linux-kernel - Re: [PATCH] rcu: Fix up pending cbs check in rcu_prepare_for

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Message-Id: <20170807124052.GU3730@linux.vnet.ibm.com>
Date:   Mon, 7 Aug 2017 05:40:52 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Neeraj Upadhyay <neeraju@...eaurora.org>
Cc:     josh@...htriplett.org, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu: Fix up pending cbs check in rcu_prepare_for_idle

On Mon, Aug 07, 2017 at 11:20:10AM +0530, Neeraj Upadhyay wrote:
> Pending cbs check in rcu_prepare_for_idle is inversed
> in the sense that, it should accelerate if there are
> pending cbs; but, the check does the opposite. So,
> fix it.
> 
> Fixes: 15fecf89e46a ("srcu: Abstract multi-tail callback list handling")
> Signed-off-by: Neeraj Upadhyay <neeraju@...eaurora.org>

Good catch!  Queued for review and testing.

Just out of curiosity, how did you find this one?

							Thanx, Paul

> ---
>  kernel/rcu/tree_plugin.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 908b309..b8f51df 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -1493,7 +1493,7 @@ static void rcu_prepare_for_idle(void)
>  	rdtp->last_accelerate = jiffies;
>  	for_each_rcu_flavor(rsp) {
>  		rdp = this_cpu_ptr(rsp->rda);
> -		if (rcu_segcblist_pend_cbs(&rdp->cblist))
> +		if (!rcu_segcblist_pend_cbs(&rdp->cblist))
>  			continue;
>  		rnp = rdp->mynode;
>  		raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
> -- 
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
> member of the Code Aurora Forum, hosted by The Linux Foundation
>