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Subject: Re: [PATCH] rcu: Correct cpu offline trace in rcutree_dying_cpu
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: <1610365558-8330-1-git-send-email-neeraju@codeaurora.org>
 <20210112173116.GG2743@paulmck-ThinkPad-P72>
From:   Neeraj Upadhyay <neeraju@codeaurora.org>
Message-ID: <c1dd3362-7087-7141-4a4a-28d67db1924e@codeaurora.org>
Date:   Wed, 13 Jan 2021 10:41:20 +0530
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On 1/12/2021 11:01 PM, Paul E. McKenney wrote:
> On Mon, Jan 11, 2021 at 05:15:58PM +0530, Neeraj Upadhyay wrote:
>> Correctly trace whether the outgoing cpu blocks current gp in
>> rcutree_dying_cpu().
>>
>> Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
> 
> Good catch, queued, thank you!  Please see below for my usual
> wordsmithing, and please lat me know if I messed something up.
> 
> 							Thanx, Paul
> 

Thanks Paul, looks good!


Thanks
Neeraj

> ------------------------------------------------------------------------
> 
> commit ab6e7609e7590e1bb220ef6b0822a823dde46f6c
> Author: Neeraj Upadhyay <neeraju@codeaurora.org>
> Date:   Mon Jan 11 17:15:58 2021 +0530
> 
>      rcu: Fix CPU-offline trace in rcutree_dying_cpu
>      
>      The condition in the trace_rcu_grace_period() in rcutree_dying_cpu() is
>      backwards, so that it uses the string "cpuofl" when the offline CPU is
>      blocking the current grace period and "cpuofl-bgp" otherwise.  Given that
>      the "-bgp" stands for "blocking grace period", this is at best misleading.
>      This commit therefore switches these strings in order to correctly trace
>      whether the outgoing cpu blocks the current grace period.
>      
>      Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
>      Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index cc6b6fc..63c6dba 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2387,7 +2387,7 @@ int rcutree_dying_cpu(unsigned int cpu)
>   
>   	blkd = !!(rnp->qsmask & rdp->grpmask);
>   	trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
> -			       blkd ? TPS("cpuofl") : TPS("cpuofl-bgp"));
> +			       blkd ? TPS("cpuofl-bgp") : TPS("cpuofl"));
>   	return 0;
>   }
>   
> 

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