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

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Date:   Mon, 7 Aug 2017 19:31:27 +0530
From:   Neeraj Upadhyay <neeraju@...eaurora.org>
To:     paulmck@...ux.vnet.ibm.com
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 08/07/2017 06:10 PM, Paul E. McKenney wrote:
> 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

Hi Paul, found the issue while reading the code.

>
>> ---
>>   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
>>

-- 
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
member of the Code Aurora Forum, hosted by The Linux Foundation