Re: [PATCH] rcu: Fix up pending cbs check in rcu_prepare_for_idle

Neeraj Upadhyay
2017-08-07T14:01:35Z

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@codeaurora.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