linux-kernel - Re: [PATCH 01/51] CPU hotplug: Provide lockless versions of callback registration functions

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Message-ID: <20140206184103.GA31410@redhat.com>
Date:	Thu, 6 Feb 2014 19:41:03 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	paulus@...ba.org, rusty@...tcorp.com.au, peterz@...radead.org,
	tglx@...utronix.de, akpm@...ux-foundation.org, mingo@...nel.org,
	paulmck@...ux.vnet.ibm.com, tj@...nel.org, walken@...gle.com,
	ego@...ux.vnet.ibm.com, linux@....linux.org.uk,
	linux-kernel@...r.kernel.org, Toshi Kani <toshi.kani@...com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH 01/51] CPU hotplug: Provide lockless versions of
	callback registration functions

On 02/06, Srivatsa S. Bhat wrote:
>
> The following method of CPU hotplug callback registration is not safe
> due to the possibility of an ABBA deadlock involving the cpu_add_remove_lock
> and the cpu_hotplug.lock.

Off-topic, but perhaps it also makes sense to add the lockdep annotations
later, to catch other similar problems. Currently get_online_cpus() acquires
nothing from lockdep pov.


As for the this patch/series, personally I agree.

Oleg.

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