linux-kernel - Re: [PATCH] rcu: fix possible bug in include/linux/pagemap.h

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Message-ID: <4DB7957C.2070307@cn.fujitsu.com>
Date:	Wed, 27 Apr 2011 12:03:08 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Nick Piggin <npiggin@...nel.dk>
CC:	paulmck@...ux.vnet.ibm.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Américo Wang <xiyou.wangcong@...il.com>,
	stable@...nel.org, Greg Kroah-Hartman <gregkh@...e.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rcu: fix possible bug  in include/linux/pagemap.h

On 04/25/2011 09:48 PM, Paul E. McKenney wrote:
> On Mon, Apr 25, 2011 at 04:20:37PM +0800, Lai Jiangshan wrote:
>> I read the code and comments written by Nick Piggin(mainly from e286781d),
>> page_cache_get_speculative() is protected by rcu_read_lock(),
>> it may be preempted when preemptible RCU, so we must use get_page_unless_zero()
>> in this situation.
>>
>> In the days of e286781d, we only have CLASSIC_RCU and (old)PREEMPT_RCU,
>> so "defined(CONFIG_CLASSIC_RCU)" means non-preemptible RCU and the code is correct.
>>
>> In the days of b560d8ad, we only have TREE_RCU and TREE_PREEMPT_RCU,
>> so "defined(CONFIG_TREE_RCU)" means non-preemptible RCU and the code is correct.
>>
>> But in nowadays, we have TREE_RCU, TREE_PREEMPT_RCU, TINY_RCU and TINY_PREEMPT_RCU,
>> so the "defined(CONFIG_TREE_RCU)" for non-preemptible RCU is incorrect, and it may causes bugs.
>> we should use "!defined(CONFIG_PREEMPT_RCU)" for non-preemptible RCU code block.
>>
>> CC: Nick Piggin <npiggin@...nel.dk>
>> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
>> Reported-by: WANG Cong <amwang@...hat.com>
>> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> 
> Good catch!!!
> 
> Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 


Sorry, I forgot to CC it to LKML. Added it.


Hi, Nick Piggin,

Could you review it?

Thanks,
Lai
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