WARNING: possible circular locking dependency detected Thomas Gleixner <tglx@linutronix.de> - 2017-08-31 09:10 +0200
            Re: WARNING: possible circular locking dependency detected Peter Zijlstra <peterz@infradead.org> - 2017-08-31 09:40 +0200
              Re: WARNING: possible circular locking dependency detected Thomas Gleixner <tglx@linutronix.de> - 2017-08-31 10:00 +0200
                Re: WARNING: possible circular locking dependency detected Peter Zijlstra <peterz@infradead.org> - 2017-08-31 10:10 +0200
                Re: WARNING: possible circular locking dependency detected Thomas Gleixner <tglx@linutronix.de> - 2017-08-31 10:20 +0200
                Re: WARNING: possible circular locking dependency detected Thomas Gleixner <tglx@linutronix.de> - 2017-08-31 23:30 +0200
                Re: WARNING: possible circular locking dependency detected Peter Zijlstra <peterz@infradead.org> - 2017-09-01 22:40 +0200

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