linux-kernel - Re: [PATCH] rcu/tree: Fix self wakeups for grace period kthread

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Message-ID: <579cd03a-17a7-5729-46b3-ffcc4afee0e5@codeaurora.org>
Date:   Tue, 12 Mar 2019 17:25:28 +0530
From:   Neeraj Upadhyay <neeraju@...eaurora.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     paulmck@...ux.vnet.ibm.com, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu/tree: Fix self wakeups for grace period kthread



On 3/12/19 7:20 AM, Steven Rostedt wrote:
> On Fri,  8 Mar 2019 15:16:18 +0530
> Neeraj Upadhyay <neeraju@...eaurora.org> wrote:
> 
>> Update the code to match the comment that self wakeup of
>> grace period kthread is allowed from interrupt handler, and
>> softirq handler, running in the grace period kthread's
>> context. Present code allows self wakeups from all
>> interrupt contexts - nmi, softirq and hardirq contexts.
> 
> That's not actually the issue. But it appears that we return if we
> simply have BH disabled, which I don't think we want, and we don't care
> about NMI as NMI should never call this code.
> 
> I think your patch is correct, but the change log is not.
> 
> -- Steve
> 

Hi Steve, sorry, I don't understand fully, why we want to not return in 
BH disabled case. From the commit logs and lkml discussion, there is a 
case where GP kthread is interrupted in the wait event path and 
rcu_gp_kthread_wake() is called in softirq handler (I am not sure about 
interrupt handler case; how rcu_gp_kthread_wake() is called from that path).

https://github.com/torvalds/linux/commit/1d1f898df6586c5ea9aeaf349f13089c6fa37903

Thanks
Neeraj
> 
>>
>> Signed-off-by: Neeraj Upadhyay <neeraju@...eaurora.org>
>> ---
>>   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 acd6ccf..57cac6d 100644
>> --- a/kernel/rcu/tree.c
>> +++ b/kernel/rcu/tree.c
>> @@ -1585,7 +1585,7 @@ static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
>>   static void rcu_gp_kthread_wake(void)
>>   {
>>   	if ((current == rcu_state.gp_kthread &&
>> -	     !in_interrupt() && !in_serving_softirq()) ||
>> +	     !in_irq() && !in_serving_softirq()) ||
>>   	    !READ_ONCE(rcu_state.gp_flags) ||
>>   	    !rcu_state.gp_kthread)
>>   		return;
> 

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