linux-kernel - Re: [PATCH] kernel/rcutree.c: deem to be lazy if there are no callbacks.

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Date:	Tue, 20 Aug 2013 12:30:12 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	dipankar@...ibm.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kernel/rcutree.c: deem to be lazy if there are no callbacks.

On 08/20/2013 12:10 PM, Paul E. McKenney wrote:
> On Tue, Aug 20, 2013 at 11:50:02AM +0800, Chen Gang wrote:
>> According to the comment above rcu_cpu_has_callbacks(): "If there are
>> no callbacks, all of them are deemed to be lazy".
>>
>> So when both 'hc' and 'al' are false, '*all_lazy' should be true, not
>> false.
> 
> If there are no callbacks, what must the value of "al" be at this
> point in the code?  Given this, what is the effect of your patch?
> 

Hmm... I find it by reading code, the 'C code' says that 'hc' and 'al'
has no relationships with each other, so for a reader they can assume
when 'hc' is false, 'al' can be either 'true' or 'false'.

> 							Thanx, Paul
> 
>> Signed-off-by: Chen Gang <gang.chen@...anux.com>
>> ---
>>  kernel/rcutree.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
>> index 5b53a89..9ee9565 100644
>> --- a/kernel/rcutree.c
>> +++ b/kernel/rcutree.c
>> @@ -2725,7 +2725,7 @@ static int rcu_cpu_has_callbacks(int cpu, bool *all_lazy)
>>  			hc = true;
>>  	}
>>  	if (all_lazy)
>> -		*all_lazy = al;
>> +		*all_lazy = !hc ? true : al;
>>  	return hc;
>>  }
>>
>> -- 
>> 1.7.7.6
>>
> 
> 
> 


-- 
Chen Gang
--
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