linux-kernel - Re: [PATCH] rcu_do_batch: make ->qlen decrement irq safe

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Message-ID: <20060910221704.GH4690@in.ibm.com>
Date:	Mon, 11 Sep 2006 03:47:04 +0530
From:	Dipankar Sarma <dipankar@...ibm.com>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	"Paul E. McKenney" <paulmck@...ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu_do_batch: make ->qlen decrement irq safe

On Mon, Sep 11, 2006 at 01:32:43AM +0400, Oleg Nesterov wrote:
> rcu_do_batch() decrements rdp->qlen with irqs enabled. This is not good,
> it can also be modified by call_rcu() from interrupt.
> 
> Decrement ->qlen once with irqs disabled, after a main loop.
> 
> Signed-off-by: Oleg Nesterov <oleg@...sign.ru>
> 
> --- rc6-mm1/kernel/rcupdate.c~	2006-08-22 16:22:49.000000000 +0400
> +++ rc6-mm1/kernel/rcupdate.c	2006-09-11 01:24:17.000000000 +0400
> @@ -241,12 +241,16 @@ static void rcu_do_batch(struct rcu_data
>  		next = rdp->donelist = list->next;
>  		list->func(list);
>  		list = next;
> -		rdp->qlen--;
>  		if (++count >= rdp->blimit)
>  			break;
>  	}
> +
> +	local_irq_disable();
> +	rdp->qlen -= count;
> +	local_irq_enable();
>  	if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark)
>  		rdp->blimit = blimit;
> +
>  	if (!rdp->donelist)
>  		rdp->donetail = &rdp->donelist;
>  	else

Looks good to me. 

Thanks
Dipankar
-
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