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

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Message-ID: <20130820041054.GX29406@linux.vnet.ibm.com>
Date:	Mon, 19 Aug 2013 21:10:54 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Chen Gang <gang.chen@...anux.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 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?

							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
> 

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