linux-kernel - Re: [PATCH v4] CPU hotplug: active_writer not woken up in some cases

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Message-ID: <20141210202340.1cc25999@thinkpad-w530>
Date:	Wed, 10 Dec 2014 20:23:40 +0100
From:	David Hildenbrand <dahi@...ux.vnet.ibm.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, heiko.carstens@...ibm.com,
	borntraeger@...ibm.com, rafael.j.wysocki@...el.com,
	peterz@...radead.org, oleg@...hat.com, bp@...e.de, jkosina@...e.cz
Subject: Re: [PATCH v4] CPU hotplug: active_writer not woken up in some
 cases - deadlock

only thing that is bugging me is this part. Without the lock we can't
> > guarantee that another get_online_cpus() just arrived and bumped the refcount
> > to 0.
> > 
> > Of course this only applies to misuse of put/get_online_cpus.
> > 
> > We could hack some loop that tries to cmp_xchng with the old value until it
> > fits to work around this, but wouldn't make the code any better readable.
> 
> Well, we didn't have this diagnostic in the original, so one approach
> would be to simply leave it out.  Another approach would be to just
> have the WARN_ON() without the attempt to fix it up.
> 
> 							Thanx, Paul

Well, I think the WARN_ON would be sufficient for debugging purposes.

Thanks!

David

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