Date: Thu, 6 Feb 2014 19:41:03 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Cc: paulus@samba.org, rusty@rustcorp.com.au, peterz@infradead.org,
        tglx@linutronix.de, akpm@linux-foundation.org, mingo@kernel.org,
        paulmck@linux.vnet.ibm.com, tj@kernel.org, walken@google.com,
        ego@linux.vnet.ibm.com, linux@arm.linux.org.uk,
        linux-kernel@vger.kernel.org, Toshi Kani <toshi.kani@hp.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Subject: Re: [PATCH 01/51] CPU hotplug: Provide lockless versions of
	callback registration functions
Message-ID: <20140206184103.GA31410@redhat.com>
References: <20140205220251.19080.92336.stgit@srivatsabhat.in.ibm.com> <20140205220447.19080.9460.stgit@srivatsabhat.in.ibm.com>
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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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