linux-kernel - Re: [PATCH] rcu: remove SPARSE_RCU

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Message-ID: <4D23C9B0.9060803@cn.fujitsu.com>
Date:	Wed, 05 Jan 2011 09:30:24 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	Arnd Bergmann <arnd@...db.de>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rcu: remove SPARSE_RCU_POINTER

On 01/05/2011 05:19 AM, Paul E. McKenney wrote:
> On Tue, Jan 04, 2011 at 11:36:02AM +0100, Arnd Bergmann wrote:
>> On Tuesday 04 January 2011 09:43:01 Lai Jiangshan wrote:
>>> As I known, __rcu annotations do not effect the result compiled kernel.
>>>
>>> They work only when we use spare("make C=1" or "make C=2"),
>>> So we don't need another new switch for it since we have one
>>> for debugging(use spare or not).
>>>
>>> signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
>>
>> The intention of this option was to avoid introducing an excessive
>> number of false positives when using sparse.
>>
>> We should only make that unconditional if we are reasonably convinced
>> that all the majority of warnings caused by it should actually
>> lead to changes in the code.
> 
> I agree with Arnd here -- the changes required are extensive in many
> cases, and a number of subsystems are making decent progress.
> 
> 							Thanx, Paul

I also agree. Most guys like to use direct read to the rcu pointer
on update side or direct read/write when initializing the rcu pointer.
This causes a lot of false positives.

Thanks,
Lai

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