linux-kernel - Re: [PATCH 7/8] percpu: add __percpu sparse annotations to hw

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Message-ID: <4B5E401D.2020809@zytor.com>
Date:	Mon, 25 Jan 2010 17:06:37 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
	axboe@...nel.dk, rusty@...tcorp.com.au, akpm@...ux-foundation.org,
	ebiederm@...ssion.com, tytso@....edu, Trond.Myklebust@...app.com,
	aelder@....com, hch@...radead.org, viro@...iv.linux.org.uk,
	davem@...emloft.net, netdev@...r.kernel.org, x86@...nel.org,
	mingo@...hat.com, dan.j.williams@...el.com,
	borislav.petkov@....com, ying.huang@...el.com, lenb@...nel.org,
	neilb@...e.de, cl@...ux-foundation.org
Subject: Re: [PATCH 7/8] percpu: add __percpu sparse annotations to	hw_breakpoint

On 01/25/2010 04:19 PM, Frederic Weisbecker wrote:
> On Tue, Jan 26, 2010 at 12:22:14AM +0900, Tejun Heo wrote:
>> Add __percpu sparse annotations to hw_breakpoint.
>>
>> These annotations are to make sparse consider percpu variables to be
>> in a different address space and warn if accessed without going
>> through percpu accessors.  This patch doesn't affect normal builds.
>>
>> per_cpu(nr_task_bp_pinned, cpu) is replaced with
>> &per_cpu(nr_task_bp_pinned[0], cpu).  This is the same to the compiler
>> but allows per_cpu() macro to correctly drop __percpu designation for
>> the returned pointer.
> 
> Ouch... It's unpleasant to see such workaround that messes up the
> code just to make sparse happy.
> 
> I guess __percpu is an address_space attribute? Is there no
> way to force the address space change directly from the
> per_cpu() macro?
> 

Hmm... thinking more about it, we should be able to just move the & and
[0] into the per_cpu() macro, addressing the situation, or does that
cause problems elsewhere?

	-hpa
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