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Subject: Re: [PATCH] rcu/tree: Force quiescent state on callback overload
To:     paulmck@kernel.org
Cc:     josh@joshtriplett.org, rostedt@goodmis.org,
        mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com,
        joel@joelfernandes.org, rcu@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <1592764647-2452-1-git-send-email-neeraju@codeaurora.org>
 <20200621195052.GF9247@paulmck-ThinkPad-P72>
From:   Neeraj Upadhyay <neeraju@codeaurora.org>
Message-ID: <94686c2e-b589-2598-e658-42f13cec1216@codeaurora.org>
Date:   Mon, 22 Jun 2020 01:30:31 +0530
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Hi Paul,

On 6/22/2020 1:20 AM, Paul E. McKenney wrote:
> On Mon, Jun 22, 2020 at 12:07:27AM +0530, Neeraj Upadhyay wrote:
>> On callback overload, we want to force quiescent state immediately,
>> for the first and second fqs. Enforce the same, by including
>> RCU_GP_FLAG_OVLD flag, in fqsstart check.
>>
>> Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
> 
> Good catch!
> 
> But what did you do to verify that this change does the right thing?
> 
> 						Thanx, Paul
> 

I haven't done a runtime verification of this code path; I posted this, 
based on review of this code.


Thanks
Neeraj

>> ---
>>   kernel/rcu/tree.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
>> index d0988a1..6226bfb 100644
>> --- a/kernel/rcu/tree.c
>> +++ b/kernel/rcu/tree.c
>> @@ -1865,7 +1865,7 @@ static void rcu_gp_fqs_loop(void)
>>   			break;
>>   		/* If time for quiescent-state forcing, do it. */
>>   		if (!time_after(rcu_state.jiffies_force_qs, jiffies) ||
>> -		    (gf & RCU_GP_FLAG_FQS)) {
>> +		    (gf & (RCU_GP_FLAG_FQS | RCU_GP_FLAG_OVLD))) {
>>   			trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
>>   					       TPS("fqsstart"));
>>   			rcu_gp_fqs(first_gp_fqs);
>> -- 
>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
>> a Linux Foundation Collaborative Project
>>

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