linux-kernel - Re: [RFC PATCH v3 1/9] CPU hotplug: Provide APIs to prevent CPU offline from atomic context

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Message-ID: <20121207181608.GB2821@htj.dyndns.org>
Date:	Fri, 7 Dec 2012 10:16:08 -0800
From:	Tejun Heo <tj@...nel.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	tglx@...utronix.de, peterz@...radead.org,
	paulmck@...ux.vnet.ibm.com, rusty@...tcorp.com.au,
	mingo@...nel.org, akpm@...ux-foundation.org, namhyung@...nel.org,
	vincent.guittot@...aro.org, oleg@...hat.com, sbw@....edu,
	amit.kucheria@...aro.org, rostedt@...dmis.org, rjw@...k.pl,
	wangyun@...ux.vnet.ibm.com, xiaoguangrong@...ux.vnet.ibm.com,
	nikunj@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v3 1/9] CPU hotplug: Provide APIs to prevent CPU
 offline from atomic context

Hello, again.

On Fri, Dec 07, 2012 at 09:57:24AM -0800, Tejun Heo wrote:
> possible.  Also, I think the right approach would be auditing each
> get_online_cpus_atomic() callsites and figure out proper locking order
> rather than implementing a construct this unusual especially as
> hunting down the incorrect cases shouldn't be difficult given proper
> lockdep annotation.

On the second look, it looks like you're implementing proper
percpu_rwlock semantics as readers aren't supposed to induce circular
dependency directly.  Can you please work with Oleg to implement
proper percpu-rwlock and use that for CPU hotplug rather than
implementing it inside CPU hotplug?

Thanks.

-- 
tejun
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